[hibernate-commits] Hibernate SVN: r15500 - in core/trunk/documentation/envers/src/main/docbook/en-US: images and 1 other directory.

Author: adamw Date: 2008-11-04 12:31:43 -0500 (Tue, 04 Nov 2008) New Revision: 15500 Removed: core/trunk/documentation/envers/src/main/docbook/en-US/content/architecture.xml core/trunk/documentation/envers/src/main/docbook/en-US/content/association_mapping.xml core/trunk/documentation/envers/src/main/docbook/en-US/content/basic_mapping.xml core/trunk/documentation/envers/src/main/docbook/en-US/content/batch.xml core/trunk/documentation/envers/src/main/docbook/en-US/content/best_practices.xml core/trunk/documentation/envers/src/main/docbook/en-US/content/collection_mapping.xml core/trunk/documentation/envers/src/main/docbook/en-US/content/component_mapping.xml core/trunk/documentation/envers/src/main/docbook/en-US/content/configuration.xml core/trunk/documentation/envers/src/main/docbook/en-US/content/events.xml core/trunk/documentation/envers/src/main/docbook/en-US/content/example_mappings.xml core/trunk/documentation/envers/src/main/docbook/en-US/content/example_parentchild.xml core/trunk/documentation/envers/src/main/docbook/en-US/content/example_weblog.xml core/trunk/documentation/envers/src/main/docbook/en-US/content/filters.xml core/trunk/documentation/envers/src/main/docbook/en-US/content/inheritance_mapping.xml core/trunk/documentation/envers/src/main/docbook/en-US/content/performance.xml core/trunk/documentation/envers/src/main/docbook/en-US/content/persistent_classes.xml core/trunk/documentation/envers/src/main/docbook/en-US/content/preface.xml core/trunk/documentation/envers/src/main/docbook/en-US/content/query_criteria.xml core/trunk/documentation/envers/src/main/docbook/en-US/content/query_hql.xml core/trunk/documentation/envers/src/main/docbook/en-US/content/query_sql.xml core/trunk/documentation/envers/src/main/docbook/en-US/content/session_api.xml core/trunk/documentation/envers/src/main/docbook/en-US/content/toolset_guide.xml core/trunk/documentation/envers/src/main/docbook/en-US/content/transactions.xml core/trunk/documentation/envers/src/main/docbook/en-US/content/tutorial.xml core/trunk/documentation/envers/src/main/docbook/en-US/content/xml.xml core/trunk/documentation/envers/src/main/docbook/en-US/images/AuthorWork.png core/trunk/documentation/envers/src/main/docbook/en-US/images/AuthorWork.zargo core/trunk/documentation/envers/src/main/docbook/en-US/images/CustomerOrderProduct.png core/trunk/documentation/envers/src/main/docbook/en-US/images/CustomerOrderProduct.zargo core/trunk/documentation/envers/src/main/docbook/en-US/images/EmployerEmployee.png core/trunk/documentation/envers/src/main/docbook/en-US/images/EmployerEmployee.zargo core/trunk/documentation/envers/src/main/docbook/en-US/images/full_cream.png core/trunk/documentation/envers/src/main/docbook/en-US/images/full_cream.svg core/trunk/documentation/envers/src/main/docbook/en-US/images/hibernate_logo_a.png core/trunk/documentation/envers/src/main/docbook/en-US/images/lite.png core/trunk/documentation/envers/src/main/docbook/en-US/images/lite.svg core/trunk/documentation/envers/src/main/docbook/en-US/images/overview.png core/trunk/documentation/envers/src/main/docbook/en-US/images/overview.svg Log: HHH-3556: Envers documentation partially migrated Deleted: core/trunk/documentation/envers/src/main/docbook/en-US/content/architecture.xml =================================================================== --- core/trunk/documentation/envers/src/main/docbook/en-US/content/architecture.xml 2008-11-04 17:31:01 UTC (rev 15499) +++ core/trunk/documentation/envers/src/main/docbook/en-US/content/architecture.xml 2008-11-04 17:31:43 UTC (rev 15500) @@ -1,382 +0,0 @@ -<?xml version='1.0' encoding="UTF-8"?> -<!-- - ~ Hibernate, Relational Persistence for Idiomatic Java - ~ - ~ Copyright (c) 2008, Red Hat Middleware LLC or third-party contributors as - ~ indicated by the @author tags or express copyright attribution - ~ statements applied by the authors. All third-party contributions are - ~ distributed under license by Red Hat Middleware LLC. - ~ - ~ This copyrighted material is made available to anyone wishing to use, modify, - ~ copy, or redistribute it subject to the terms and conditions of the GNU - ~ Lesser General Public License, as published by the Free Software Foundation. - ~ - ~ This program is distributed in the hope that it will be useful, - ~ but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY - ~ or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License - ~ for more details. - ~ - ~ You should have received a copy of the GNU Lesser General Public License - ~ along with this distribution; if not, write to: - ~ Free Software Foundation, Inc. - ~ 51 Franklin Street, Fifth Floor - ~ Boston, MA 02110-1301 USA - --> - -<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd"> - -<chapter id="architecture"> - - <title>Architecture</title> - - <sect1 id="architecture-overview" revision="1"> - <title>Overview</title> - - <para> - A (very) high-level view of the Hibernate architecture: - </para> - - <mediaobject> - <imageobject role="fo"> - <imagedata fileref="../images/overview.svg" format="SVG" align="center"/> - </imageobject> - <imageobject role="html"> - <imagedata fileref="../images/overview.png" format="PNG" align="center"/> - </imageobject> - </mediaobject> - - <para> - This diagram shows Hibernate using the database and configuration data to - provide persistence services (and persistent objects) to the application. - </para> - - <para> - We would like to show a more detailed view of the runtime architecture. - Unfortunately, Hibernate is flexible and supports several approaches. We will - show the two extremes. The "lite" architecture has the application - provide its own JDBC connections and manage its own transactions. This approach - uses a minimal subset of Hibernate's APIs: - </para> - - <mediaobject> - <imageobject role="fo"> - <imagedata fileref="../images/lite.svg" format="SVG" align="center"/> - </imageobject> - <imageobject role="html"> - <imagedata fileref="../images/lite.png" format="PNG" align="center"/> - </imageobject> - </mediaobject> - - <para> - The "full cream" architecture abstracts the application away from the - underlying JDBC/JTA APIs and lets Hibernate take care of the details. - </para> - - <mediaobject> - <imageobject role="fo"> - <imagedata fileref="../images/full_cream.svg" format="SVG" align="center"/> - </imageobject> - <imageobject role="html"> - <imagedata fileref="../images/full_cream.png" format="PNG" align="center"/> - </imageobject> - </mediaobject> - - <para> - Heres some definitions of the objects in the diagrams: - - <variablelist spacing="compact"> - <varlistentry> - <term>SessionFactory (<literal>org.hibernate.SessionFactory</literal>)</term> - <listitem> - <para> - A threadsafe (immutable) cache of compiled mappings for a single database. - A factory for <literal>Session</literal> and a client of - <literal>ConnectionProvider</literal>. Might hold an optional (second-level) - cache of data that is reusable between transactions, at a - process- or cluster-level. - </para> - </listitem> - </varlistentry> - <varlistentry> - <term>Session (<literal>org.hibernate.Session</literal>)</term> - <listitem> - <para> - A single-threaded, short-lived object representing a conversation between - the application and the persistent store. Wraps a JDBC connection. Factory - for <literal>Transaction</literal>. Holds a mandatory (first-level) cache - of persistent objects, used when navigating the object graph or looking up - objects by identifier. - </para> - </listitem> - </varlistentry> - <varlistentry> - <term>Persistent objects and collections</term> - <listitem> - <para> - Short-lived, single threaded objects containing persistent state and business - function. These might be ordinary JavaBeans/POJOs, the only special thing about - them is that they are currently associated with (exactly one) - <literal>Session</literal>. As soon as the <literal>Session</literal> is closed, - they will be detached and free to use in any application layer (e.g. directly - as data transfer objects to and from presentation). - </para> - </listitem> - </varlistentry> - <varlistentry> - <term>Transient and detached objects and collections</term> - <listitem> - <para> - Instances of persistent classes that are not currently associated with a - <literal>Session</literal>. They may have been instantiated by - the application and not (yet) persisted or they may have been instantiated by a - closed <literal>Session</literal>. - </para> - </listitem> - </varlistentry> - <varlistentry> - <term>Transaction (<literal>org.hibernate.Transaction</literal>)</term> - <listitem> - <para> - (Optional) A single-threaded, short-lived object used by the application to - specify atomic units of work. Abstracts application from underlying JDBC, - JTA or CORBA transaction. A <literal>Session</literal> might span several - <literal>Transaction</literal>s in some cases. However, transaction demarcation, - either using the underlying API or <literal>Transaction</literal>, is never - optional! - </para> - </listitem> - </varlistentry> - <varlistentry> - <term>ConnectionProvider (<literal>org.hibernate.connection.ConnectionProvider</literal>)</term> - <listitem> - <para> - (Optional) A factory for (and pool of) JDBC connections. Abstracts application from - underlying <literal>Datasource</literal> or <literal>DriverManager</literal>. - Not exposed to application, but can be extended/implemented by the developer. - </para> - </listitem> - </varlistentry> - <varlistentry> - <term>TransactionFactory (<literal>org.hibernate.TransactionFactory</literal>)</term> - <listitem> - <para> - (Optional) A factory for <literal>Transaction</literal> instances. Not exposed to the - application, but can be extended/implemented by the developer. - </para> - </listitem> - </varlistentry> - <varlistentry> - <term><emphasis>Extension Interfaces</emphasis></term> - <listitem> - <para> - Hibernate offers many optional extension interfaces you can implement to customize - the behavior of your persistence layer. See the API documentation for details. - </para> - </listitem> - </varlistentry> - </variablelist> - </para> - - <para> - Given a "lite" architecture, the application bypasses the - <literal>Transaction</literal>/<literal>TransactionFactory</literal> and/or - <literal>ConnectionProvider</literal> APIs to talk to JTA or JDBC directly. - </para> - </sect1> - - <sect1 id="architecture-states" revision="1"> - <title>Instance states</title> - <para> - An instance of a persistent classes may be in one of three different states, - which are defined with respect to a <emphasis>persistence context</emphasis>. - The Hibernate <literal>Session</literal> object is the persistence context: - </para> - - <variablelist spacing="compact"> - <varlistentry> - <term>transient</term> - <listitem> - <para> - The instance is not, and has never been associated with - any persistence context. It has no persistent identity - (primary key value). - </para> - </listitem> - </varlistentry> - <varlistentry> - <term>persistent</term> - <listitem> - <para> - The instance is currently associated with a persistence - context. It has a persistent identity (primary key value) - and, perhaps, a corresponding row in the database. For a - particular persistence context, Hibernate - <emphasis>guarantees</emphasis> that persistent identity - is equivalent to Java identity (in-memory location of the - object). - </para> - </listitem> - </varlistentry> - <varlistentry> - <term>detached</term> - <listitem> - <para> - The instance was once associated with a persistence - context, but that context was closed, or the instance - was serialized to another process. It has a persistent - identity and, perhaps, a corresponding row in the database. - For detached instances, Hibernate makes no guarantees - about the relationship between persistent identity and - Java identity. - </para> - </listitem> - </varlistentry> - </variablelist> - </sect1> - - <sect1 id="architecture-jmx" revision="1"> - <title>JMX Integration</title> - - <para> - JMX is the J2EE standard for management of Java components. Hibernate may be managed via - a JMX standard service. We provide an MBean implementation in the distribution, - <literal>org.hibernate.jmx.HibernateService</literal>. - </para> - - <para> - For an example how to deploy Hibernate as a JMX service on the JBoss Application Server, - please see the JBoss User Guide. On JBoss AS, you also get these benefits if you deploy - using JMX: - </para> - - <itemizedlist> - <listitem> - <para> - <emphasis>Session Management:</emphasis> The Hibernate <literal>Session</literal>'s life cycle - can be automatically bound to the scope of a JTA transaction. This means you no - longer have to manually open and close the <literal>Session</literal>, this - becomes the job of a JBoss EJB interceptor. You also don't have to worry about - transaction demarcation in your code anymore (unless you'd like to write a portable - persistence layer of course, use the optional Hibernate <literal>Transaction</literal> - API for this). You call the <literal>HibernateContext</literal> to access a - <literal>Session</literal>. - </para> - </listitem> - <listitem> - <para> - <emphasis>HAR deployment:</emphasis> Usually you deploy the Hibernate JMX service using a JBoss - service deployment descriptor (in an EAR and/or SAR file), it supports all the usual - configuration options of a Hibernate <literal>SessionFactory</literal>. However, you still - have to name all your mapping files in the deployment descriptor. If you decide to use - the optional HAR deployment, JBoss will automatically detect all mapping files in your - HAR file. - </para> - </listitem> - </itemizedlist> - - <para> - Consult the JBoss AS user guide for more information about these options. - </para> - - <para> - Another feature available as a JMX service are runtime Hibernate statistics. See - <xref linkend="configuration-optional-statistics"/>. - </para> - </sect1> - - <sect1 id="architecture-jca" revision="1"> - <title>JCA Support</title> - <para> - Hibernate may also be configured as a JCA connector. Please see the website for more - details. Please note that Hibernate JCA support is still considered experimental. - </para> - </sect1> - - <sect1 id="architecture-current-session" revision="2"> - <title>Contextual Sessions</title> - <para> - Most applications using Hibernate need some form of "contextual" sessions, where a given - session is in effect throughout the scope of a given context. However, across applications - the definition of what constitutes a context is typically different; and different contexts - define different scopes to the notion of current. Applications using Hibernate prior - to version 3.0 tended to utilize either home-grown <literal>ThreadLocal</literal>-based - contextual sessions, helper classes such as <literal>HibernateUtil</literal>, or utilized - third-party frameworks (such as Spring or Pico) which provided proxy/interception-based contextual sessions. - </para> - <para> - Starting with version 3.0.1, Hibernate added the <literal>SessionFactory.getCurrentSession()</literal> - method. Initially, this assumed usage of <literal>JTA</literal> transactions, where the - <literal>JTA</literal> transaction defined both the scope and context of a current session. - The Hibernate team maintains that, given the maturity of the numerous stand-alone - <literal>JTA TransactionManager</literal> implementations out there, most (if not all) - applications should be using <literal>JTA</literal> transaction management whether or not - they are deployed into a <literal>J2EE</literal> container. Based on that, the - <literal>JTA</literal>-based contextual sessions is all you should ever need to use. - </para> - <para> - However, as of version 3.1, the processing behind - <literal>SessionFactory.getCurrentSession()</literal> is now pluggable. To that - end, a new extension interface (<literal>org.hibernate.context.CurrentSessionContext</literal>) - and a new configuration parameter (<literal>hibernate.current_session_context_class</literal>) - have been added to allow pluggability of the scope and context of defining current sessions. - </para> - <para> - See the Javadocs for the <literal>org.hibernate.context.CurrentSessionContext</literal> - interface for a detailed discussion of its contract. It defines a single method, - <literal>currentSession()</literal>, by which the implementation is responsible for - tracking the current contextual session. Out-of-the-box, Hibernate comes with three - implementations of this interface. - </para> - - <itemizedlist> - <listitem> - <para> - <literal>org.hibernate.context.JTASessionContext</literal> - current sessions - are tracked and scoped by a <literal>JTA</literal> transaction. The processing - here is exactly the same as in the older JTA-only approach. See the Javadocs - for details. - </para> - </listitem> - <listitem> - <para> - <literal>org.hibernate.context.ThreadLocalSessionContext</literal> - current - sessions are tracked by thread of execution. Again, see the Javadocs for details. - </para> - </listitem> - <listitem> - <para> - <literal>org.hibernate.context.ManagedSessionContext</literal> - current - sessions are tracked by thread of execution. However, you are responsible to - bind and unbind a <literal>Session</literal> instance with static methods - on this class, it does never open, flush, or close a <literal>Session</literal>. - </para> - </listitem> - </itemizedlist> - - <para> - The first two implementations provide a "one session - one database transaction" programming - model, also known and used as <emphasis>session-per-request</emphasis>. The beginning - and end of a Hibernate session is defined by the duration of a database transaction. - If you use programmatic transaction demarcation in plain JSE without JTA, you are advised to - use the Hibernate <literal>Transaction</literal> API to hide the underlying transaction system - from your code. If you use JTA, use the JTA interfaces to demarcate transactions. If you - execute in an EJB container that supports CMT, transaction boundaries are defined declaratively - and you don't need any transaction or session demarcation operations in your code. - Refer to <xref linkend="transactions"/> for more information and code examples. - </para> - - <para> - The <literal>hibernate.current_session_context_class</literal> configuration parameter - defines which <literal>org.hibernate.context.CurrentSessionContext</literal> implementation - should be used. Note that for backwards compatibility, if this config param is not set - but a <literal>org.hibernate.transaction.TransactionManagerLookup</literal> is configured, - Hibernate will use the <literal>org.hibernate.context.JTASessionContext</literal>. - Typically, the value of this parameter would just name the implementation class to - use; for the three out-of-the-box implementations, however, there are three corresponding - short names, "jta", "thread", and "managed". - </para> - - </sect1> - -</chapter> - Deleted: core/trunk/documentation/envers/src/main/docbook/en-US/content/association_mapping.xml =================================================================== --- core/trunk/documentation/envers/src/main/docbook/en-US/content/association_mapping.xml 2008-11-04 17:31:01 UTC (rev 15499) +++ core/trunk/documentation/envers/src/main/docbook/en-US/content/association_mapping.xml 2008-11-04 17:31:43 UTC (rev 15500) @@ -1,650 +0,0 @@ -<?xml version='1.0' encoding="UTF-8"?> -<!-- - ~ Hibernate, Relational Persistence for Idiomatic Java - ~ - ~ Copyright (c) 2008, Red Hat Middleware LLC or third-party contributors as - ~ indicated by the @author tags or express copyright attribution - ~ statements applied by the authors. All third-party contributions are - ~ distributed under license by Red Hat Middleware LLC. - ~ - ~ This copyrighted material is made available to anyone wishing to use, modify, - ~ copy, or redistribute it subject to the terms and conditions of the GNU - ~ Lesser General Public License, as published by the Free Software Foundation. - ~ - ~ This program is distributed in the hope that it will be useful, - ~ but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY - ~ or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License - ~ for more details. - ~ - ~ You should have received a copy of the GNU Lesser General Public License - ~ along with this distribution; if not, write to: - ~ Free Software Foundation, Inc. - ~ 51 Franklin Street, Fifth Floor - ~ Boston, MA 02110-1301 USA - --> - -<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd"> - -<chapter id="associations"> - - <title>Association Mappings</title> - - <sect1 id="assoc-intro" revision="1"> - <title>Introduction</title> - - <para> - Association mappings are the often most difficult thing to get right. In - this section we'll go through the canonical cases one by one, starting - with unidirectional mappings, and then considering the bidirectional cases. - We'll use <literal>Person</literal> and <literal>Address</literal> in all - the examples. - </para> - - <para> - We'll classify associations by whether or not they map to an intervening - join table, and by multiplicity. - </para> - - <para> - Nullable foreign keys are not considered good practice in traditional data - modelling, so all our examples use not null foreign keys. This is not a - requirement of Hibernate, and the mappings will all work if you drop the - nullability constraints. - </para> - - </sect1> - - <sect1 id="assoc-unidirectional" revision="1"> - <title>Unidirectional associations</title> - - <sect2 id="assoc-unidirectional-m21"> - <title>many to one</title> - - <para> - A <emphasis>unidirectional many-to-one association</emphasis> is the most - common kind of unidirectional association. - </para> - - <programlisting><![CDATA[<class name="Person"> - <id name="id" column="personId"> - <generator class="native"/> - </id> - <many-to-one name="address" - column="addressId" - not-null="true"/> -</class> - -<class name="Address"> - <id name="id" column="addressId"> - <generator class="native"/> - </id> -</class>]]></programlisting> - <programlisting><![CDATA[ -create table Person ( personId bigint not null primary key, addressId bigint not null ) -create table Address ( addressId bigint not null primary key ) - ]]></programlisting> - - </sect2> - - <sect2 id="assoc-unidirectional-121"> - <title>one to one</title> - - <para> - A <emphasis>unidirectional one-to-one association on a foreign key</emphasis> - is almost identical. The only difference is the column unique constraint. - </para> - - <programlisting><![CDATA[<class name="Person"> - <id name="id" column="personId"> - <generator class="native"/> - </id> - <many-to-one name="address" - column="addressId" - unique="true" - not-null="true"/> -</class> - -<class name="Address"> - <id name="id" column="addressId"> - <generator class="native"/> - </id> -</class>]]></programlisting> - <programlisting><![CDATA[ -create table Person ( personId bigint not null primary key, addressId bigint not null unique ) -create table Address ( addressId bigint not null primary key ) - ]]></programlisting> - - <para> - A <emphasis>unidirectional one-to-one association on a primary key</emphasis> - usually uses a special id generator. (Notice that we've reversed the direction - of the association in this example.) - </para> - - <programlisting><![CDATA[<class name="Person"> - <id name="id" column="personId"> - <generator class="native"/> - </id> -</class> - -<class name="Address"> - <id name="id" column="personId"> - <generator class="foreign"> - <param name="property">person</param> - </generator> - </id> - <one-to-one name="person" constrained="true"/> -</class>]]></programlisting> - <programlisting><![CDATA[ -create table Person ( personId bigint not null primary key ) -create table Address ( personId bigint not null primary key ) - ]]></programlisting> - - </sect2> - - <sect2 id="assoc-unidirectional-12m"> - <title>one to many</title> - - <para> - A <emphasis>unidirectional one-to-many association on a foreign key</emphasis> - is a very unusual case, and is not really recommended. - </para> - - <programlisting><![CDATA[<class name="Person"> - <id name="id" column="personId"> - <generator class="native"/> - </id> - <set name="addresses"> - <key column="personId" - not-null="true"/> - <one-to-many class="Address"/> - </set> -</class> - -<class name="Address"> - <id name="id" column="addressId"> - <generator class="native"/> - </id> -</class>]]></programlisting> - <programlisting><![CDATA[ -create table Person ( personId bigint not null primary key ) -create table Address ( addressId bigint not null primary key, personId bigint not null ) - ]]></programlisting> - - <para> - We think it's better to use a join table for this kind of association. - </para> - - </sect2> - - </sect1> - - <sect1 id="assoc-unidirectional-join" revision="1"> - <title>Unidirectional associations with join tables</title> - - <sect2 id="assoc-unidirectional-join-12m"> - <title>one to many</title> - - <para> - A <emphasis>unidirectional one-to-many association on a join table</emphasis> - is much preferred. Notice that by specifying <literal>unique="true"</literal>, - we have changed the multiplicity from many-to-many to one-to-many. - </para> - - <programlisting><![CDATA[<class name="Person"> - <id name="id" column="personId"> - <generator class="native"/> - </id> - <set name="addresses" table="PersonAddress"> - <key column="personId"/> - <many-to-many column="addressId" - unique="true" - class="Address"/> - </set> -</class> - -<class name="Address"> - <id name="id" column="addressId"> - <generator class="native"/> - </id> -</class>]]></programlisting> - <programlisting><![CDATA[ -create table Person ( personId bigint not null primary key ) -create table PersonAddress ( personId not null, addressId bigint not null primary key ) -create table Address ( addressId bigint not null primary key ) - ]]></programlisting> - - </sect2> - - <sect2 id="assoc-unidirectional-join-m21"> - <title>many to one</title> - - <para> - A <emphasis>unidirectional many-to-one association on a join table</emphasis> - is quite common when the association is optional. - </para> - - <programlisting><![CDATA[<class name="Person"> - <id name="id" column="personId"> - <generator class="native"/> - </id> - <join table="PersonAddress" - optional="true"> - <key column="personId" unique="true"/> - <many-to-one name="address" - column="addressId" - not-null="true"/> - </join> -</class> - -<class name="Address"> - <id name="id" column="addressId"> - <generator class="native"/> - </id> -</class>]]></programlisting> - <programlisting><![CDATA[ -create table Person ( personId bigint not null primary key ) -create table PersonAddress ( personId bigint not null primary key, addressId bigint not null ) -create table Address ( addressId bigint not null primary key ) - ]]></programlisting> - - </sect2> - - <sect2 id="assoc-unidirectional-join-121"> - <title>one to one</title> - - <para> - A <emphasis>unidirectional one-to-one association on a join table</emphasis> - is extremely unusual, but possible. - </para> - - <programlisting><![CDATA[<class name="Person"> - <id name="id" column="personId"> - <generator class="native"/> - </id> - <join table="PersonAddress" - optional="true"> - <key column="personId" - unique="true"/> - <many-to-one name="address" - column="addressId" - not-null="true" - unique="true"/> - </join> -</class> - -<class name="Address"> - <id name="id" column="addressId"> - <generator class="native"/> - </id> -</class>]]></programlisting> - <programlisting><![CDATA[ -create table Person ( personId bigint not null primary key ) -create table PersonAddress ( personId bigint not null primary key, addressId bigint not null unique ) -create table Address ( addressId bigint not null primary key ) - ]]></programlisting> - - </sect2> - - <sect2 id="assoc-unidirectional-join-m2m"> - <title>many to many</title> - - <para> - Finally, we have a <emphasis>unidirectional many-to-many association</emphasis>. - </para> - - <programlisting><![CDATA[<class name="Person"> - <id name="id" column="personId"> - <generator class="native"/> - </id> - <set name="addresses" table="PersonAddress"> - <key column="personId"/> - <many-to-many column="addressId" - class="Address"/> - </set> -</class> - -<class name="Address"> - <id name="id" column="addressId"> - <generator class="native"/> - </id> -</class>]]></programlisting> - <programlisting><![CDATA[ -create table Person ( personId bigint not null primary key ) -create table PersonAddress ( personId bigint not null, addressId bigint not null, primary key (personId, addressId) ) -create table Address ( addressId bigint not null primary key ) - ]]></programlisting> - - </sect2> - - </sect1> - - <sect1 id="assoc-bidirectional" revision="1"> - <title>Bidirectional associations</title> - - <sect2 id="assoc-bidirectional-m21" revision="2"> - <title>one to many / many to one</title> - - <para> - A <emphasis>bidirectional many-to-one association</emphasis> is the - most common kind of association. (This is the standard parent/child - relationship.) - </para> - - <programlisting><![CDATA[<class name="Person"> - <id name="id" column="personId"> - <generator class="native"/> - </id> - <many-to-one name="address" - column="addressId" - not-null="true"/> -</class> - -<class name="Address"> - <id name="id" column="addressId"> - <generator class="native"/> - </id> - <set name="people" inverse="true"> - <key column="addressId"/> - <one-to-many class="Person"/> - </set> -</class>]]></programlisting> - - <programlisting><![CDATA[ -create table Person ( personId bigint not null primary key, addressId bigint not null ) -create table Address ( addressId bigint not null primary key ) - ]]></programlisting> - - <para> - If you use a <literal>List</literal> (or other indexed collection) you need - to set the <literal>key</literal> column of the foreign key to <literal>not null</literal>, - and let Hibernate manage the association from the collections side to maintain the index - of each element (making the other side virtually inverse by setting - <literal>update="false"</literal> and <literal>insert="false"</literal>): - </para> - - <programlisting><![CDATA[<class name="Person"> - <id name="id"/> - ... - <many-to-one name="address" - column="addressId" - not-null="true" - insert="false" - update="false"/> -</class> - -<class name="Address"> - <id name="id"/> - ... - <list name="people"> - <key column="addressId" not-null="true"/> - <list-index column="peopleIdx"/> - <one-to-many class="Person"/> - </list> -</class>]]></programlisting> - - <para> - It is important that you define <literal>not-null="true"</literal> on the - <literal>&lt;key&gt;</literal> element of the collection mapping if the - underlying foreign key column is <literal>NOT NULL</literal>. Don't only - declare <literal>not-null="true"</literal> on a possible nested - <literal>&lt;column&gt;</literal> element, but on the <literal>&lt;key&gt;</literal> - element. - </para> - - </sect2> - - <sect2 id="assoc-bidirectional-121"> - <title>one to one</title> - - <para> - A <emphasis>bidirectional one-to-one association on a foreign key</emphasis> - is quite common. - </para> - - <programlisting><![CDATA[<class name="Person"> - <id name="id" column="personId"> - <generator class="native"/> - </id> - <many-to-one name="address" - column="addressId" - unique="true" - not-null="true"/> -</class> - -<class name="Address"> - <id name="id" column="addressId"> - <generator class="native"/> - </id> - <one-to-one name="person" - property-ref="address"/> -</class>]]></programlisting> - <programlisting><![CDATA[ -create table Person ( personId bigint not null primary key, addressId bigint not null unique ) -create table Address ( addressId bigint not null primary key ) - ]]></programlisting> - - <para> - A <emphasis>bidirectional one-to-one association on a primary key</emphasis> - uses the special id generator. - </para> - - <programlisting><![CDATA[<class name="Person"> - <id name="id" column="personId"> - <generator class="native"/> - </id> - <one-to-one name="address"/> -</class> - -<class name="Address"> - <id name="id" column="personId"> - <generator class="foreign"> - <param name="property">person</param> - </generator> - </id> - <one-to-one name="person" - constrained="true"/> -</class>]]></programlisting> - <programlisting><![CDATA[ -create table Person ( personId bigint not null primary key ) -create table Address ( personId bigint not null primary key ) - ]]></programlisting> - - </sect2> - - </sect1> - - <sect1 id="assoc-bidirectional-join" revision="1"> - <title>Bidirectional associations with join tables</title> - - <sect2 id="assoc-bidirectional-join-12m"> - <title>one to many / many to one</title> - - <para> - A <emphasis>bidirectional one-to-many association on a join table</emphasis>. - Note that the <literal>inverse="true"</literal> can go on either end of the - association, on the collection, or on the join. - </para> - - <programlisting><![CDATA[<class name="Person"> - <id name="id" column="personId"> - <generator class="native"/> - </id> - <set name="addresses" - table="PersonAddress"> - <key column="personId"/> - <many-to-many column="addressId" - unique="true" - class="Address"/> - </set> -</class> - -<class name="Address"> - <id name="id" column="addressId"> - <generator class="native"/> - </id> - <join table="PersonAddress" - inverse="true" - optional="true"> - <key column="addressId"/> - <many-to-one name="person" - column="personId" - not-null="true"/> - </join> -</class>]]></programlisting> - <programlisting><![CDATA[ -create table Person ( personId bigint not null primary key ) -create table PersonAddress ( personId bigint not null, addressId bigint not null primary key ) -create table Address ( addressId bigint not null primary key ) - ]]></programlisting> - - </sect2> - - <sect2 id="assoc-bidirectional-join-121"> - <title>one to one</title> - - <para> - A <emphasis>bidirectional one-to-one association on a join table</emphasis> - is extremely unusual, but possible. - </para> - - <programlisting><![CDATA[<class name="Person"> - <id name="id" column="personId"> - <generator class="native"/> - </id> - <join table="PersonAddress" - optional="true"> - <key column="personId" - unique="true"/> - <many-to-one name="address" - column="addressId" - not-null="true" - unique="true"/> - </join> -</class> - -<class name="Address"> - <id name="id" column="addressId"> - <generator class="native"/> - </id> - <join table="PersonAddress" - optional="true" - inverse="true"> - <key column="addressId" - unique="true"/> - <many-to-one name="person" - column="personId" - not-null="true" - unique="true"/> - </join> -</class>]]></programlisting> - <programlisting><![CDATA[ -create table Person ( personId bigint not null primary key ) -create table PersonAddress ( personId bigint not null primary key, addressId bigint not null unique ) -create table Address ( addressId bigint not null primary key ) - ]]></programlisting> - - </sect2> - - <sect2 id="assoc-bidirectional-join-m2m" revision="1"> - <title>many to many</title> - - <para> - Finally, we have a <emphasis>bidirectional many-to-many association</emphasis>. - </para> - - <programlisting><![CDATA[<class name="Person"> - <id name="id" column="personId"> - <generator class="native"/> - </id> - <set name="addresses" table="PersonAddress"> - <key column="personId"/> - <many-to-many column="addressId" - class="Address"/> - </set> -</class> - -<class name="Address"> - <id name="id" column="addressId"> - <generator class="native"/> - </id> - <set name="people" inverse="true" table="PersonAddress"> - <key column="addressId"/> - <many-to-many column="personId" - class="Person"/> - </set> -</class>]]></programlisting> - - <programlisting><![CDATA[ -create table Person ( personId bigint not null primary key ) -create table PersonAddress ( personId bigint not null, addressId bigint not null, primary key (personId, addressId) ) -create table Address ( addressId bigint not null primary key ) - ]]></programlisting> - - </sect2> - - </sect1> - - <sect1 id="assoc-complex"> - <title>More complex association mappings</title> - - <para> - More complex association joins are <emphasis>extremely</emphasis> rare. - Hibernate makes it possible to handle more complex situations using - SQL fragments embedded in the mapping document. For example, if a table - with historical account information data defines - <literal>accountNumber</literal>, <literal>effectiveEndDate</literal> - and <literal>effectiveStartDate</literal>columns, mapped as follows: - </para> - - <programlisting><![CDATA[<properties name="currentAccountKey"> - <property name="accountNumber" type="string" not-null="true"/> - <property name="currentAccount" type="boolean"> - <formula>case when effectiveEndDate is null then 1 else 0 end</formula> - </property> -</properties> -<property name="effectiveEndDate" type="date"/> -<property name="effectiveStateDate" type="date" not-null="true"/>]]></programlisting> - - <para> - Then we can map an association to the <emphasis>current</emphasis> instance - (the one with null <literal>effectiveEndDate</literal>) using: - </para> - - <programlisting><![CDATA[<many-to-one name="currentAccountInfo" - property-ref="currentAccountKey" - class="AccountInfo"> - <column name="accountNumber"/> - <formula>'1'</formula> -</many-to-one>]]></programlisting> - - <para> - In a more complex example, imagine that the association between - <literal>Employee</literal> and <literal>Organization</literal> is maintained - in an <literal>Employment</literal> table full of historical employment data. - Then an association to the employee's <emphasis>most recent</emphasis> employer - (the one with the most recent <literal>startDate</literal>) might be mapped this way: - </para> - - <programlisting><![CDATA[<join> - <key column="employeeId"/> - <subselect> - select employeeId, orgId - from Employments - group by orgId - having startDate = max(startDate) - </subselect> - <many-to-one name="mostRecentEmployer" - class="Organization" - column="orgId"/> -</join>]]></programlisting> - - <para> - You can get quite creative with this functionality, but it is usually more practical - to handle these kinds of cases using HQL or a criteria query. - </para> - - </sect1> - - -</chapter> - Deleted: core/trunk/documentation/envers/src/main/docbook/en-US/content/basic_mapping.xml =================================================================== --- core/trunk/documentation/envers/src/main/docbook/en-US/content/basic_mapping.xml 2008-11-04 17:31:01 UTC (rev 15499) +++ core/trunk/documentation/envers/src/main/docbook/en-US/content/basic_mapping.xml 2008-11-04 17:31:43 UTC (rev 15500) @@ -1,3587 +0,0 @@ -<?xml version='1.0' encoding="UTF-8"?> -<!-- - ~ Hibernate, Relational Persistence for Idiomatic Java - ~ - ~ Copyright (c) 2008, Red Hat Middleware LLC or third-party contributors as - ~ indicated by the @author tags or express copyright attribution - ~ statements applied by the authors. All third-party contributions are - ~ distributed under license by Red Hat Middleware LLC. - ~ - ~ This copyrighted material is made available to anyone wishing to use, modify, - ~ copy, or redistribute it subject to the terms and conditions of the GNU - ~ Lesser General Public License, as published by the Free Software Foundation. - ~ - ~ This program is distributed in the hope that it will be useful, - ~ but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY - ~ or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License - ~ for more details. - ~ - ~ You should have received a copy of the GNU Lesser General Public License - ~ along with this distribution; if not, write to: - ~ Free Software Foundation, Inc. - ~ 51 Franklin Street, Fifth Floor - ~ Boston, MA 02110-1301 USA - --> - -<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd"> - -<chapter id="mapping"> - <title>Basic O/R Mapping</title> - - <sect1 id="mapping-declaration" revision="2"> - <title>Mapping declaration</title> - - <para> - Object/relational mappings are usually defined in an XML document. The mapping - document is designed to be readable and hand-editable. The mapping language is - Java-centric, meaning that mappings are constructed around persistent class - declarations, not table declarations. - </para> - - <para> - Note that, even though many Hibernate users choose to write the XML by hand, - a number of tools exist to generate the mapping document, including XDoclet, - Middlegen and AndroMDA. - </para> - - <para> - Lets kick off with an example mapping: - </para> - - <programlisting id="mapping-declaration-ex1" revision="1"><![CDATA[<?xml version="1.0"?> -<!DOCTYPE hibernate-mapping PUBLIC - "-//Hibernate/Hibernate Mapping DTD 3.0//EN" - "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> - -<hibernate-mapping package="eg"> - - <class name="Cat" - table="cats" - discriminator-value="C"> - - <id name="id"> - <generator class="native"/> - </id> - - <discriminator column="subclass" - type="character"/> - - <property name="weight"/> - - <property name="birthdate" - type="date" - not-null="true" - update="false"/> - - <property name="color" - type="eg.types.ColorUserType" - not-null="true" - update="false"/> - - <property name="sex" - not-null="true" - update="false"/> - - <property name="litterId" - column="litterId" - update="false"/> - - <many-to-one name="mother" - column="mother_id" - update="false"/> - - <set name="kittens" - inverse="true" - order-by="litter_id"> - <key column="mother_id"/> - <one-to-many class="Cat"/> - </set> - - <subclass name="DomesticCat" - discriminator-value="D"> - - <property name="name" - type="string"/> - - </subclass> - - </class> - - <class name="Dog"> - <!-- mapping for Dog could go here --> - </class> - -</hibernate-mapping>]]></programlisting> - - <para> - We will now discuss the content of the mapping document. We will only describe the - document elements and attributes that are used by Hibernate at runtime. The mapping - document also contains some extra optional attributes and elements that affect the - database schemas exported by the schema export tool. (For example the <literal> - not-null</literal> attribute.) - </para> - - - - <sect2 id="mapping-declaration-doctype" revision="3"> - <title>Doctype</title> - - <para> - All XML mappings should declare the doctype shown. The actual DTD may be found - at the URL above, in the directory <literal>hibernate-x.x.x/src/org/hibernate - </literal> or in <literal>hibernate3.jar</literal>. Hibernate will always look for - the DTD in its classpath first. If you experience lookups of the DTD using an - Internet connection, check your DTD declaration against the contents of your - claspath. - </para> - - <sect3 id="mapping-declaration-entity-resolution"> - <title>EntityResolver</title> - <para> - As mentioned previously, Hibernate will first attempt to resolve DTDs in its classpath. The - manner in which it does this is by registering a custom <literal>org.xml.sax.EntityResolver</literal> - implementation with the SAXReader it uses to read in the xml files. This custom - <literal>EntityResolver</literal> recognizes two different systemId namespaces. - </para> - <itemizedlist> - <listitem> - <para> - a <literal>hibernate namespace</literal> is recognized whenever the - resolver encounteres a systemId starting with - <literal>http://hibernate.sourceforge.net/</literal>; the resolver - attempts to resolve these entities via the classlaoder which loaded - the Hibernate classes. - </para> - </listitem> - <listitem> - <para> - a <literal>user namespace</literal> is recognized whenever the - resolver encounteres a systemId using a <literal>classpath://</literal> - URL protocol; the resolver will attempt to resolve these entities - via (1) the current thread context classloader and (2) the - classloader which loaded the Hibernate classes. - </para> - </listitem> - </itemizedlist> - <para> - An example of utilizing user namespacing: - </para> - <programlisting><![CDATA[<?xml version="1.0"?> -<!DOCTYPE hibernate-mapping PUBLIC - "-//Hibernate/Hibernate Mapping DTD 3.0//EN" - "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd" [ - <!ENTITY types SYSTEM "classpath://your/domain/types.xml"> -]> - -<hibernate-mapping package="your.domain"> - <class name="MyEntity"> - <id name="id" type="my-custom-id-type"> - ... - </id> - <class> - &types; -</hibernate-mapping>]]></programlisting> - <para> - Where <literal>types.xml</literal> is a resource in the <literal>your.domain</literal> - package and contains a custom <link linkend="mapping-types-custom">typedef</link>. - </para> - </sect3> - </sect2> - - <sect2 id="mapping-declaration-mapping" revision="3"> - <title>hibernate-mapping</title> - - <para> - This element has several optional attributes. The <literal>schema</literal> and - <literal>catalog</literal> attributes specify that tables referred to in this mapping - belong to the named schema and/or catalog. If specified, tablenames will be qualified - by the given schema and catalog names. If missing, tablenames will be unqualified. - The <literal>default-cascade</literal> attribute specifies what cascade style - should be assumed for properties and collections which do not specify a - <literal>cascade</literal> attribute. The <literal>auto-import</literal> attribute lets us - use unqualified class names in the query language, by default. - </para> - - <programlistingco> - <areaspec> - <area id="hm1" coords="2 55"/> - <area id="hm2" coords="3 55"/> - <area id="hm3" coords="4 55"/> - <area id="hm4" coords="5 55"/> - <area id="hm5" coords="6 55"/> - <area id="hm6" coords="7 55"/> - <area id="hm7" coords="8 55"/> - </areaspec> - <programlisting><![CDATA[<hibernate-mapping - schema="schemaName" - catalog="catalogName" - default-cascade="cascade_style" - default-access="field|property|ClassName" - default-lazy="true|false" - auto-import="true|false" - package="package.name" - />]]></programlisting> - <calloutlist> - <callout arearefs="hm1"> - <para> - <literal>schema</literal> (optional): The name of a database schema. - </para> - </callout> - <callout arearefs="hm2"> - <para> - <literal>catalog</literal> (optional): The name of a database catalog. - </para> - </callout> - <callout arearefs="hm3"> - <para> - <literal>default-cascade</literal> (optional - defaults to <literal>none</literal>): - A default cascade style. - </para> - </callout> - <callout arearefs="hm4"> - <para> - <literal>default-access</literal> (optional - defaults to <literal>property</literal>): - The strategy Hibernate should use for accessing all properties. Can be a custom - implementation of <literal>PropertyAccessor</literal>. - </para> - </callout> - <callout arearefs="hm5"> - <para> - <literal>default-lazy</literal> (optional - defaults to <literal>true</literal>): - The default value for unspecifed <literal>lazy</literal> attributes of class and - collection mappings. - </para> - </callout> - <callout arearefs="hm6"> - <para> - <literal>auto-import</literal> (optional - defaults to <literal>true</literal>): - Specifies whether we can use unqualified class names (of classes in this mapping) - in the query language. - </para> - </callout> - <callout arearefs="hm7"> - <para> - <literal>package</literal> (optional): Specifies a package prefix to assume for - unqualified class names in the mapping document. - </para> - </callout> - </calloutlist> - </programlistingco> - - <para> - If you have two persistent classes with the same (unqualified) name, you should set - <literal>auto-import="false"</literal>. Hibernate will throw an exception if you attempt - to assign two classes to the same "imported" name. - </para> - - <para> - Note that the <literal>hibernate-mapping</literal> element allows you to nest - several persistent <literal>&lt;class&gt;</literal> mappings, as shown above. - It is however good practice (and expected by some tools) to map only a single - persistent class (or a single class hierarchy) in one mapping file and name - it after the persistent superclass, e.g. <literal>Cat.hbm.xml</literal>, - <literal>Dog.hbm.xml</literal>, or if using inheritance, - <literal>Animal.hbm.xml</literal>. - </para> - - </sect2> - - <sect2 id="mapping-declaration-class" revision="3"> - <title>class</title> - - <para> - You may declare a persistent class using the <literal>class</literal> element: - </para> - - <programlistingco> - <areaspec> - <area id="class1" coords="2 55"/> - <area id="class2" coords="3 55" /> - <area id="class3" coords="4 55"/> - <area id="class4" coords="5 55" /> - <area id="class5" coords="6 55"/> - <area id="class6" coords="7 55" /> - <area id="class7" coords="8 55"/> - <area id="class8" coords="9 55" /> - <area id="class9" coords="10 55" /> - <area id="class10" coords="11 55"/> - <area id="class11" coords="12 55"/> - <area id="class12" coords="13 55"/> - <area id="class13" coords="14 55"/> - <area id="class14" coords="15 55"/> - <area id="class15" coords="16 55"/> - <area id="class16" coords="17 55"/> - <area id="class17" coords="18 55"/> - <area id="class18" coords="19 55"/> - <area id="class19" coords="20 55"/> - <area id="class20" coords="21 55"/> - <area id="class21" coords="22 55"/> - </areaspec> - <programlisting><![CDATA[<class - name="ClassName" - table="tableName" - discriminator-value="discriminator_value" - mutable="true|false" - schema="owner" - catalog="catalog" - proxy="ProxyInterface" - dynamic-update="true|false" - dynamic-insert="true|false" - select-before-update="true|false" - polymorphism="implicit|explicit" - where="arbitrary sql where condition" - persister="PersisterClass" - batch-size="N" - optimistic-lock="none|version|dirty|all" - lazy="true|false" - entity-name="EntityName" - check="arbitrary sql check condition" - rowid="rowid" - subselect="SQL expression" - abstract="true|false" - node="element-name" -/>]]></programlisting> - <calloutlist> - <callout arearefs="class1"> - <para> - <literal>name</literal> (optional): The fully qualified Java class name of the - persistent class (or interface). If this attribute is missing, it is assumed - that the mapping is for a non-POJO entity. - </para> - </callout> - <callout arearefs="class2"> - <para> - <literal>table</literal> (optional - defaults to the unqualified class name): The - name of its database table. - </para> - </callout> - <callout arearefs="class3"> - <para> - <literal>discriminator-value</literal> (optional - defaults to the class name): A value - that distiguishes individual subclasses, used for polymorphic behaviour. Acceptable - values include <literal>null</literal> and <literal>not null</literal>. - </para> - </callout> - <callout arearefs="class4"> - <para> - <literal>mutable</literal> (optional, defaults to <literal>true</literal>): Specifies - that instances of the class are (not) mutable. - </para> - </callout> - <callout arearefs="class5"> - <para> - <literal>schema</literal> (optional): Override the schema name specified by - the root <literal>&lt;hibernate-mapping&gt;</literal> element. - </para> - </callout> - <callout arearefs="class6"> - <para> - <literal>catalog</literal> (optional): Override the catalog name specified by - the root <literal>&lt;hibernate-mapping&gt;</literal> element. - </para> - </callout> - <callout arearefs="class7"> - <para> - <literal>proxy</literal> (optional): Specifies an interface to use for lazy - initializing proxies. You may specify the name of the class itself. - </para> - </callout> - <callout arearefs="class8"> - <para> - <literal>dynamic-update</literal> (optional, defaults to <literal>false</literal>): - Specifies that <literal>UPDATE</literal> SQL should be generated at runtime and - contain only those columns whose values have changed. - </para> - </callout> - <callout arearefs="class9"> - <para> - <literal>dynamic-insert</literal> (optional, defaults to <literal>false</literal>): - Specifies that <literal>INSERT</literal> SQL should be generated at runtime and - contain only the columns whose values are not null. - </para> - </callout> - <callout arearefs="class10"> - <para> - <literal>select-before-update</literal> (optional, defaults to <literal>false</literal>): - Specifies that Hibernate should <emphasis>never</emphasis> perform an SQL <literal>UPDATE</literal> - unless it is certain that an object is actually modified. In certain cases (actually, only - when a transient object has been associated with a new session using <literal>update()</literal>), - this means that Hibernate will perform an extra SQL <literal>SELECT</literal> to determine - if an <literal>UPDATE</literal> is actually required. - </para> - </callout> - <callout arearefs="class11"> - <para> - <literal>polymorphism</literal> (optional, defaults to <literal>implicit</literal>): - Determines whether implicit or explicit query polymorphism is used. - </para> - </callout> - <callout arearefs="class12"> - <para> - <literal>where</literal> (optional) specify an arbitrary SQL <literal>WHERE</literal> - condition to be used when retrieving objects of this class - </para> - </callout> - <callout arearefs="class13"> - <para> - <literal>persister</literal> (optional): Specifies a custom <literal>ClassPersister</literal>. - </para> - </callout> - <callout arearefs="class14"> - <para> - <literal>batch-size</literal> (optional, defaults to <literal>1</literal>) specify a "batch size" - for fetching instances of this class by identifier. - </para> - </callout> - <callout arearefs="class15"> - <para> - <literal>optimistic-lock</literal> (optional, defaults to <literal>version</literal>): - Determines the optimistic locking strategy. - </para> - </callout> - <callout arearefs="class16"> - <para> - <literal>lazy</literal> (optional): Lazy fetching may be completely disabled by setting - <literal>lazy="false"</literal>. - </para> - </callout> - <callout arearefs="class17"> - <para> - <literal>entity-name</literal> (optional, defaults to the class name): Hibernate3 - allows a class to be mapped multiple times (to different tables, potentially), - and allows entity mappings that are represented by Maps or XML at the Java level. - In these cases, you should provide an explicit arbitrary name for the entity. See - <xref linkend="persistent-classes-dynamicmodels"/> and <xref linkend="xml"/> - for more information. - </para> - </callout> - <callout arearefs="class18"> - <para> - <literal>check</literal> (optional): A SQL expression used to generate a multi-row - <emphasis>check</emphasis> constraint for automatic schema generation. - </para> - </callout> - <callout arearefs="class19"> - <para> - <literal>rowid</literal> (optional): Hibernate can use so called ROWIDs on databases - which support. E.g. on Oracle, Hibernate can use the <literal>rowid</literal> extra - column for fast updates if you set this option to <literal>rowid</literal>. A ROWID - is an implementation detail and represents the physical location of a stored tuple. - </para> - </callout> - <callout arearefs="class20"> - <para> - <literal>subselect</literal> (optional): Maps an immutable and read-only entity - to a database subselect. Useful if you want to have a view instead of a base table, - but don't. See below for more information. - </para> - </callout> - <callout arearefs="class21"> - <para> - <literal>abstract</literal> (optional): Used to mark abstract superclasses in - <literal>&lt;union-subclass&gt;</literal> hierarchies. - </para> - </callout> - </calloutlist> - </programlistingco> - - <para> - It is perfectly acceptable for the named persistent class to be an interface. You would then - declare implementing classes of that interface using the <literal>&lt;subclass&gt;</literal> - element. You may persist any <emphasis>static</emphasis> inner class. You should specify the - class name using the standard form ie. <literal>eg.Foo$Bar</literal>. - </para> - - <para> - Immutable classes, <literal>mutable="false"</literal>, may not be updated or deleted by the - application. This allows Hibernate to make some minor performance optimizations. - </para> - - <para> - The optional <literal>proxy</literal> attribute enables lazy initialization of persistent - instances of the class. Hibernate will initially return CGLIB proxies which implement - the named interface. The actual persistent object will be loaded when a method of the - proxy is invoked. See "Initializing collections and proxies" below. - </para> - - <para><emphasis>Implicit</emphasis> polymorphism means that instances of the class will be returned - by a query that names any superclass or implemented interface or the class and that instances - of any subclass of the class will be returned by a query that names the class itself. - <emphasis>Explicit</emphasis> polymorphism means that class instances will be returned only - by queries that explicitly name that class and that queries that name the class will return - only instances of subclasses mapped inside this <literal>&lt;class&gt;</literal> declaration - as a <literal>&lt;subclass&gt;</literal> or <literal>&lt;joined-subclass&gt;</literal>. For - most purposes the default, <literal>polymorphism="implicit"</literal>, is appropriate. - Explicit polymorphism is useful when two different classes are mapped to the same table - (this allows a "lightweight" class that contains a subset of the table columns). - </para> - - <para> - The <literal>persister</literal> attribute lets you customize the persistence strategy used for - the class. You may, for example, specify your own subclass of - <literal>org.hibernate.persister.EntityPersister</literal> or you might even provide a - completely new implementation of the interface - <literal>org.hibernate.persister.ClassPersister</literal> that implements persistence via, - for example, stored procedure calls, serialization to flat files or LDAP. See - <literal>org.hibernate.test.CustomPersister</literal> for a simple example (of "persistence" - to a <literal>Hashtable</literal>). - </para> - - <para> - Note that the <literal>dynamic-update</literal> and <literal>dynamic-insert</literal> - settings are not inherited by subclasses and so may also be specified on the - <literal>&lt;subclass&gt;</literal> or <literal>&lt;joined-subclass&gt;</literal> elements. - These settings may increase performance in some cases, but might actually decrease - performance in others. Use judiciously. - </para> - - <para> - Use of <literal>select-before-update</literal> will usually decrease performance. It is very - useful to prevent a database update trigger being called unnecessarily if you reattach a - graph of detached instances to a <literal>Session</literal>. - </para> - - <para> - If you enable <literal>dynamic-update</literal>, you will have a choice of optimistic - locking strategies: - </para> - <itemizedlist> - <listitem> - <para> - <literal>version</literal> check the version/timestamp columns - </para> - </listitem> - <listitem> - <para> - <literal>all</literal> check all columns - </para> - </listitem> - <listitem> - <para> - <literal>dirty</literal> check the changed columns, allowing some concurrent updates - </para> - </listitem> - <listitem> - <para> - <literal>none</literal> do not use optimistic locking - </para> - </listitem> - </itemizedlist> - <para> - We <emphasis>very</emphasis> strongly recommend that you use version/timestamp - columns for optimistic locking with Hibernate. This is the optimal strategy with - respect to performance and is the only strategy that correctly handles modifications - made to detached instances (ie. when <literal>Session.merge()</literal> is used). - </para> - - <para> - There is no difference between a view and a base table for a Hibernate mapping, as - expected this is transparent at the database level (note that some DBMS don't support - views properly, especially with updates). Sometimes you want to use a view, but can't - create one in the database (ie. with a legacy schema). In this case, you can map an - immutable and read-only entity to a given SQL subselect expression: - </para> - - <programlisting><![CDATA[<class name="Summary"> - <subselect> - select item.name, max(bid.amount), count(*) - from item - join bid on bid.item_id = item.id - group by item.name - </subselect> - <synchronize table="item"/> - <synchronize table="bid"/> - <id name="name"/> - ... -</class>]]></programlisting> - - <para> - Declare the tables to synchronize this entity with, ensuring that auto-flush happens - correctly, and that queries against the derived entity do not return stale data. - The <literal>&lt;subselect&gt;</literal> is available as both as an attribute and - a nested mapping element. - </para> - - </sect2> - - <sect2 id="mapping-declaration-id" revision="4"> - <title>id</title> - - <para> - Mapped classes <emphasis>must</emphasis> declare the primary key column of the database - table. Most classes will also have a JavaBeans-style property holding the unique identifier - of an instance. The <literal>&lt;id&gt;</literal> element defines the mapping from that - property to the primary key column. - </para> - - <programlistingco> - <areaspec> - <area id="id1" coords="2 70"/> - <area id="id2" coords="3 70" /> - <area id="id3" coords="4 70"/> - <area id="id4" coords="5 70" /> - <area id="id5" coords="6 70" /> - </areaspec> - <programlisting><![CDATA[<id - name="propertyName" - type="typename" - column="column_name" - unsaved-value="null|any|none|undefined|id_value" - access="field|property|ClassName"> - node=&quot;element-name|@attribute-name|element/(a)attribute|.&quot; - - <generator class="generatorClass"/> -</id>]]></programlisting> - <calloutlist> - <callout arearefs="id1"> - <para> - <literal>name</literal> (optional): The name of the identifier property. - </para> - </callout> - <callout arearefs="id2"> - <para> - <literal>type</literal> (optional): A name that indicates the Hibernate type. - </para> - </callout> - <callout arearefs="id3"> - <para> - <literal>column</literal> (optional - defaults to the property name): The - name of the primary key column. - </para> - </callout> - <callout arearefs="id4"> - <para> - <literal>unsaved-value</literal> (optional - defaults to a "sensible" value): - An identifier property value that indicates that an instance is newly instantiated - (unsaved), distinguishing it from detached instances that were saved or loaded - in a previous session. - </para> - </callout> - <callout arearefs="id5"> - <para> - <literal>access</literal> (optional - defaults to <literal>property</literal>): The - strategy Hibernate should use for accessing the property value. - </para> - </callout> - </calloutlist> - </programlistingco> - - <para> - If the <literal>name</literal> attribute is missing, it is assumed that the class has no - identifier property. - </para> - - <para> - The <literal>unsaved-value</literal> attribute is almost never needed in Hibernate3. - </para> - - <para> - There is an alternative <literal>&lt;composite-id&gt;</literal> declaration to allow access to - legacy data with composite keys. We strongly discourage its use for anything else. - </para> - - <sect3 id="mapping-declaration-id-generator" revision="2"> - <title>Generator</title> - - <para> - The optional <literal>&lt;generator&gt;</literal> child element names a Java class used - to generate unique identifiers for instances of the persistent class. If any parameters - are required to configure or initialize the generator instance, they are passed using the - <literal>&lt;param&gt;</literal> element. - </para> - - <programlisting><![CDATA[<id name="id" type="long" column="cat_id"> - <generator class="org.hibernate.id.TableHiLoGenerator"> - <param name="table">uid_table</param> - <param name="column">next_hi_value_column</param> - </generator> -</id>]]></programlisting> - - <para> - All generators implement the interface <literal>org.hibernate.id.IdentifierGenerator</literal>. - This is a very simple interface; some applications may choose to provide their own specialized - implementations. However, Hibernate provides a range of built-in implementations. There are shortcut - names for the built-in generators: - - <variablelist> - <varlistentry> - <term><literal>increment</literal></term> - <listitem> - <para> - generates identifiers of type <literal>long</literal>, <literal>short</literal> or - <literal>int</literal> that are unique only when no other process is inserting data - into the same table. - <emphasis>Do not use in a cluster.</emphasis> - </para> - </listitem> - </varlistentry> - <varlistentry> - <term><literal>identity</literal></term> - <listitem> - <para> - supports identity columns in DB2, MySQL, MS SQL Server, Sybase and - HypersonicSQL. The returned identifier is of type <literal>long</literal>, - <literal>short</literal> or <literal>int</literal>. - </para> - </listitem> - </varlistentry> - <varlistentry> - <term><literal>sequence</literal></term> - <listitem> - <para> - uses a sequence in DB2, PostgreSQL, Oracle, SAP DB, McKoi or a generator - in Interbase. The returned identifier is of type <literal>long</literal>, - <literal>short</literal> or <literal>int</literal> - </para> - </listitem> - </varlistentry> - <varlistentry> - <term><literal>hilo</literal></term> - <listitem> - <para id="mapping-declaration-id-hilodescription" revision="1"> - uses a hi/lo algorithm to efficiently generate identifiers of - type <literal>long</literal>, <literal>short</literal> or <literal>int</literal>, - given a table and column (by default <literal>hibernate_unique_key</literal> and - <literal>next_hi</literal> respectively) as a source of hi values. The hi/lo - algorithm generates identifiers that are unique only for a particular database. - </para> - </listitem> - </varlistentry> - <varlistentry> - <term><literal>seqhilo</literal></term> - <listitem> - <para> - uses a hi/lo algorithm to efficiently generate identifiers of type - <literal>long</literal>, <literal>short</literal> or <literal>int</literal>, - given a named database sequence. - </para> - </listitem> - </varlistentry> - <varlistentry> - <term><literal>uuid</literal></term> - <listitem> - <para> - uses a 128-bit UUID algorithm to generate identifiers of type string, - unique within a network (the IP address is used). The UUID is encoded - as a string of hexadecimal digits of length 32. - </para> - </listitem> - </varlistentry> - <varlistentry> - <term><literal>guid</literal></term> - <listitem> - <para> - uses a database-generated GUID string on MS SQL Server and MySQL. - </para> - </listitem> - </varlistentry> - <varlistentry> - <term><literal>native</literal></term> - <listitem> - <para> - picks <literal>identity</literal>, <literal>sequence</literal> or - <literal>hilo</literal> depending upon the capabilities of the - underlying database. - </para> - </listitem> - </varlistentry> - <varlistentry> - <term><literal>assigned</literal></term> - <listitem> - <para> - lets the application to assign an identifier to the object before - <literal>save()</literal> is called. This is the default strategy - if no <literal>&lt;generator&gt;</literal> element is specified. - </para> - </listitem> - </varlistentry> - <varlistentry> - <term><literal>select</literal></term> - <listitem> - <para> - retrieves a primary key assigned by a database trigger by selecting - the row by some unique key and retrieving the primary key value. - </para> - </listitem> - </varlistentry> - <varlistentry> - <term><literal>foreign</literal></term> - <listitem> - <para> - uses the identifier of another associated object. Usually used in conjunction - with a <literal>&lt;one-to-one&gt;</literal> primary key association. - </para> - </listitem> - </varlistentry> - <varlistentry> - <term><literal>sequence-identity</literal></term> - <listitem> - <para> - a specialized sequence generation strategy which utilizes a - database sequence for the actual value generation, but combines - this with JDBC3 getGeneratedKeys to actually return the generated - identifier value as part of the insert statement execution. This - strategy is only known to be supported on Oracle 10g drivers - targetted for JDK 1.4. Note comments on these insert statements - are disabled due to a bug in the Oracle drivers. - </para> - </listitem> - </varlistentry> - </variablelist> - - </para> - </sect3> - - <sect3 id="mapping-declaration-id-hilo" revision="1"> - <title>Hi/lo algorithm</title> - <para> - The <literal>hilo</literal> and <literal>seqhilo</literal> generators provide two alternate - implementations of the hi/lo algorithm, a favorite approach to identifier generation. The - first implementation requires a "special" database table to hold the next available "hi" value. - The second uses an Oracle-style sequence (where supported). - </para> - - <programlisting><![CDATA[<id name="id" type="long" column="cat_id"> - <generator class="hilo"> - <param name="table">hi_value</param> - <param name="column">next_value</param> - <param name="max_lo">100</param> - </generator> -</id>]]></programlisting> - - <programlisting><![CDATA[<id name="id" type="long" column="cat_id"> - <generator class="seqhilo"> - <param name="sequence">hi_value</param> - <param name="max_lo">100</param> - </generator> -</id>]]></programlisting> - - <para> - Unfortunately, you can't use <literal>hilo</literal> when supplying your own - <literal>Connection</literal> to Hibernate. When Hibernate is using an application - server datasource to obtain connections enlisted with JTA, you must properly configure - the <literal>hibernate.transaction.manager_lookup_class</literal>. - </para> - </sect3> - - <sect3 id="mapping-declaration-id-uuid"> - <title>UUID algorithm</title> - <para> - The UUID contains: IP address, startup time of the JVM (accurate to a quarter - second), system time and a counter value (unique within the JVM). It's not - possible to obtain a MAC address or memory address from Java code, so this is - the best we can do without using JNI. - </para> - </sect3> - - <sect3 id="mapping-declaration-id-sequences"> - <title>Identity columns and sequences</title> - <para> - For databases which support identity columns (DB2, MySQL, Sybase, MS SQL), you - may use <literal>identity</literal> key generation. For databases that support - sequences (DB2, Oracle, PostgreSQL, Interbase, McKoi, SAP DB) you may use - <literal>sequence</literal> style key generation. Both these strategies require - two SQL queries to insert a new object. - </para> - - <programlisting><![CDATA[<id name="id" type="long" column="person_id"> - <generator class="sequence"> - <param name="sequence">person_id_sequence</param> - </generator> -</id>]]></programlisting> - - <programlisting><![CDATA[<id name="id" type="long" column="person_id" unsaved-value="0"> - <generator class="identity"/> -</id>]]></programlisting> - - <para> - For cross-platform development, the <literal>native</literal> strategy will - choose from the <literal>identity</literal>, <literal>sequence</literal> and - <literal>hilo</literal> strategies, dependant upon the capabilities of the - underlying database. - </para> - </sect3> - - <sect3 id="mapping-declaration-id-assigned"> - <title>Assigned identifiers</title> - <para> - If you want the application to assign identifiers (as opposed to having - Hibernate generate them), you may use the <literal>assigned</literal> generator. - This special generator will use the identifier value already assigned to the - object's identifier property. This generator is used when the primary key - is a natural key instead of a surrogate key. This is the default behavior - if you do no specify a <literal>&lt;generator&gt;</literal> element. - </para> - - <para> - Choosing the <literal>assigned</literal> generator makes Hibernate use - <literal>unsaved-value="undefined"</literal>, forcing Hibernate to go to - the database to determine if an instance is transient or detached, unless - there is a version or timestamp property, or you define - <literal>Interceptor.isUnsaved()</literal>. - </para> - </sect3> - - <sect3 id="mapping-declaration-id-select"> - <title>Primary keys assigned by triggers</title> - <para> - For legacy schemas only (Hibernate does not generate DDL with triggers). - </para> - - <programlisting><![CDATA[<id name="id" type="long" column="person_id"> - <generator class="select"> - <param name="key">socialSecurityNumber</param> - </generator> -</id>]]></programlisting> - - <para> - In the above example, there is a unique valued property named - <literal>socialSecurityNumber</literal> defined by the class, as a - natural key, and a surrogate key named <literal>person_id</literal> - whose value is generated by a trigger. - </para> - - </sect3> - - </sect2> - - <sect2 id="mapping-declaration-id-enhanced"> - <title>Enhanced identifier generators</title> - - <para> - Starting with release 3.2.3, there are 2 new generators which represent a re-thinking of 2 different - aspects of identifier generation. The first aspect is database portability; the second is optimization - (not having to query the database for every request for a new identifier value). These two new - generators are intended to take the place of some of the named generators described above (starting - in 3.3.x); however, they are included in the current releases and can be referenced by FQN. - </para> - - <para> - The first of these new generators is <literal>org.hibernate.id.enhanced.SequenceStyleGenerator</literal> - which is intended firstly as a replacement for the <literal>sequence</literal> generator and secondly as - a better portability generator than <literal>native</literal> (because <literal>native</literal> - (generally) chooses between <literal>identity</literal> and <literal>sequence</literal> which have - largely different semantics which can cause subtle isssues in applications eyeing portability). - <literal>org.hibernate.id.enhanced.SequenceStyleGenerator</literal> however achieves portability in - a different manner. It chooses between using a table or a sequence in the database to store its - incrementing values depending on the capabilities of the dialect being used. The difference between this - and <literal>native</literal> is that table-based and sequence-based storage have the same exact - semantic (in fact sequences are exactly what Hibernate tries to emmulate with its table-based - generators). This generator has a number of configuration parameters: - <itemizedlist spacing="compact"> - <listitem> - <para> - <literal>sequence_name</literal> (optional, defaults to <literal>hibernate_sequence</literal>): - The name of the sequence (or table) to be used. - </para> - </listitem> - <listitem> - <para> - <literal>initial_value</literal> (optional, defaults to <literal>1</literal>): The initial - value to be retrieved from the sequence/table. In sequence creation terms, this is analogous - to the clause typical named "STARTS WITH". - </para> - </listitem> - <listitem> - <para> - <literal>increment_size</literal> (optional, defaults to <literal>1</literal>): The value by - which subsequent calls to the sequence/table should differ. In sequence creation terms, this - is analogous to the clause typical named "INCREMENT BY". - </para> - </listitem> - <listitem> - <para> - <literal>force_table_use</literal> (optional, defaults to <literal>false</literal>): Should - we force the use of a table as the backing structure even though the dialect might support - sequence? - </para> - </listitem> - <listitem> - <para> - <literal>value_column</literal> (optional, defaults to <literal>next_val</literal>): Only - relevant for table structures! The name of the column on the table which is used to - hold the value. - </para> - </listitem> - <listitem> - <para> - <literal>optimizer</literal> (optional, defaults to <literal>none</literal>): - See <xref linkend="mapping-declaration-id-enhanced-optimizers"/> - </para> - </listitem> - </itemizedlist> - </para> - <para> - The second of these new generators is <literal>org.hibernate.id.enhanced.TableGenerator</literal> which - is intended firstly as a replacement for the <literal>table</literal> generator (although it actually - functions much more like <literal>org.hibernate.id.MultipleHiLoPerTableGenerator</literal>) and secondly - as a re-implementation of <literal>org.hibernate.id.MultipleHiLoPerTableGenerator</literal> utilizing the - notion of pluggable optimiziers. Essentially this generator defines a table capable of holding - a number of different increment values simultaneously by using multiple distinctly keyed rows. This - generator has a number of configuration parameters: - <itemizedlist spacing="compact"> - <listitem> - <para> - <literal>table_name</literal> (optional, defaults to <literal>hibernate_sequences</literal>): - The name of the table to be used. - </para> - </listitem> - <listitem> - <para> - <literal>value_column_name</literal> (optional, defaults to <literal>next_val</literal>): - The name of the column on the table which is used to hold the value. - </para> - </listitem> - <listitem> - <para> - <literal>segment_column_name</literal> (optional, defaults to <literal>sequence_name</literal>): - The name of the column on the table which is used to hold the "segement key". This is the - value which distinctly identifies which increment value to use. - </para> - </listitem> - <listitem> - <para> - <literal>segment_value</literal> (optional, defaults to <literal>default</literal>): - The "segment key" value for the segment from which we want to pull increment values for - this generator. - </para> - </listitem> - <listitem> - <para> - <literal>segment_value_length</literal> (optional, defaults to <literal>255</literal>): - Used for schema generation; the column size to create this segment key column. - </para> - </listitem> - <listitem> - <para> - <literal>initial_value</literal> (optional, defaults to <literal>1</literal>): - The initial value to be retrieved from the table. - </para> - </listitem> - <listitem> - <para> - <literal>increment_size</literal> (optional, defaults to <literal>1</literal>): - The value by which subsequent calls to the table should differ. - </para> - </listitem> - <listitem> - <para> - <literal>optimizer</literal> (optional, defaults to <literal></literal>): - See <xref linkend="mapping-declaration-id-enhanced-optimizers"/> - </para> - </listitem> - </itemizedlist> - </para> - </sect2> - - <sect2 id="mapping-declaration-id-enhanced-optimizers"> - <title>Identifier generator optimization</title> - <para> - For identifier generators which store values in the database, it is inefficient for them to hit the - database on each and every call to generate a new identifier value. Instead, you'd ideally want to - group a bunch of them in memory and only hit the database when you have exhausted your in-memory - value group. This is the role of the pluggable optimizers. Currently only the two enhanced generators - (<xref linkend="mapping-declaration-id-enhanced"/> support this notion. - <itemizedlist spacing="compact"> - <listitem> - <para> - <literal>none</literal> (generally this is the default if no optimizer was specified): This - says to not perform any optimizations, and hit the database each and every request. - </para> - </listitem> - <listitem> - <para> - <literal>hilo</literal>: applies a hi/lo algorithm around the database retrieved values. The - values from the database for this optimizer are expected to be sequential. The values - retrieved from the database structure for this optimizer indicates the "group number"; the - <literal>increment_size</literal> is multiplied by that value in memory to define a group - "hi value". - </para> - </listitem> - <listitem> - <para> - <literal>pooled</literal>: like was discussed for <literal>hilo</literal>, this optimizers - attempts to minimize the number of hits to the database. Here, however, we simply store - the starting value for the "next group" into the database structure rather than a sequential - value in combination with an in-memory grouping algorithm. <literal>increment_size</literal> - here refers to the values coming from the database. - </para> - </listitem> - </itemizedlist> - </para> - </sect2> - - <sect2 id="mapping-declaration-compositeid" revision="3"> - <title>composite-id</title> - - <programlisting><![CDATA[<composite-id - name="propertyName" - class="ClassName" - mapped="true|false" - access="field|property|ClassName"> - node="element-name|." - - <key-property name="propertyName" type="typename" column="column_name"/> - <key-many-to-one name="propertyName class="ClassName" column="column_name"/> - ...... -</composite-id>]]></programlisting> - - <para> - For a table with a composite key, you may map multiple properties of the class - as identifier properties. The <literal>&lt;composite-id&gt;</literal> element - accepts <literal>&lt;key-property&gt;</literal> property mappings and - <literal>&lt;key-many-to-one&gt;</literal> mappings as child elements. - </para> - - <programlisting><![CDATA[<composite-id> - <key-property name="medicareNumber"/> - <key-property name="dependent"/> -</composite-id>]]></programlisting> - - <para> - Your persistent class <emphasis>must</emphasis> override <literal>equals()</literal> - and <literal>hashCode()</literal> to implement composite identifier equality. It must - also implements <literal>Serializable</literal>. - </para> - - <para> - Unfortunately, this approach to composite identifiers means that a persistent object - is its own identifier. There is no convenient "handle" other than the object itself. - You must instantiate an instance of the persistent class itself and populate its - identifier properties before you can <literal>load()</literal> the persistent state - associated with a composite key. We call this approach an <emphasis>embedded</emphasis> - composite identifier, and discourage it for serious applications. - </para> - - <para> - A second approach is what we call a <emphasis>mapped</emphasis> composite identifier, - where the identifier properties named inside the <literal>&lt;composite-id&gt;</literal> - element are duplicated on both the persistent class and a separate identifier class. - </para> - - <programlisting><![CDATA[<composite-id class="MedicareId" mapped="true"> - <key-property name="medicareNumber"/> - <key-property name="dependent"/> -</composite-id>]]></programlisting> - - <para> - In this example, both the composite identifier class, <literal>MedicareId</literal>, - and the entity class itself have properties named <literal>medicareNumber</literal> - and <literal>dependent</literal>. The identifier class must override - <literal>equals()</literal> and <literal>hashCode()</literal> and implement. - <literal>Serializable</literal>. The disadvantage of this approach is quite - obvious&mdash;code duplication. - </para> - - <para> - The following attributes are used to specify a mapped composite identifier: - </para> - - <itemizedlist spacing="compact"> - <listitem> - <para> - <literal>mapped</literal> (optional, defaults to <literal>false</literal>): - indicates that a mapped composite identifier is used, and that the contained - property mappings refer to both the entity class and the composite identifier - class. - </para> - </listitem> - <listitem> - <para> - <literal>class</literal> (optional, but required for a mapped composite identifier): - The class used as a composite identifier. - </para> - </listitem> - </itemizedlist> - - <para> - We will describe a third, even more convenient approach where the composite identifier - is implemented as a component class in <xref linkend="components-compositeid"/>. The - attributes described below apply only to this alternative approach: - </para> - - <itemizedlist spacing="compact"> - <listitem> - <para> - <literal>name</literal> (optional, required for this approach): A property of - component type that holds the composite identifier (see chapter 9). - </para> - </listitem> - <listitem> - <para> - <literal>access</literal> (optional - defaults to <literal>property</literal>): - The strategy Hibernate should use for accessing the property value. - </para> - </listitem> - <listitem> - <para> - <literal>class</literal> (optional - defaults to the property type determined by - reflection): The component class used as a composite identifier (see next section). - </para> - </listitem> - </itemizedlist> - - <para> - This third approach, an <emphasis>identifier component</emphasis> is the one we recommend - for almost all applications. - </para> - - </sect2> - - <sect2 id="mapping-declaration-discriminator" revision="3"> - <title>discriminator</title> - - <para> - The <literal>&lt;discriminator&gt;</literal> element is required for polymorphic persistence - using the table-per-class-hierarchy mapping strategy and declares a discriminator column of the - table. The discriminator column contains marker values that tell the persistence layer what - subclass to instantiate for a particular row. A restricted set of types may be used: - <literal>string</literal>, <literal>character</literal>, <literal>integer</literal>, - <literal>byte</literal>, <literal>short</literal>, <literal>boolean</literal>, - <literal>yes_no</literal>, <literal>true_false</literal>. - </para> - - <programlistingco> - <areaspec> - <area id="discriminator1" coords="2 60"/> - <area id="discriminator2" coords="3 60" /> - <area id="discriminator3" coords="4 60" /> - <area id="discriminator4" coords="5 60" /> - <area id="discriminator5" coords="6 60" /> - </areaspec> - <programlisting><![CDATA[<discriminator - column="discriminator_column" - type="discriminator_type" - force="true|false" - insert="true|false" - formula="arbitrary sql expression" -/>]]></programlisting> - <calloutlist> - <callout arearefs="discriminator1"> - <para> - <literal>column</literal> (optional - defaults to <literal>class</literal>) the - name of the discriminator column. - </para> - </callout> - <callout arearefs="discriminator2"> - <para> - <literal>type</literal> (optional - defaults to <literal>string</literal>) a - name that indicates the Hibernate type - </para> - </callout> - <callout arearefs="discriminator3"> - <para> - <literal>force</literal> (optional - defaults to <literal>false</literal>) - "force" Hibernate to specify allowed discriminator values even when retrieving - all instances of the root class. - </para> - </callout> - <callout arearefs="discriminator4"> - <para> - <literal>insert</literal> (optional - defaults to <literal>true</literal>) - set this to <literal>false</literal> if your discriminator column is also part - of a mapped composite identifier. (Tells Hibernate to not include the column - in SQL <literal>INSERT</literal>s.) - </para> - </callout> - <callout arearefs="discriminator5"> - <para> - <literal>formula</literal> (optional) an arbitrary SQL expression that is - executed when a type has to be evaluated. Allows content-based discrimination. - </para> - </callout> - </calloutlist> - </programlistingco> - - <para> - Actual values of the discriminator column are specified by the - <literal>discriminator-value</literal> attribute of the <literal>&lt;class&gt;</literal> and - <literal>&lt;subclass&gt;</literal> elements. - </para> - - <para> - The <literal>force</literal> attribute is (only) useful if the table contains rows with - "extra" discriminator values that are not mapped to a persistent class. This will not - usually be the case. - </para> - - <para> - Using the <literal>formula</literal> attribute you can declare an arbitrary SQL expression - that will be used to evaluate the type of a row: - </para> - - <programlisting><![CDATA[<discriminator - formula="case when CLASS_TYPE in ('a', 'b', 'c') then 0 else 1 end" - type="integer"/>]]></programlisting> - - </sect2> - - <sect2 id="mapping-declaration-version" revision="4"> - <title>version (optional)</title> - - <para> - The <literal>&lt;version&gt;</literal> element is optional and indicates that - the table contains versioned data. This is particularly useful if you plan to - use <emphasis>long transactions</emphasis> (see below). - </para> - - <programlistingco> - <areaspec> - <area id="version1" coords="2 70"/> - <area id="version2" coords="3 70"/> - <area id="version3" coords="4 70"/> - <area id="version4" coords="5 70"/> - <area id="version5" coords="6 70"/> - <area id="version6" coords="7 70"/> - <area id="version7" coords="8 70"/> - </areaspec> - <programlisting><![CDATA[<version - column="version_column" - name="propertyName" - type="typename" - access="field|property|ClassName" - unsaved-value="null|negative|undefined" - generated="never|always" - insert="true|false" - node=&quot;element-name|@attribute-name|element/(a)attribute|.&quot; -/>]]></programlisting> - <calloutlist> - <callout arearefs="version1"> - <para> - <literal>column</literal> (optional - defaults to the property name): The name - of the column holding the version number. - </para> - </callout> - <callout arearefs="version2"> - <para> - <literal>name</literal>: The name of a property of the persistent class. - </para> - </callout> - <callout arearefs="version3"> - <para> - <literal>type</literal> (optional - defaults to <literal>integer</literal>): - The type of the version number. - </para> - </callout> - <callout arearefs="version4"> - <para> - <literal>access</literal> (optional - defaults to <literal>property</literal>): The - strategy Hibernate should use for accessing the property value. - </para> - </callout> - <callout arearefs="version5"> - <para> - <literal>unsaved-value</literal> (optional - defaults to <literal>undefined</literal>): - A version property value that indicates that an instance is newly instantiated - (unsaved), distinguishing it from detached instances that were saved or loaded - in a previous session. (<literal>undefined</literal> specifies that the identifier - property value should be used.) - </para> - </callout> - <callout arearefs="version6"> - <para> - <literal>generated</literal> (optional - defaults to <literal>never</literal>): - Specifies that this version property value is actually generated by the database. - See the discussion of <link linkend="mapping-generated">generated properties</link>. - </para> - </callout> - <callout arearefs="version7"> - <para> - <literal>insert</literal> (optional - defaults to <literal>true</literal>): - Specifies whether the version column should be included in SQL insert statements. - May be set to <literal>false</literal> if and only if the database column - is defined with a default value of <literal>0</literal>. - </para> - </callout> - </calloutlist> - </programlistingco> - - <para> - Version numbers may be of Hibernate type <literal>long</literal>, <literal>integer</literal>, - <literal>short</literal>, <literal>timestamp</literal> or <literal>calendar</literal>. - </para> - - <para> - A version or timestamp property should never be null for a detached instance, so - Hibernate will detect any instance with a null version or timestamp as transient, - no matter what other <literal>unsaved-value</literal> strategies are specified. - <emphasis>Declaring a nullable version or timestamp property is an easy way to avoid - any problems with transitive reattachment in Hibernate, especially useful for people - using assigned identifiers or composite keys!</emphasis> - </para> - </sect2> - - <sect2 id="mapping-declaration-timestamp" revision="4" > - <title>timestamp (optional)</title> - - <para> - The optional <literal>&lt;timestamp&gt;</literal> element indicates that the table contains - timestamped data. This is intended as an alternative to versioning. Timestamps are by nature - a less safe implementation of optimistic locking. However, sometimes the application might - use the timestamps in other ways. - </para> - - <programlistingco> - <areaspec> - <area id="timestamp1" coords="2 70"/> - <area id="timestamp2" coords="3 70" /> - <area id="timestamp3" coords="4 70" /> - <area id="timestamp4" coords="5 70" /> - <area id="timestamp5" coords="6 70" /> - <area id="timestamp6" coords="7 70" /> - </areaspec> - <programlisting><![CDATA[<timestamp - column="timestamp_column" - name="propertyName" - access="field|property|ClassName" - unsaved-value="null|undefined" - source="vm|db" - generated="never|always" - node=&quot;element-name|@attribute-name|element/(a)attribute|.&quot; -/>]]></programlisting> - <calloutlist> - <callout arearefs="timestamp1"> - <para> - <literal>column</literal> (optional - defaults to the property name): The name - of a column holding the timestamp. - </para> - </callout> - <callout arearefs="timestamp2"> - <para> - <literal>name</literal>: The name of a JavaBeans style property of - Java type <literal>Date</literal> or <literal>Timestamp</literal> of the - persistent class. - </para> - </callout> - <callout arearefs="timestamp3"> - <para> - <literal>access</literal> (optional - defaults to <literal>property</literal>): The - strategy Hibernate should use for accessing the property value. - </para> - </callout> - <callout arearefs="timestamp4"> - <para> - <literal>unsaved-value</literal> (optional - defaults to <literal>null</literal>): - A version property value that indicates that an instance is newly instantiated - (unsaved), distinguishing it from detached instances that were saved or loaded - in a previous session. (<literal>undefined</literal> specifies that the identifier - property value should be used.) - </para> - </callout> - <callout arearefs="timestamp5"> - <para> - <literal>source</literal> (optional - defaults to <literal>vm</literal>): - From where should Hibernate retrieve the timestamp value? From the database, - or from the current JVM? Database-based timestamps incur an overhead because - Hibernate must hit the database in order to determine the "next value", - but will be safer for use in clustered environments. Note also, that not - all <literal>Dialect</literal>s are known to support retrieving of the - database's current timestamp, while others might be unsafe for usage - in locking due to lack of precision (Oracle 8 for example). - </para> - </callout> - <callout arearefs="timestamp6"> - <para> - <literal>generated</literal> (optional - defaults to <literal>never</literal>): - Specifies that this timestamp property value is actually generated by the database. - See the discussion of <link linkend="mapping-generated">generated properties</link>. - </para> - </callout> - </calloutlist> - </programlistingco> - - <para> - Note that <literal>&lt;timestamp&gt;</literal> is equivalent to - <literal>&lt;version type="timestamp"&gt;</literal>. And - <literal>&lt;timestamp source="db"&gt;</literal> is equivalent to - <literal>&lt;version type="dbtimestamp"&gt;</literal> - </para> - </sect2> - - - <sect2 id="mapping-declaration-property" revision="4"> - <title>property</title> - - <para> - The <literal>&lt;property&gt;</literal> element declares a persistent, JavaBean style - property of the class. - </para> - - <programlistingco> - <areaspec> - <area id="property1" coords="2 70"/> - <area id="property2" coords="3 70"/> - <area id="property3" coords="4 70"/> - <areaset id="property4-5" coords=""> - <area id="property4" coords='5 70'/> - <area id="property5" coords='6 70'/> - </areaset> - <area id="property6" coords="7 70"/> - <area id="property7" coords="8 70"/> - <area id="property8" coords="9 70"/> - <area id="property9" coords="10 70"/> - <area id="property10" coords="11 70"/> - <area id="property11" coords="12 70"/> - <area id="property12" coords="13 70"/> - </areaspec> - <programlisting><![CDATA[<property - name="propertyName" - column="column_name" - type="typename" - update="true|false" - insert="true|false" - formula="arbitrary SQL expression" - access="field|property|ClassName" - lazy="true|false" - unique="true|false" - not-null="true|false" - optimistic-lock="true|false" - generated="never|insert|always" - node=&quot;element-name|@attribute-name|element/(a)attribute|.&quot; - index="index_name" - unique_key="unique_key_id" - length="L" - precision="P" - scale="S" -/>]]></programlisting> - <calloutlist> - <callout arearefs="property1"> - <para> - <literal>name</literal>: the name of the property, with an initial lowercase - letter. - </para> - </callout> - <callout arearefs="property2"> - <para> - <literal>column</literal> (optional - defaults to the property name): the name - of the mapped database table column. This may also be specified by nested - <literal>&lt;column&gt;</literal> element(s). - </para> - </callout> - <callout arearefs="property3"> - <para> - <literal>type</literal> (optional): a name that indicates the Hibernate type. - </para> - </callout> - <callout arearefs="property4-5"> - <para> - <literal>update, insert</literal> (optional - defaults to <literal>true</literal>) : - specifies that the mapped columns should be included in SQL <literal>UPDATE</literal> - and/or <literal>INSERT</literal> statements. Setting both to <literal>false</literal> - allows a pure "derived" property whose value is initialized from some other - property that maps to the same colum(s) or by a trigger or other application. - </para> - </callout> - <callout arearefs="property6"> - <para> - <literal>formula</literal> (optional): an SQL expression that defines the value for a - <emphasis>computed</emphasis> property. Computed properties do not have a column - mapping of their own. - </para> - </callout> - <callout arearefs="property7"> - <para> - <literal>access</literal> (optional - defaults to <literal>property</literal>): The - strategy Hibernate should use for accessing the property value. - </para> - </callout> - <callout arearefs="property8"> - <para> - <literal>lazy</literal> (optional - defaults to <literal>false</literal>): Specifies - that this property should be fetched lazily when the instance variable is first - accessed (requires build-time bytecode instrumentation). - </para> - </callout> - <callout arearefs="property9"> - <para> - <literal>unique</literal> (optional): Enable the DDL generation of a unique - constraint for the columns. Also, allow this to be the target of - a <literal>property-ref</literal>. - </para> - </callout> - <callout arearefs="property10"> - <para> - <literal>not-null</literal> (optional): Enable the DDL generation of a nullability - constraint for the columns. - </para> - </callout> - <callout arearefs="property11"> - <para> - <literal>optimistic-lock</literal> (optional - defaults to <literal>true</literal>): - Specifies that updates to this property do or do not require acquisition of the - optimistic lock. In other words, determines if a version increment should occur when - this property is dirty. - </para> - </callout> - <callout arearefs="property12"> - <para> - <literal>generated</literal> (optional - defaults to <literal>never</literal>): - Specifies that this property value is actually generated by the database. - See the discussion of <link linkend="mapping-generated">generated properties</link>. - </para> - </callout> - </calloutlist> - </programlistingco> - - <para> - <emphasis>typename</emphasis> could be: - </para> - - <orderedlist spacing="compact"> - <listitem> - <para> - The name of a Hibernate basic type (eg. <literal>integer, string, character, - date, timestamp, float, binary, serializable, object, blob</literal>). - </para> - </listitem> - <listitem> - <para> - The name of a Java class with a default basic type (eg. <literal>int, float, - char, java.lang.String, java.util.Date, java.lang.Integer, java.sql.Clob</literal>). - </para> - </listitem> - <listitem> - <para> - The name of a serializable Java class. - </para> - </listitem> - <listitem> - <para> - The class name of a custom type (eg. <literal>com.illflow.type.MyCustomType</literal>). - </para> - </listitem> - </orderedlist> - - <para> - If you do not specify a type, Hibernate will use reflection upon the named - property to take a guess at the correct Hibernate type. Hibernate will try to - interpret the name of the return class of the property getter using rules 2, 3, - 4 in that order. However, this is not always enough. - In certain cases you will still need the <literal>type</literal> - attribute. (For example, to distinguish between <literal>Hibernate.DATE</literal> and - <literal>Hibernate.TIMESTAMP</literal>, or to specify a custom type.) - </para> - - <para> - The <literal>access</literal> attribute lets you control how Hibernate will access - the property at runtime. By default, Hibernate will call the property get/set pair. - If you specify <literal>access="field"</literal>, Hibernate will bypass the get/set - pair and access the field directly, using reflection. You may specify your own - strategy for property access by naming a class that implements the interface - <literal>org.hibernate.property.PropertyAccessor</literal>. - </para> - - <para> - An especially powerful feature are derived properties. These properties are by - definition read-only, the property value is computed at load time. You declare - the computation as a SQL expression, this translates to a <literal>SELECT</literal> - clause subquery in the SQL query that loads an instance: - </para> - - <programlisting><![CDATA[ -<property name="totalPrice" - formula="( SELECT SUM (li.quantity*p.price) FROM LineItem li, Product p - WHERE li.productId = p.productId - AND li.customerId = customerId - AND li.orderNumber = orderNumber )"/>]]></programlisting> - - <para> - Note that you can reference the entities own table by not declaring an alias on - a particular column (<literal>customerId</literal> in the given example). Also note - that you can use the nested <literal>&lt;formula&gt;</literal> mapping element - if you don't like to use the attribute. - </para> - - </sect2> - - <sect2 id="mapping-declaration-manytoone" revision="5"> - <title>many-to-one</title> - - <para> - An ordinary association to another persistent class is declared using a - <literal>many-to-one</literal> element. The relational model is a - many-to-one association: a foreign key in one table is referencing - the primary key column(s) of the target table. - </para> - - <programlistingco> - <areaspec> - <area id="manytoone1" coords="2 70"/> - <area id="manytoone2" coords="3 70"/> - <area id="manytoone3" coords="4 70"/> - <area id="manytoone4" coords="5 70"/> - <area id="manytoone5" coords="6 70"/> - <areaset id="manytoone6-7" coords=""> - <area id="manytoone6" coords='7 70'/> - <area id="manytoone7" coords='8 70'/> - </areaset> - <area id="manytoone8" coords="9 70"/> - <area id="manytoone9" coords="10 70"/> - <area id="manytoone10" coords="11 70"/> - <area id="manytoone11" coords="12 70"/> - <area id="manytoone12" coords="13 70"/> - <area id="manytoone13" coords="14 70"/> - <area id="manytoone14" coords="15 70"/> - <area id="manytoone15" coords="16 70"/> - <area id="manytoone16" coords="17 70"/> - </areaspec> - <programlisting><![CDATA[<many-to-one - name="propertyName" - column="column_name" - class="ClassName" - cascade="cascade_style" - fetch="join|select" - update="true|false" - insert="true|false" - property-ref="propertyNameFromAssociatedClass" - access="field|property|ClassName" - unique="true|false" - not-null="true|false" - optimistic-lock="true|false" - lazy="proxy|no-proxy|false" - not-found="ignore|exception" - entity-name="EntityName" - formula="arbitrary SQL expression" - node=&quot;element-name|@attribute-name|element/(a)attribute|.&quot; - embed-xml="true|false" - index="index_name" - unique_key="unique_key_id" - foreign-key="foreign_key_name" -/>]]></programlisting> - <calloutlist> - <callout arearefs="manytoone1"> - <para> - <literal>name</literal>: The name of the property. - </para> - </callout> - <callout arearefs="manytoone2"> - <para> - <literal>column</literal> (optional): The name of the foreign key column. - This may also be specified by nested <literal>&lt;column&gt;</literal> - element(s). - </para> - </callout> - <callout arearefs="manytoone3"> - <para> - <literal>class</literal> (optional - defaults to the property type - determined by reflection): The name of the associated class. - </para> - </callout> - <callout arearefs="manytoone4"> - <para> - <literal>cascade</literal> (optional): Specifies which operations should - be cascaded from the parent object to the associated object. - </para> - </callout> - <callout arearefs="manytoone5"> - <para> - <literal>fetch</literal> (optional - defaults to <literal>select</literal>): - Chooses between outer-join fetching or sequential select fetching. - </para> - </callout> - <callout arearefs="manytoone6-7"> - <para> - <literal>update, insert</literal> (optional - defaults to <literal>true</literal>) - specifies that the mapped columns should be included in SQL <literal>UPDATE</literal> - and/or <literal>INSERT</literal> statements. Setting both to <literal>false</literal> - allows a pure "derived" association whose value is initialized from some other - property that maps to the same colum(s) or by a trigger or other application. - </para> - </callout> - <callout arearefs="manytoone8"> - <para> - <literal>property-ref</literal>: (optional) The name of a property of the associated - class that is joined to this foreign key. If not specified, the primary key of - the associated class is used. - </para> - </callout> - <callout arearefs="manytoone9"> - <para> - <literal>access</literal> (optional - defaults to <literal>property</literal>): The - strategy Hibernate should use for accessing the property value. - </para> - </callout> - <callout arearefs="manytoone10"> - <para> - <literal>unique</literal> (optional): Enable the DDL generation of a unique - constraint for the foreign-key column. Also, allow this to be the target of - a <literal>property-ref</literal>. This makes the association multiplicity - effectively one to one. - </para> - </callout> - <callout arearefs="manytoone11"> - <para> - <literal>not-null</literal> (optional): Enable the DDL generation of a nullability - constraint for the foreign key columns. - </para> - </callout> - <callout arearefs="manytoone12"> - <para> - <literal>optimistic-lock</literal> (optional - defaults to <literal>true</literal>): - Specifies that updates to this property do or do not require acquisition of the - optimistic lock. In other words, dertermines if a version increment should occur when - this property is dirty. - </para> - </callout> - <callout arearefs="manytoone13"> - <para> - <literal>lazy</literal> (optional - defaults to <literal>proxy</literal>): - By default, single point associations are proxied. <literal>lazy="no-proxy"</literal> - specifies that the property should be fetched lazily when the instance variable - is first accessed (requires build-time bytecode instrumentation). - <literal>lazy="false"</literal> specifies that the association will always - be eagerly fetched. - </para> - </callout> - <callout arearefs="manytoone14"> - <para> - <literal>not-found</literal> (optional - defaults to <literal>exception</literal>): - Specifies how foreign keys that reference missing rows will be handled: - <literal>ignore</literal> will treat a missing row as a null association. - </para> - </callout> - <callout arearefs="manytoone15"> - <para> - <literal>entity-name</literal> (optional): The entity name of the associated class. - </para> - </callout> - <callout arearefs="manytoone16"> - <para> - <literal>formula</literal> (optional): an SQL expression that defines the value for a - <emphasis>computed</emphasis> foreign key. - </para> - </callout> - </calloutlist> - </programlistingco> - - <para> - Setting a value of the <literal>cascade</literal> attribute to any meaningful - value other than <literal>none</literal> will propagate certain operations to the - associated object. The meaningful values are the names of Hibernate's basic - operations, <literal>persist, merge, delete, save-update, evict, replicate, lock, - refresh</literal>, as well as the special values <literal>delete-orphan</literal> - and <literal>all</literal> and comma-separated combinations of operation - names, for example, <literal>cascade="persist,merge,evict"</literal> or - <literal>cascade="all,delete-orphan"</literal>. See <xref linkend="objectstate-transitive"/> - for a full explanation. Note that single valued associations (many-to-one and - one-to-one associations) do not support orphan delete. - </para> - - <para> - A typical <literal>many-to-one</literal> declaration looks as simple as this: - </para> - - <programlisting><![CDATA[<many-to-one name="product" class="Product" column="PRODUCT_ID"/>]]></programlisting> - - <para> - The <literal>property-ref</literal> attribute should only be used for mapping legacy - data where a foreign key refers to a unique key of the associated table other than - the primary key. This is an ugly relational model. For example, suppose the - <literal>Product</literal> class had a unique serial number, that is not the primary - key. (The <literal>unique</literal> attribute controls Hibernate's DDL generation with - the SchemaExport tool.) - </para> - - <programlisting><![CDATA[<property name="serialNumber" unique="true" type="string" column="SERIAL_NUMBER"/>]]></programlisting> - - <para> - Then the mapping for <literal>OrderItem</literal> might use: - </para> - - <programlisting><![CDATA[<many-to-one name="product" property-ref="serialNumber" column="PRODUCT_SERIAL_NUMBER"/>]]></programlisting> - - <para> - This is certainly not encouraged, however. - </para> - - <para> - If the referenced unique key comprises multiple properties of the associated entity, you should - map the referenced properties inside a named <literal>&lt;properties&gt;</literal> element. - </para> - - <para> - If the referenced unique key is the property of a component, you may specify a property path: - </para> - - <programlisting><![CDATA[<many-to-one name="owner" property-ref="identity.ssn" column="OWNER_SSN"/>]]></programlisting> - - </sect2> - - <sect2 id="mapping-declaration-onetoone" revision="3"> - <title>one-to-one</title> - - <para> - A one-to-one association to another persistent class is declared using a - <literal>one-to-one</literal> element. - </para> - - <programlistingco> - <areaspec> - <area id="onetoone1" coords="2 70"/> - <area id="onetoone2" coords="3 70"/> - <area id="onetoone3" coords="4 70"/> - <area id="onetoone4" coords="5 70"/> - <area id="onetoone5" coords="6 70"/> - <area id="onetoone6" coords="7 70"/> - <area id="onetoone7" coords="8 70"/> - <area id="onetoone8" coords="9 70"/> - <area id="onetoone9" coords="10 70"/> - <area id="onetoone10" coords="11 70"/> - </areaspec> - <programlisting><![CDATA[<one-to-one - name="propertyName" - class="ClassName" - cascade="cascade_style" - constrained="true|false" - fetch="join|select" - property-ref="propertyNameFromAssociatedClass" - access="field|property|ClassName" - formula="any SQL expression" - lazy="proxy|no-proxy|false" - entity-name="EntityName" - node=&quot;element-name|@attribute-name|element/(a)attribute|.&quot; - embed-xml="true|false" - foreign-key="foreign_key_name" -/>]]></programlisting> - <calloutlist> - <callout arearefs="onetoone1"> - <para> - <literal>name</literal>: The name of the property. - </para> - </callout> - <callout arearefs="onetoone2"> - <para> - <literal>class</literal> (optional - defaults to the property type - determined by reflection): The name of the associated class. - </para> - </callout> - <callout arearefs="onetoone3"> - <para> - <literal>cascade</literal> (optional) specifies which operations should - be cascaded from the parent object to the associated object. - </para> - </callout> - <callout arearefs="onetoone4"> - <para> - <literal>constrained</literal> (optional) specifies that a foreign key constraint - on the primary key of the mapped table references the table of the associated - class. This option affects the order in which <literal>save()</literal> and - <literal>delete()</literal> are cascaded, and determines whether the association - may be proxied (it is also used by the schema export tool). - </para> - </callout> - <callout arearefs="onetoone5"> - <para> - <literal>fetch</literal> (optional - defaults to <literal>select</literal>): - Chooses between outer-join fetching or sequential select fetching. - </para> - </callout> - <callout arearefs="onetoone6"> - <para> - <literal>property-ref</literal>: (optional) The name of a property of the associated class - that is joined to the primary key of this class. If not specified, the primary key of - the associated class is used. - </para> - </callout> - <callout arearefs="onetoone7"> - <para> - <literal>access</literal> (optional - defaults to <literal>property</literal>): The - strategy Hibernate should use for accessing the property value. - </para> - </callout> - <callout arearefs="onetoone8"> - <para> - <literal>formula</literal> (optional): Almost all one to one associations map to the - primary key of the owning entity. In the rare case that this is not the case, you may - specify a some other column, columns or expression to join on using an SQL formula. (See - <literal>org.hibernate.test.onetooneformula</literal> for an example.) - </para> - </callout> - <callout arearefs="onetoone9"> - <para> - <literal>lazy</literal> (optional - defaults to <literal>proxy</literal>): - By default, single point associations are proxied. <literal>lazy="no-proxy"</literal> - specifies that the property should be fetched lazily when the instance variable - is first accessed (requires build-time bytecode instrumentation). - <literal>lazy="false"</literal> specifies that the association will always - be eagerly fetched. <emphasis>Note that if <literal>constrained="false"</literal>, - proxying is impossible and Hibernate will eager fetch the association!</emphasis> - </para> - </callout> - <callout arearefs="onetoone10"> - <para> - <literal>entity-name</literal> (optional): The entity name of the associated class. - </para> - </callout> - </calloutlist> - </programlistingco> - - <para> - There are two varieties of one-to-one association: - </para> - <itemizedlist> - <listitem><para> - primary key associations - </para></listitem> - <listitem><para> - unique foreign key associations - </para></listitem> - </itemizedlist> - - <para> - Primary key associations don't need an extra table column; if two rows are related by - the association then the two table rows share the same primary key value. So if you want - two objects to be related by a primary key association, you must make sure that they - are assigned the same identifier value! - </para> - - <para> - For a primary key association, add the following mappings to <literal>Employee</literal> and - <literal>Person</literal>, respectively. - </para> - - <programlisting><![CDATA[<one-to-one name="person" class="Person"/>]]></programlisting> - <programlisting><![CDATA[<one-to-one name="employee" class="Employee" constrained="true"/>]]></programlisting> - - <para> - Now we must ensure that the primary keys of related rows in the PERSON and - EMPLOYEE tables are equal. We use a special Hibernate identifier generation strategy - called <literal>foreign</literal>: - </para> - - <programlisting><![CDATA[<class name="person" table="PERSON"> - <id name="id" column="PERSON_ID"> - <generator class="foreign"> - <param name="property">employee</param> - </generator> - </id> - ... - <one-to-one name="employee" - class="Employee" - constrained="true"/> -</class>]]></programlisting> - - <para> - A newly saved instance of <literal>Person</literal> is then assigned the same primary - key value as the <literal>Employee</literal> instance refered with the <literal>employee</literal> - property of that <literal>Person</literal>. - </para> - - <para> - Alternatively, a foreign key with a unique constraint, from <literal>Employee</literal> to - <literal>Person</literal>, may be expressed as: - </para> - - <programlisting><![CDATA[<many-to-one name="person" class="Person" column="PERSON_ID" unique="true"/>]]></programlisting> - - <para> - And this association may be made bidirectional by adding the following to the - <literal>Person</literal> mapping: - </para> - - <programlisting><![CDATA[<one-to-one name="employee" class="Employee" property-ref="person"/>]]></programlisting> - - </sect2> - - <sect2 id="mapping-declaration-naturalid"> - <title>natural-id</title> - - <programlisting><![CDATA[<natural-id mutable="true|false"/> - <property ... /> - <many-to-one ... /> - ...... -</natural-id>]]></programlisting> - - <para> - Even though we recommend the use of surrogate keys as primary keys, you should still try - to identify natural keys for all entities. A natural key is a property or combination of - properties that is unique and non-null. If it is also immutable, even better. Map the - properties of the natural key inside the <literal>&lt;natural-id&gt;</literal> element. - Hibernate will generate the necessary unique key and nullability constraints, and your - mapping will be more self-documenting. - </para> - - <para> - We strongly recommend that you implement <literal>equals()</literal> and - <literal>hashCode()</literal> to compare the natural key properties of the entity. - </para> - - <para> - This mapping is not intended for use with entities with natural primary keys. - </para> - - <itemizedlist spacing="compact"> - <listitem> - <para> - <literal>mutable</literal> (optional, defaults to <literal>false</literal>): - By default, natural identifier properties as assumed to be immutable (constant). - </para> - </listitem> - </itemizedlist> - - </sect2> - - <sect2 id="mapping-declaration-component" revision="2"> - <title>component, dynamic-component</title> - - <para> - The <literal>&lt;component&gt;</literal> element maps properties of a - child object to columns of the table of a parent class. Components may, in - turn, declare their own properties, components or collections. See - "Components" below. - </para> - - <programlistingco> - <areaspec> - <area id="component1" coords="2 45"/> - <area id="component2" coords="3 45"/> - <area id="component3" coords="4 45"/> - <area id="component4" coords="5 45"/> - <area id="component5" coords="6 45"/> - <area id="component6" coords="7 45"/> - <area id="component7" coords="8 45"/> - <area id="component8" coords="9 45"/> - </areaspec> - <programlisting><![CDATA[<component - name="propertyName" - class="className" - insert="true|false" - update="true|false" - access="field|property|ClassName" - lazy="true|false" - optimistic-lock="true|false" - unique="true|false" - node="element-name|." -> - - <property ...../> - <many-to-one .... /> - ........ -</component>]]></programlisting> - <calloutlist> - <callout arearefs="component1"> - <para> - <literal>name</literal>: The name of the property. - </para> - </callout> - <callout arearefs="component2"> - <para> - <literal>class</literal> (optional - defaults to the property type - determined by reflection): The name of the component (child) class. - </para> - </callout> - <callout arearefs="component3"> - <para> - <literal>insert</literal>: Do the mapped columns appear in SQL - <literal>INSERT</literal>s? - </para> - </callout> - <callout arearefs="component4"> - <para> - <literal>update</literal>: Do the mapped columns appear in SQL - <literal>UPDATE</literal>s? - </para> - </callout> - <callout arearefs="component5"> - <para> - <literal>access</literal> (optional - defaults to <literal>property</literal>): The - strategy Hibernate should use for accessing the property value. - </para> - </callout> - <callout arearefs="component6"> - <para> - <literal>lazy</literal> (optional - defaults to <literal>false</literal>): Specifies - that this component should be fetched lazily when the instance variable is first - accessed (requires build-time bytecode instrumentation). - </para> - </callout> - <callout arearefs="component7"> - <para> - <literal>optimistic-lock</literal> (optional - defaults to <literal>true</literal>): - Specifies that updates to this component do or do not require acquisition of the - optimistic lock. In other words, determines if a version increment should occur when - this property is dirty. - </para> - </callout> - <callout arearefs="component8"> - <para> - <literal>unique</literal> (optional - defaults to <literal>false</literal>): - Specifies that a unique constraint exists upon all mapped columns of the - component. - </para> - </callout> - </calloutlist> - </programlistingco> - - <para> - The child <literal>&lt;property&gt;</literal> tags map properties of the - child class to table columns. - </para> - - <para> - The <literal>&lt;component&gt;</literal> element allows a <literal>&lt;parent&gt;</literal> - subelement that maps a property of the component class as a reference back to the - containing entity. - </para> - - <para> - The <literal>&lt;dynamic-component&gt;</literal> element allows a <literal>Map</literal> - to be mapped as a component, where the property names refer to keys of the map, see - <xref linkend="components-dynamic"/>. - </para> - - </sect2> - - <sect2 id="mapping-declaration-properties" revision="2"> - <title>properties</title> - - <para> - The <literal>&lt;properties&gt;</literal> element allows the definition of a named, - logical grouping of properties of a class. The most important use of the construct - is that it allows a combination of properties to be the target of a - <literal>property-ref</literal>. It is also a convenient way to define a multi-column - unique constraint. - </para> - - <programlistingco> - <areaspec> - <area id="properties1" coords="2 45"/> - <area id="properties2" coords="3 45"/> - <area id="properties3" coords="4 45"/> - <area id="properties4" coords="5 45"/> - <area id="properties5" coords="6 45"/> - </areaspec> - <programlisting><![CDATA[<properties - name="logicalName" - insert="true|false" - update="true|false" - optimistic-lock="true|false" - unique="true|false" -> - - <property ...../> - <many-to-one .... /> - ........ -</properties>]]></programlisting> - <calloutlist> - <callout arearefs="properties1"> - <para> - <literal>name</literal>: The logical name of the grouping - - <emphasis>not</emphasis> an actual property name. - </para> - </callout> - <callout arearefs="properties2"> - <para> - <literal>insert</literal>: Do the mapped columns appear in SQL - <literal>INSERT</literal>s? - </para> - </callout> - <callout arearefs="properties3"> - <para> - <literal>update</literal>: Do the mapped columns appear in SQL - <literal>UPDATE</literal>s? - </para> - </callout> - <callout arearefs="properties4"> - <para> - <literal>optimistic-lock</literal> (optional - defaults to <literal>true</literal>): - Specifies that updates to these properties do or do not require acquisition of the - optimistic lock. In other words, determines if a version increment should occur when - these properties are dirty. - </para> - </callout> - <callout arearefs="properties5"> - <para> - <literal>unique</literal> (optional - defaults to <literal>false</literal>): - Specifies that a unique constraint exists upon all mapped columns of the - component. - </para> - </callout> - </calloutlist> - </programlistingco> - - <para> - For example, if we have the following <literal>&lt;properties&gt;</literal> mapping: - </para> - - <programlisting><![CDATA[<class name="Person"> - <id name="personNumber"/> - ... - <properties name="name" - unique="true" update="false"> - <property name="firstName"/> - <property name="initial"/> - <property name="lastName"/> - </properties> -</class>]]></programlisting> - - <para> - Then we might have some legacy data association which refers to this unique key of - the <literal>Person</literal> table, instead of to the primary key: - </para> - - <programlisting><![CDATA[<many-to-one name="person" - class="Person" property-ref="name"> - <column name="firstName"/> - <column name="initial"/> - <column name="lastName"/> -</many-to-one>]]></programlisting> - - <para> - We don't recommend the use of this kind of thing outside the context of mapping - legacy data. - </para> - - </sect2> - - <sect2 id="mapping-declaration-subclass" revision="4"> - <title>subclass</title> - - <para> - Finally, polymorphic persistence requires the declaration of each subclass of - the root persistent class. For the table-per-class-hierarchy - mapping strategy, the <literal>&lt;subclass&gt;</literal> declaration is used. - </para> - - <programlistingco> - <areaspec> - <area id="subclass1" coords="2 55"/> - <area id="subclass2" coords="3 55"/> - <area id="subclass3" coords="4 55"/> - <area id="subclass4" coords="5 55"/> - </areaspec> - <programlisting><![CDATA[<subclass - name="ClassName" - discriminator-value="discriminator_value" - proxy="ProxyInterface" - lazy="true|false" - dynamic-update="true|false" - dynamic-insert="true|false" - entity-name="EntityName" - node="element-name" - extends="SuperclassName"> - - <property .... /> - ..... -</subclass>]]></programlisting> - <calloutlist> - <callout arearefs="subclass1"> - <para> - <literal>name</literal>: The fully qualified class name of the subclass. - </para> - </callout> - <callout arearefs="subclass2"> - <para> - <literal>discriminator-value</literal> (optional - defaults to the class name): A - value that distiguishes individual subclasses. - </para> - </callout> - <callout arearefs="subclass3"> - <para> - <literal>proxy</literal> (optional): Specifies a class or interface to use for - lazy initializing proxies. - </para> - </callout> - <callout arearefs="subclass4"> - <para> - <literal>lazy</literal> (optional, defaults to <literal>true</literal>): Setting - <literal>lazy="false"</literal> disables the use of lazy fetching. - </para> - </callout> - </calloutlist> - </programlistingco> - - <para> - Each subclass should declare its own persistent properties and subclasses. - <literal>&lt;version&gt;</literal> and <literal>&lt;id&gt;</literal> properties - are assumed to be inherited from the root class. Each subclass in a heirarchy must - define a unique <literal>discriminator-value</literal>. If none is specified, the - fully qualified Java class name is used. - </para> - - <para> - For information about inheritance mappings, see <xref linkend="inheritance"/>. - </para> - - </sect2> - - <sect2 id="mapping-declaration-joinedsubclass" revision="3"> - <title>joined-subclass</title> - - <para> - Alternatively, each subclass may be mapped to its own table (table-per-subclass - mapping strategy). Inherited state is retrieved by joining with the table of the - superclass. We use the <literal>&lt;joined-subclass&gt;</literal> element. - </para> - - <programlistingco> - <areaspec> - <area id="joinedsubclass1" coords="2 45"/> - <area id="joinedsubclass2" coords="3 45"/> - <area id="joinedsubclass3" coords="4 45"/> - <area id="joinedsubclass4" coords="5 45"/> - </areaspec> - <programlisting><![CDATA[<joined-subclass - name="ClassName" - table="tablename" - proxy="ProxyInterface" - lazy="true|false" - dynamic-update="true|false" - dynamic-insert="true|false" - schema="schema" - catalog="catalog" - extends="SuperclassName" - persister="ClassName" - subselect="SQL expression" - entity-name="EntityName" - node="element-name"> - - <key .... > - - <property .... /> - ..... -</joined-subclass>]]></programlisting> - <calloutlist> - <callout arearefs="joinedsubclass1"> - <para> - <literal>name</literal>: The fully qualified class name of the subclass. - </para> - </callout> - <callout arearefs="joinedsubclass2"> - <para> - <literal>table</literal>: The name of the subclass table. - </para> - </callout> - <callout arearefs="joinedsubclass3"> - <para> - <literal>proxy</literal> (optional): Specifies a class or interface to use - for lazy initializing proxies. - </para> - </callout> - <callout arearefs="joinedsubclass4"> - <para> - <literal>lazy</literal> (optional, defaults to <literal>true</literal>): Setting - <literal>lazy="false"</literal> disables the use of lazy fetching. - </para> - </callout> - </calloutlist> - </programlistingco> - - <para> - No discriminator column is required for this mapping strategy. Each subclass must, - however, declare a table column holding the object identifier using the - <literal>&lt;key&gt;</literal> element. The mapping at the start of the chapter - would be re-written as: - </para> - - <programlisting><![CDATA[<?xml version="1.0"?> -<!DOCTYPE hibernate-mapping PUBLIC - "-//Hibernate/Hibernate Mapping DTD//EN" - "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> - -<hibernate-mapping package="eg"> - - <class name="Cat" table="CATS"> - <id name="id" column="uid" type="long"> - <generator class="hilo"/> - </id> - <property name="birthdate" type="date"/> - <property name="color" not-null="true"/> - <property name="sex" not-null="true"/> - <property name="weight"/> - <many-to-one name="mate"/> - <set name="kittens"> - <key column="MOTHER"/> - <one-to-many class="Cat"/> - </set> - <joined-subclass name="DomesticCat" table="DOMESTIC_CATS"> - <key column="CAT"/> - <property name="name" type="string"/> - </joined-subclass> - </class> - - <class name="eg.Dog"> - <!-- mapping for Dog could go here --> - </class> - -</hibernate-mapping>]]></programlisting> - - <para> - For information about inheritance mappings, see <xref linkend="inheritance"/>. - </para> - - </sect2> - - <sect2 id="mapping-declaration-unionsubclass" revision="2"> - <title>union-subclass</title> - - <para> - A third option is to map only the concrete classes of an inheritance hierarchy - to tables, (the table-per-concrete-class strategy) where each table defines all - persistent state of the class, including inherited state. In Hibernate, it is - not absolutely necessary to explicitly map such inheritance hierarchies. You - can simply map each class with a separate <literal>&lt;class&gt;</literal> - declaration. However, if you wish use polymorphic associations (e.g. an association - to the superclass of your hierarchy), you need to - use the <literal>&lt;union-subclass&gt;</literal> mapping. - </para> - - <programlistingco> - <areaspec> - <area id="unionsubclass1" coords="2 45"/> - <area id="unionsubclass2" coords="3 45"/> - <area id="unionsubclass3" coords="4 45"/> - <area id="unionsubclass4" coords="5 45"/> - </areaspec> - <programlisting><![CDATA[<union-subclass - name="ClassName" - table="tablename" - proxy="ProxyInterface" - lazy="true|false" - dynamic-update="true|false" - dynamic-insert="true|false" - schema="schema" - catalog="catalog" - extends="SuperclassName" - abstract="true|false" - persister="ClassName" - subselect="SQL expression" - entity-name="EntityName" - node="element-name"> - - <property .... /> - ..... -</union-subclass>]]></programlisting> - <calloutlist> - <callout arearefs="unionsubclass1"> - <para> - <literal>name</literal>: The fully qualified class name of the subclass. - </para> - </callout> - <callout arearefs="unionsubclass2"> - <para> - <literal>table</literal>: The name of the subclass table. - </para> - </callout> - <callout arearefs="unionsubclass3"> - <para> - <literal>proxy</literal> (optional): Specifies a class or interface to use - for lazy initializing proxies. - </para> - </callout> - <callout arearefs="unionsubclass4"> - <para> - <literal>lazy</literal> (optional, defaults to <literal>true</literal>): Setting - <literal>lazy="false"</literal> disables the use of lazy fetching. - </para> - </callout> - </calloutlist> - </programlistingco> - - <para> - No discriminator column or key column is required for this mapping strategy. - </para> - - <para> - For information about inheritance mappings, see <xref linkend="inheritance"/>. - </para> - - </sect2> - - <sect2 id="mapping-declaration-join" revision="3"> - <title>join</title> - - <para> - Using the <literal>&lt;join&gt;</literal> element, it is possible to map - properties of one class to several tables, when there's a 1-to-1 relationship between the tables. - </para> - - <programlistingco> - <areaspec> - <area id="join1" coords="2 50"/> - <area id="join2" coords="3 50"/> - <area id="join3" coords="4 50"/> - <area id="join4" coords="5 50"/> - <area id="join5" coords="6 50"/> - <area id="join6" coords="7 50"/> - </areaspec> - <programlisting><![CDATA[<join - table="tablename" - schema="owner" - catalog="catalog" - fetch="join|select" - inverse="true|false" - optional="true|false"> - - <key ... /> - - <property ... /> - ... -</join>]]></programlisting> - - <calloutlist> - <callout arearefs="join1"> - <para> - <literal>table</literal>: The name of the joined table. - </para> - </callout> - <callout arearefs="join2"> - <para> - <literal>schema</literal> (optional): Override the schema name specified by - the root <literal>&lt;hibernate-mapping&gt;</literal> element. - </para> - </callout> - <callout arearefs="join3"> - <para> - <literal>catalog</literal> (optional): Override the catalog name specified by - the root <literal>&lt;hibernate-mapping&gt;</literal> element. - </para> - </callout> - <callout arearefs="join4"> - <para> - <literal>fetch</literal> (optional - defaults to <literal>join</literal>): - If set to <literal>join</literal>, the default, Hibernate will use an inner join - to retrieve a <literal>&lt;join&gt;</literal> defined by a class or its superclasses - and an outer join for a <literal>&lt;join&gt;</literal> defined by a subclass. - If set to <literal>select</literal> then Hibernate will use a sequential select for - a <literal>&lt;join&gt;</literal> defined on a subclass, which will be issued only - if a row turns out to represent an instance of the subclass. Inner joins will still - be used to retrieve a <literal>&lt;join&gt;</literal> defined by the class and its - superclasses. - </para> - </callout> - <callout arearefs="join5"> - <para> - <literal>inverse</literal> (optional - defaults to <literal>false</literal>): - If enabled, Hibernate will not try to insert or update the properties defined - by this join. - </para> - </callout> - <callout arearefs="join6"> - <para> - <literal>optional</literal> (optional - defaults to <literal>false</literal>): - If enabled, Hibernate will insert a row only if the properties defined by this - join are non-null and will always use an outer join to retrieve the properties. - </para> - </callout> - </calloutlist> - </programlistingco> - - <para> - For example, the address information for a person can be mapped to a separate - table (while preserving value type semantics for all properties): - </para> - - <programlisting><![CDATA[<class name="Person" - table="PERSON"> - - <id name="id" column="PERSON_ID">...</id> - - <join table="ADDRESS"> - <key column="ADDRESS_ID"/> - <property name="address"/> - <property name="zip"/> - <property name="country"/> - </join> - ...]]></programlisting> - - <para> - This feature is often only useful for legacy data models, we recommend fewer - tables than classes and a fine-grained domain model. However, it is useful - for switching between inheritance mapping strategies in a single hierarchy, as - explained later. - </para> - - </sect2> - - <sect2 id="mapping-declaration-key"> - <title>key</title> - - <para> - We've seen the <literal>&lt;key&gt;</literal> element crop up a few times - now. It appears anywhere the parent mapping element defines a join to - a new table, and defines the foreign key in the joined table, that references - the primary key of the original table. - </para> - - <programlistingco> - <areaspec> - <area id="key1" coords="2 50"/> - <area id="key2" coords="3 50"/> - <area id="key3" coords="4 50"/> - <area id="key4" coords="5 50"/> - <area id="key5" coords="6 50"/> - <area id="key6" coords="7 50"/> - </areaspec> - <programlisting><![CDATA[<key - column="columnname" - on-delete="noaction|cascade" - property-ref="propertyName" - not-null="true|false" - update="true|false" - unique="true|false" -/>]]></programlisting> - - <calloutlist> - <callout arearefs="key1"> - <para> - <literal>column</literal> (optional): The name of the foreign key column. - This may also be specified by nested <literal>&lt;column&gt;</literal> - element(s). - </para> - </callout> - <callout arearefs="key2"> - <para> - <literal>on-delete</literal> (optional, defaults to <literal>noaction</literal>): - Specifies whether the foreign key constraint has database-level cascade delete - enabled. - </para> - </callout> - <callout arearefs="key3"> - <para> - <literal>property-ref</literal> (optional): Specifies that the foreign key refers - to columns that are not the primary key of the orginal table. (Provided for - legacy data.) - </para> - </callout> - <callout arearefs="key4"> - <para> - <literal>not-null</literal> (optional): Specifies that the foreign key columns - are not nullable (this is implied whenever the foreign key is also part of the - primary key). - </para> - </callout> - <callout arearefs="key5"> - <para> - <literal>update</literal> (optional): Specifies that the foreign key should never - be updated (this is implied whenever the foreign key is also part of the primary - key). - </para> - </callout> - <callout arearefs="key6"> - <para> - <literal>unique</literal> (optional): Specifies that the foreign key should have - a unique constraint (this is implied whenever the foreign key is also the primary key). - </para> - </callout> - </calloutlist> - </programlistingco> - - <para> - We recommend that for systems where delete performance is important, all keys should be - defined <literal>on-delete="cascade"</literal>, and Hibernate will use a database-level - <literal>ON CASCADE DELETE</literal> constraint, instead of many individual - <literal>DELETE</literal> statements. Be aware that this feature bypasses Hibernate's - usual optimistic locking strategy for versioned data. - </para> - - <para> - The <literal>not-null</literal> and <literal>update</literal> attributes are useful when - mapping a unidirectional one to many association. If you map a unidirectional one to many - to a non-nullable foreign key, you <emphasis>must</emphasis> declare the key column using - <literal>&lt;key not-null="true"&gt;</literal>. - </para> - - </sect2> - - <sect2 id="mapping-column" revision="4"> - <title>column and formula elements</title> - <para> - Any mapping element which accepts a <literal>column</literal> attribute will alternatively - accept a <literal>&lt;column&gt;</literal> subelement. Likewise, <literal>&lt;formula&gt;</literal> - is an alternative to the <literal>formula</literal> attribute. - </para> - - <programlisting><![CDATA[<column - name="column_name" - length="N" - precision="N" - scale="N" - not-null="true|false" - unique="true|false" - unique-key="multicolumn_unique_key_name" - index="index_name" - sql-type="sql_type_name" - check="SQL expression" - default="SQL expression"/>]]></programlisting> - - <programlisting><![CDATA[<formula>SQL expression</formula>]]></programlisting> - - <para> - <literal>column</literal> and <literal>formula</literal> attributes may even be combined - within the same property or association mapping to express, for example, exotic join - conditions. - </para> - - <programlisting><![CDATA[<many-to-one name="homeAddress" class="Address" - insert="false" update="false"> - <column name="person_id" not-null="true" length="10"/> - <formula>'MAILING'</formula> -</many-to-one>]]></programlisting> - - </sect2> - - <sect2 id="mapping-declaration-import"> - <title>import</title> - - <para> - Suppose your application has two persistent classes with the same name, and you don't want to - specify the fully qualified (package) name in Hibernate queries. Classes may be "imported" - explicitly, rather than relying upon <literal>auto-import="true"</literal>. You may even import - classes and interfaces that are not explicitly mapped. - </para> - - <programlisting><![CDATA[<import class="java.lang.Object" rename="Universe"/>]]></programlisting> - - <programlistingco> - <areaspec> - <area id="import1" coords="2 40"/> - <area id="import2" coords="3 40"/> - </areaspec> - <programlisting><![CDATA[<import - class="ClassName" - rename="ShortName" -/>]]></programlisting> - <calloutlist> - <callout arearefs="import1"> - <para> - <literal>class</literal>: The fully qualified class name of of any Java class. - </para> - </callout> - <callout arearefs="import2"> - <para> - <literal>rename</literal> (optional - defaults to the unqualified class name): - A name that may be used in the query language. - </para> - </callout> - </calloutlist> - </programlistingco> - - </sect2> - - <sect2 id="mapping-types-anymapping" revision="2"> - <title>any</title> - - <para> - There is one further type of property mapping. The <literal>&lt;any&gt;</literal> mapping element - defines a polymorphic association to classes from multiple tables. This type of mapping always - requires more than one column. The first column holds the type of the associated entity. - The remaining columns hold the identifier. It is impossible to specify a foreign key constraint - for this kind of association, so this is most certainly not meant as the usual way of mapping - (polymorphic) associations. You should use this only in very special cases (eg. audit logs, - user session data, etc). - </para> - - <para> - The <literal>meta-type</literal> attribute lets the application specify a custom type that - maps database column values to persistent classes which have identifier properties of the - type specified by <literal>id-type</literal>. You must specify the mapping from values of - the meta-type to class names. - </para> - - <programlisting><![CDATA[<any name="being" id-type="long" meta-type="string"> - <meta-value value="TBL_ANIMAL" class="Animal"/> - <meta-value value="TBL_HUMAN" class="Human"/> - <meta-value value="TBL_ALIEN" class="Alien"/> - <column name="table_name"/> - <column name="id"/> -</any>]]></programlisting> - - <programlistingco> - <areaspec> - <area id="any1" coords="2 50"/> - <area id="any2" coords="3 50"/> - <area id="any3" coords="4 50"/> - <area id="any4" coords="5 50"/> - <area id="any5" coords="6 50"/> - <area id="any6" coords="7 50"/> - </areaspec> - <programlisting><![CDATA[<any - name="propertyName" - id-type="idtypename" - meta-type="metatypename" - cascade="cascade_style" - access="field|property|ClassName" - optimistic-lock="true|false" -> - <meta-value ... /> - <meta-value ... /> - ..... - <column .... /> - <column .... /> - ..... -</any>]]></programlisting> - <calloutlist> - <callout arearefs="any1"> - <para> - <literal>name</literal>: the property name. - </para> - </callout> - <callout arearefs="any2"> - <para> - <literal>id-type</literal>: the identifier type. - </para> - </callout> - <callout arearefs="any3"> - <para> - <literal>meta-type</literal> (optional - defaults to <literal>string</literal>): - Any type that is allowed for a discriminator mapping. - </para> - </callout> - <callout arearefs="any4"> - <para> - <literal>cascade</literal> (optional- defaults to <literal>none</literal>): - the cascade style. - </para> - </callout> - <callout arearefs="any5"> - <para> - <literal>access</literal> (optional - defaults to <literal>property</literal>): The - strategy Hibernate should use for accessing the property value. - </para> - </callout> - <callout arearefs="any6"> - <para> - <literal>optimistic-lock</literal> (optional - defaults to <literal>true</literal>): - Specifies that updates to this property do or do not require acquisition of the - optimistic lock. In other words, define if a version increment should occur if this - property is dirty. - </para> - </callout> - </calloutlist> - </programlistingco> - - </sect2> - - </sect1> - - <sect1 id="mapping-types"> - <title>Hibernate Types</title> - - <sect2 id="mapping-types-entitiesvalues" revision="1"> - <title>Entities and values</title> - - <para> - To understand the behaviour of various Java language-level objects with respect - to the persistence service, we need to classify them into two groups: - </para> - - <para> - An <emphasis>entity</emphasis> exists independently of any other objects holding - references to the entity. Contrast this with the usual Java model where an - unreferenced object is garbage collected. Entities must be explicitly saved and - deleted (except that saves and deletions may be <emphasis>cascaded</emphasis> - from a parent entity to its children). This is different from the ODMG model of - object persistence by reachablity - and corresponds more closely to how - application objects are usually used in large systems. Entities support - circular and shared references. They may also be versioned. - </para> - - <para> - An entity's persistent state consists of references to other entities and - instances of <emphasis>value</emphasis> types. Values are primitives, - collections (not what's inside a collection), components and certain immutable - objects. Unlike entities, values (in particular collections and components) - <emphasis>are</emphasis> persisted and deleted by reachability. Since value - objects (and primitives) are persisted and deleted along with their containing - entity they may not be independently versioned. Values have no independent - identity, so they cannot be shared by two entities or collections. - </para> - - <para> - Up until now, we've been using the term "persistent class" to refer to - entities. We will continue to do that. Strictly speaking, however, not all - user-defined classes with persistent state are entities. A - <emphasis>component</emphasis> is a user defined class with value semantics. - A Java property of type <literal>java.lang.String</literal> also has value - semantics. Given this definition, we can say that all types (classes) provided - by the JDK have value type semantics in Java, while user-defined types may - be mapped with entity or value type semantics. This decision is up to the - application developer. A good hint for an entity class in a domain model are - shared references to a single instance of that class, while composition or - aggregation usually translates to a value type. - </para> - - <para> - We'll revisit both concepts throughout the documentation. - </para> - - <para> - The challenge is to map the Java type system (and the developers' definition of - entities and value types) to the SQL/database type system. The bridge between - both systems is provided by Hibernate: for entities we use - <literal>&lt;class&gt;</literal>, <literal>&lt;subclass&gt;</literal> and so on. - For value types we use <literal>&lt;property&gt;</literal>, - <literal>&lt;component&gt;</literal>, etc, usually with a <literal>type</literal> - attribute. The value of this attribute is the name of a Hibernate - <emphasis>mapping type</emphasis>. Hibernate provides many mappings (for standard - JDK value types) out of the box. You can write your own mapping types and implement your - custom conversion strategies as well, as you'll see later. - </para> - - <para> - All built-in Hibernate types except collections support null semantics. - </para> - - </sect2> - - <sect2 id="mapping-types-basictypes" revision="3"> - <title>Basic value types</title> - - <para> - The built-in <emphasis>basic mapping types</emphasis> may be roughly categorized into - - <variablelist> - <varlistentry> - <term><literal>integer, long, short, float, double, character, byte, - boolean, yes_no, true_false</literal></term> - <listitem> - <para> - Type mappings from Java primitives or wrapper classes to appropriate - (vendor-specific) SQL column types. <literal>boolean, yes_no</literal> - and <literal>true_false</literal> are all alternative encodings for - a Java <literal>boolean</literal> or <literal>java.lang.Boolean</literal>. - </para> - </listitem> - </varlistentry> - <varlistentry> - <term><literal>string</literal></term> - <listitem> - <para> - A type mapping from <literal>java.lang.String</literal> to - <literal>VARCHAR</literal> (or Oracle <literal>VARCHAR2</literal>). - </para> - </listitem> - </varlistentry> - <varlistentry> - <term><literal>date, time, timestamp</literal></term> - <listitem> - <para> - Type mappings from <literal>java.util.Date</literal> and its subclasses - to SQL types <literal>DATE</literal>, <literal>TIME</literal> and - <literal>TIMESTAMP</literal> (or equivalent). - </para> - </listitem> - </varlistentry> - <varlistentry> - <term><literal>calendar, calendar_date</literal></term> - <listitem> - <para> - Type mappings from <literal>java.util.Calendar</literal> to - SQL types <literal>TIMESTAMP</literal> and <literal>DATE</literal> - (or equivalent). - </para> - </listitem> - </varlistentry> - <varlistentry> - <term><literal>big_decimal, big_integer</literal></term> - <listitem> - <para> - Type mappings from <literal>java.math.BigDecimal</literal> and - <literal>java.math.BigInteger</literal> to <literal>NUMERIC</literal> - (or Oracle <literal>NUMBER</literal>). - </para> - </listitem> - </varlistentry> - <varlistentry> - <term><literal>locale, timezone, currency</literal></term> - <listitem> - <para> - Type mappings from <literal>java.util.Locale</literal>, - <literal>java.util.TimeZone</literal> and - <literal>java.util.Currency</literal> - to <literal>VARCHAR</literal> (or Oracle <literal>VARCHAR2</literal>). - Instances of <literal>Locale</literal> and <literal>Currency</literal> are - mapped to their ISO codes. Instances of <literal>TimeZone</literal> are - mapped to their <literal>ID</literal>. - </para> - </listitem> - </varlistentry> - <varlistentry> - <term><literal>class</literal></term> - <listitem> - <para> - A type mapping from <literal>java.lang.Class</literal> to - <literal>VARCHAR</literal> (or Oracle <literal>VARCHAR2</literal>). - A <literal>Class</literal> is mapped to its fully qualified name. - </para> - </listitem> - </varlistentry> - <varlistentry> - <term><literal>binary</literal></term> - <listitem> - <para> - Maps byte arrays to an appropriate SQL binary type. - </para> - </listitem> - </varlistentry> - <varlistentry> - <term><literal>text</literal></term> - <listitem> - <para> - Maps long Java strings to a SQL <literal>CLOB</literal> or - <literal>TEXT</literal> type. - </para> - </listitem> - </varlistentry> - <varlistentry> - <term><literal>serializable</literal></term> - <listitem> - <para> - Maps serializable Java types to an appropriate SQL binary type. You - may also indicate the Hibernate type <literal>serializable</literal> with - the name of a serializable Java class or interface that does not default - to a basic type. - </para> - </listitem> - </varlistentry> - <varlistentry> - <term><literal>clob, blob</literal></term> - <listitem> - <para> - Type mappings for the JDBC classes <literal>java.sql.Clob</literal> and - <literal>java.sql.Blob</literal>. These types may be inconvenient for some - applications, since the blob or clob object may not be reused outside of - a transaction. (Furthermore, driver support is patchy and inconsistent.) - </para> - </listitem> - </varlistentry> - <varlistentry> - <term> - <literal>imm_date, imm_time, imm_timestamp, imm_calendar, imm_calendar_date, - imm_serializable, imm_binary</literal> - </term> - <listitem> - <para> - Type mappings for what are usually considered mutable Java types, where - Hibernate makes certain optimizations appropriate only for immutable - Java types, and the application treats the object as immutable. For - example, you should not call <literal>Date.setTime()</literal> for an - instance mapped as <literal>imm_timestamp</literal>. To change the - value of the property, and have that change made persistent, the - application must assign a new (nonidentical) object to the property. - </para> - </listitem> - </varlistentry> - </variablelist> - - </para> - - <para> - Unique identifiers of entities and collections may be of any basic type except - <literal>binary</literal>, <literal>blob</literal> and <literal>clob</literal>. - (Composite identifiers are also allowed, see below.) - </para> - - <para> - The basic value types have corresponding <literal>Type</literal> constants defined on - <literal>org.hibernate.Hibernate</literal>. For example, <literal>Hibernate.STRING</literal> - represents the <literal>string</literal> type. - </para> - - </sect2> - - <sect2 id="mapping-types-custom" revision="2"> - <title>Custom value types</title> - - <para> - It is relatively easy for developers to create their own value types. For example, - you might want to persist properties of type <literal>java.lang.BigInteger</literal> - to <literal>VARCHAR</literal> columns. Hibernate does not provide a built-in type - for this. But custom types are not limited to mapping a property (or collection element) - to a single table column. So, for example, you might have a Java property - <literal>getName()</literal>/<literal>setName()</literal> of type - <literal>java.lang.String</literal> that is persisted to the columns - <literal>FIRST_NAME</literal>, <literal>INITIAL</literal>, <literal>SURNAME</literal>. - </para> - - <para> - To implement a custom type, implement either <literal>org.hibernate.UserType</literal> - or <literal>org.hibernate.CompositeUserType</literal> and declare properties using the - fully qualified classname of the type. Check out - <literal>org.hibernate.test.DoubleStringType</literal> to see the kind of things that - are possible. - </para> - - <programlisting><![CDATA[<property name="twoStrings" type="org.hibernate.test.DoubleStringType"> - <column name="first_string"/> - <column name="second_string"/> -</property>]]></programlisting> - - <para> - Notice the use of <literal>&lt;column&gt;</literal> tags to map a property to multiple - columns. - </para> - - <para> - The <literal>CompositeUserType</literal>, <literal>EnhancedUserType</literal>, - <literal>UserCollectionType</literal>, and <literal>UserVersionType</literal> - interfaces provide support for more specialized uses. - </para> - - <para> - You may even supply parameters to a <literal>UserType</literal> in the mapping file. To - do this, your <literal>UserType</literal> must implement the - <literal>org.hibernate.usertype.ParameterizedType</literal> interface. To supply parameters - to your custom type, you can use the <literal>&lt;type&gt;</literal> element in your mapping - files. - </para> - - <programlisting><![CDATA[<property name="priority"> - <type name="com.mycompany.usertypes.DefaultValueIntegerType"> - <param name="default">0</param> - </type> -</property>]]></programlisting> - - <para> - The <literal>UserType</literal> can now retrieve the value for the parameter named - <literal>default</literal> from the <literal>Properties</literal> object passed to it. - </para> - - <para> - If you use a certain <literal>UserType</literal> very often, it may be useful to define a - shorter name for it. You can do this using the <literal>&lt;typedef&gt;</literal> element. - Typedefs assign a name to a custom type, and may also contain a list of default - parameter values if the type is parameterized. - </para> - - <programlisting><![CDATA[<typedef class="com.mycompany.usertypes.DefaultValueIntegerType" name="default_zero"> - <param name="default">0</param> -</typedef>]]></programlisting> - - <programlisting><![CDATA[<property name="priority" type="default_zero"/>]]></programlisting> - - <para> - It is also possible to override the parameters supplied in a typedef on a case-by-case basis - by using type parameters on the property mapping. - </para> - - <para> - Even though Hibernate's rich range of built-in types and support for components means you - will very rarely <emphasis>need</emphasis> to use a custom type, it is nevertheless - considered good form to use custom types for (non-entity) classes that occur frequently - in your application. For example, a <literal>MonetaryAmount</literal> class is a good - candidate for a <literal>CompositeUserType</literal>, even though it could easily be mapped - as a component. One motivation for this is abstraction. With a custom type, your mapping - documents would be future-proofed against possible changes in your way of representing - monetary values. - </para> - - </sect2> - - </sect1> - - <sect1 id="mapping-entityname"> - <title>Mapping a class more than once</title> - <para> - It is possible to provide more than one mapping for a particular persistent class. In this - case you must specify an <emphasis>entity name</emphasis> do disambiguate between instances - of the two mapped entities. (By default, the entity name is the same as the class name.) - Hibernate lets you specify the entity name when working with persistent objects, when writing - queries, or when mapping associations to the named entity. - </para> - - <programlisting><![CDATA[<class name="Contract" table="Contracts" - entity-name="CurrentContract"> - ... - <set name="history" inverse="true" - order-by="effectiveEndDate desc"> - <key column="currentContractId"/> - <one-to-many entity-name="HistoricalContract"/> - </set> -</class> - -<class name="Contract" table="ContractHistory" - entity-name="HistoricalContract"> - ... - <many-to-one name="currentContract" - column="currentContractId" - entity-name="CurrentContract"/> -</class>]]></programlisting> - - <para> - Notice how associations are now specified using <literal>entity-name</literal> instead of - <literal>class</literal>. - </para> - - </sect1> - - <sect1 id="mapping-quotedidentifiers"> - <title>SQL quoted identifiers</title> - <para> - You may force Hibernate to quote an identifier in the generated SQL by enclosing the table or - column name in backticks in the mapping document. Hibernate will use the correct quotation - style for the SQL <literal>Dialect</literal> (usually double quotes, but brackets for SQL - Server and backticks for MySQL). - </para> - - <programlisting><![CDATA[<class name="LineItem" table="`Line Item`"> - <id name="id" column="`Item Id`"/><generator class="assigned"/></id> - <property name="itemNumber" column="`Item #`"/> - ... -</class>]]></programlisting> - - </sect1> - - - <sect1 id="mapping-alternatives"> - <title>Metadata alternatives</title> - - <para> - XML isn't for everyone, and so there are some alternative ways to define O/R mapping metadata in Hibernate. - </para> - - <sect2 id="mapping-xdoclet"> - <title>Using XDoclet markup</title> - - <para> - Many Hibernate users prefer to embed mapping information directly in sourcecode using - XDoclet <literal&gt;(a)hibernate.tags&lt;/literal&gt;. We will not cover this approach in this - document, since strictly it is considered part of XDoclet. However, we include the - following example of the <literal>Cat</literal> class with XDoclet mappings. - </para> - - <programlisting><![CDATA[package eg; -import java.util.Set; -import java.util.Date; - -/** - * @hibernate.class - * table="CATS" - */ -public class Cat { - private Long id; // identifier - private Date birthdate; - private Cat mother; - private Set kittens - private Color color; - private char sex; - private float weight; - - /* - * @hibernate.id - * generator-class="native" - * column="CAT_ID" - */ - public Long getId() { - return id; - } - private void setId(Long id) { - this.id=id; - } - - /** - * @hibernate.many-to-one - * column="PARENT_ID" - */ - public Cat getMother() { - return mother; - } - void setMother(Cat mother) { - this.mother = mother; - } - - /** - * @hibernate.property - * column="BIRTH_DATE" - */ - public Date getBirthdate() { - return birthdate; - } - void setBirthdate(Date date) { - birthdate = date; - } - /** - * @hibernate.property - * column="WEIGHT" - */ - public float getWeight() { - return weight; - } - void setWeight(float weight) { - this.weight = weight; - } - - /** - * @hibernate.property - * column="COLOR" - * not-null="true" - */ - public Color getColor() { - return color; - } - void setColor(Color color) { - this.color = color; - } - /** - * @hibernate.set - * inverse="true" - * order-by="BIRTH_DATE" - * @hibernate.collection-key - * column="PARENT_ID" - * @hibernate.collection-one-to-many - */ - public Set getKittens() { - return kittens; - } - void setKittens(Set kittens) { - this.kittens = kittens; - } - // addKitten not needed by Hibernate - public void addKitten(Cat kitten) { - kittens.add(kitten); - } - - /** - * @hibernate.property - * column="SEX" - * not-null="true" - * update="false" - */ - public char getSex() { - return sex; - } - void setSex(char sex) { - this.sex=sex; - } -}]]></programlisting> - - <para> - See the Hibernate web site for more examples of XDoclet and Hibernate. - </para> - - </sect2> - - <sect2 id="mapping-annotations" revision="2"> - <title>Using JDK 5.0 Annotations</title> - - <para> - JDK 5.0 introduced XDoclet-style annotations at the language level, type-safe and - checked at compile time. This mechnism is more powerful than XDoclet annotations and - better supported by tools and IDEs. IntelliJ IDEA, for example, supports auto-completion - and syntax highlighting of JDK 5.0 annotations. The new revision of the EJB specification - (JSR-220) uses JDK 5.0 annotations as the primary metadata mechanism for entity beans. - Hibernate3 implements the <literal>EntityManager</literal> of JSR-220 (the persistence API), - support for mapping metadata is available via the <emphasis>Hibernate Annotations</emphasis> - package, as a separate download. Both EJB3 (JSR-220) and Hibernate3 metadata is supported. - </para> - - <para> - This is an example of a POJO class annotated as an EJB entity bean: - </para> - - <programlisting><![CDATA[@Entity(access = AccessType.FIELD) -public class Customer implements Serializable { - - @Id; - Long id; - - String firstName; - String lastName; - Date birthday; - - @Transient - Integer age; - - @Embedded - private Address homeAddress; - - @OneToMany(cascade=CascadeType.ALL) - @JoinColumn(name="CUSTOMER_ID") - Set<Order> orders; - - // Getter/setter and business methods -}]]></programlisting> - - <para> - Note that support for JDK 5.0 Annotations (and JSR-220) is still work in progress and - not completed. Please refer to the Hibernate Annotations module for more details. - </para> - - </sect2> - </sect1> - - <sect1 id="mapping-generated" revision="1"> - <title>Generated Properties</title> - <para> - Generated properties are properties which have their values generated by the - database. Typically, Hibernate applications needed to <literal>refresh</literal> - objects which contain any properties for which the database was generating values. - Marking properties as generated, however, lets the application delegate this - responsibility to Hibernate. Essentially, whenever Hibernate issues an SQL INSERT - or UPDATE for an entity which has defined generated properties, it immediately - issues a select afterwards to retrieve the generated values. - </para> - <para> - Properties marked as generated must additionally be non-insertable and non-updateable. - Only <link linkend="mapping-declaration-version">versions</link>, - <link linkend="mapping-declaration-timestamp">timestamps</link>, and - <link linkend="mapping-declaration-property">simple properties</link> can be marked as - generated. - </para> - <para> - <literal>never</literal> (the default) - means that the given property value - is not generated within the database. - </para> - <para> - <literal>insert</literal> - states that the given property value is generated on - insert, but is not regenerated on subsequent updates. Things like created-date would - fall into this category. Note that even thought - <link linkend="mapping-declaration-version">version</link> and - <link linkend="mapping-declaration-timestamp">timestamp</link> properties can - be marked as generated, this option is not available there... - </para> - <para> - <literal>always</literal> - states that the property value is generated both - on insert and on update. - </para> - </sect1> - - <sect1 id="mapping-database-object"> - <title>Auxiliary Database Objects</title> - <para> - Allows CREATE and DROP of arbitrary database objects, in conjunction with - Hibernate's schema evolution tools, to provide the ability to fully define - a user schema within the Hibernate mapping files. Although designed specifically - for creating and dropping things like triggers or stored procedures, really any - SQL command that can be run via a <literal>java.sql.Statement.execute()</literal> - method is valid here (ALTERs, INSERTS, etc). There are essentially two modes for - defining auxiliary database objects... - </para> - <para> - The first mode is to explicitly list the CREATE and DROP commands out in the mapping - file: - </para> - <programlisting><![CDATA[<hibernate-mapping> - ... - <database-object> - <create>CREATE TRIGGER my_trigger ...</create> - <drop>DROP TRIGGER my_trigger</drop> - </database-object> -</hibernate-mapping>]]></programlisting> - <para> - The second mode is to supply a custom class which knows how to construct the - CREATE and DROP commands. This custom class must implement the - <literal>org.hibernate.mapping.AuxiliaryDatabaseObject</literal> interface. - </para> - <programlisting><![CDATA[<hibernate-mapping> - ... - <database-object> - <definition class="MyTriggerDefinition"/> - </database-object> -</hibernate-mapping>]]></programlisting> - <para> - Additionally, these database objects can be optionally scoped such that they only - apply when certain dialects are used. - </para> - <programlisting><![CDATA[<hibernate-mapping> - ... - <database-object> - <definition class="MyTriggerDefinition"/> - <dialect-scope name="org.hibernate.dialect.Oracle9Dialect"/> - <dialect-scope name="org.hibernate.dialect.OracleDialect"/> - </database-object> -</hibernate-mapping>]]></programlisting> - </sect1> -</chapter> - Deleted: core/trunk/documentation/envers/src/main/docbook/en-US/content/batch.xml =================================================================== --- core/trunk/documentation/envers/src/main/docbook/en-US/content/batch.xml 2008-11-04 17:31:01 UTC (rev 15499) +++ core/trunk/documentation/envers/src/main/docbook/en-US/content/batch.xml 2008-11-04 17:31:43 UTC (rev 15500) @@ -1,374 +0,0 @@ -<?xml version='1.0' encoding="iso-8859-1"?> -<!-- - ~ Hibernate, Relational Persistence for Idiomatic Java - ~ - ~ Copyright (c) 2008, Red Hat Middleware LLC or third-party contributors as - ~ indicated by the @author tags or express copyright attribution - ~ statements applied by the authors. All third-party contributions are - ~ distributed under license by Red Hat Middleware LLC. - ~ - ~ This copyrighted material is made available to anyone wishing to use, modify, - ~ copy, or redistribute it subject to the terms and conditions of the GNU - ~ Lesser General Public License, as published by the Free Software Foundation. - ~ - ~ This program is distributed in the hope that it will be useful, - ~ but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY - ~ or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License - ~ for more details. - ~ - ~ You should have received a copy of the GNU Lesser General Public License - ~ along with this distribution; if not, write to: - ~ Free Software Foundation, Inc. - ~ 51 Franklin Street, Fifth Floor - ~ Boston, MA 02110-1301 USA - --> - -<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd"> - -<chapter id="batch"> - <title>Batch processing</title> - - <para> - A naive approach to inserting 100 000 rows in the database using Hibernate might - look like this: - </para> - -<programlisting><![CDATA[Session session = sessionFactory.openSession(); -Transaction tx = session.beginTransaction(); -for ( int i=0; i<100000; i++ ) { - Customer customer = new Customer(.....); - session.save(customer); -} -tx.commit(); -session.close();]]></programlisting> - - <para> - This would fall over with an <literal>OutOfMemoryException</literal> somewhere - around the 50 000th row. That's because Hibernate caches all the newly inserted - <literal>Customer</literal> instances in the session-level cache. - </para> - - <para> - In this chapter we'll show you how to avoid this problem. First, however, if you - are doing batch processing, it is absolutely critical that you enable the use of - JDBC batching, if you intend to achieve reasonable performance. Set the JDBC batch - size to a reasonable number (say, 10-50): - </para> - -<programlisting><![CDATA[hibernate.jdbc.batch_size 20]]></programlisting> - - <para id="disablebatching" revision="1"> - Note that Hibernate disables insert batching at the JDBC level transparently if you - use an <literal>identiy</literal> identifier generator. - </para> - - <para> - You also might like to do this kind of work in a process where interaction with - the second-level cache is completely disabled: - </para> - -<programlisting><![CDATA[hibernate.cache.use_second_level_cache false]]></programlisting> - - <para> - However, this is not absolutely necessary, since we can explicitly set the - <literal>CacheMode</literal> to disable interaction with the second-level cache. - </para> - - <sect1 id="batch-inserts"> - <title>Batch inserts</title> - - <para> - When making new objects persistent, you must <literal>flush()</literal> and - then <literal>clear()</literal> the session regularly, to control the size of - the first-level cache. - </para> - -<programlisting><![CDATA[Session session = sessionFactory.openSession(); -Transaction tx = session.beginTransaction(); - -for ( int i=0; i<100000; i++ ) { - Customer customer = new Customer(.....); - session.save(customer); - if ( i % 20 == 0 ) { //20, same as the JDBC batch size - //flush a batch of inserts and release memory: - session.flush(); - session.clear(); - } -} - -tx.commit(); -session.close();]]></programlisting> - - </sect1> - - <sect1 id="batch-update" > - <title>Batch updates</title> - - <para> - For retrieving and updating data the same ideas apply. In addition, you need to - use <literal>scroll()</literal> to take advantage of server-side cursors for - queries that return many rows of data. - </para> - -<programlisting><![CDATA[Session session = sessionFactory.openSession(); -Transaction tx = session.beginTransaction(); - -ScrollableResults customers = session.getNamedQuery("GetCustomers") - .setCacheMode(CacheMode.IGNORE) - .scroll(ScrollMode.FORWARD_ONLY); -int count=0; -while ( customers.next() ) { - Customer customer = (Customer) customers.get(0); - customer.updateStuff(...); - if ( ++count % 20 == 0 ) { - //flush a batch of updates and release memory: - session.flush(); - session.clear(); - } -} - -tx.commit(); -session.close();]]></programlisting> - - </sect1> - - <sect1 id="batch-statelesssession"> - <title>The StatelessSession interface</title> - <para> - Alternatively, Hibernate provides a command-oriented API that may be used for - streaming data to and from the database in the form of detached objects. A - <literal>StatelessSession</literal> has no persistence context associated - with it and does not provide many of the higher-level life cycle semantics. - In particular, a stateless session does not implement a first-level cache nor - interact with any second-level or query cache. It does not implement - transactional write-behind or automatic dirty checking. Operations performed - using a stateless session do not ever cascade to associated instances. Collections - are ignored by a stateless session. Operations performed via a stateless session - bypass Hibernate's event model and interceptors. Stateless sessions are vulnerable - to data aliasing effects, due to the lack of a first-level cache. A stateless - session is a lower-level abstraction, much closer to the underlying JDBC. - </para> - -<programlisting><![CDATA[StatelessSession session = sessionFactory.openStatelessSession(); -Transaction tx = session.beginTransaction(); - -ScrollableResults customers = session.getNamedQuery("GetCustomers") - .scroll(ScrollMode.FORWARD_ONLY); -while ( customers.next() ) { - Customer customer = (Customer) customers.get(0); - customer.updateStuff(...); - session.update(customer); -} - -tx.commit(); -session.close();]]></programlisting> - - <para> - Note that in this code example, the <literal>Customer</literal> instances returned - by the query are immediately detached. They are never associated with any persistence - context. - </para> - - <para> - The <literal>insert(), update()</literal> and <literal>delete()</literal> operations - defined by the <literal>StatelessSession</literal> interface are considered to be - direct database row-level operations, which result in immediate execution of a SQL - <literal>INSERT, UPDATE</literal> or <literal>DELETE</literal> respectively. Thus, - they have very different semantics to the <literal>save(), saveOrUpdate()</literal> - and <literal>delete()</literal> operations defined by the <literal>Session</literal> - interface. - </para> - - </sect1> - - <sect1 id="batch-direct" revision="3"> - <title>DML-style operations</title> - - <para> - As already discussed, automatic and transparent object/relational mapping is concerned - with the management of object state. This implies that the object state is available - in memory, hence manipulating (using the SQL <literal>Data Manipulation Language</literal> - (DML) statements: <literal>INSERT</literal>, <literal>UPDATE</literal>, <literal>DELETE</literal>) - data directly in the database will not affect in-memory state. However, Hibernate provides methods - for bulk SQL-style DML statement execution which are performed through the - Hibernate Query Language (<link linkend="queryhql">HQL</link>). - </para> - - <para> - The pseudo-syntax for <literal>UPDATE</literal> and <literal>DELETE</literal> statements - is: <literal>( UPDATE | DELETE ) FROM? EntityName (WHERE where_conditions)?</literal>. Some - points to note: - </para> - - <itemizedlist spacing="compact"> - <listitem> - <para> - In the from-clause, the FROM keyword is optional - </para> - </listitem> - <listitem> - <para> - There can only be a single entity named in the from-clause; it can optionally be - aliased. If the entity name is aliased, then any property references must - be qualified using that alias; if the entity name is not aliased, then it is - illegal for any property references to be qualified. - </para> - </listitem> - <listitem> - <para> - No <link linkend="queryhql-joins-forms">joins</link> (either implicit or explicit) - can be specified in a bulk HQL query. Sub-queries may be used in the where-clause; - the subqueries, themselves, may contain joins. - </para> - </listitem> - <listitem> - <para> - The where-clause is also optional. - </para> - </listitem> - </itemizedlist> - - <para> - As an example, to execute an HQL <literal>UPDATE</literal>, use the - <literal>Query.executeUpdate()</literal> method (the method is named for - those familiar with JDBC's <literal>PreparedStatement.executeUpdate()</literal>): - </para> - -<programlisting><![CDATA[Session session = sessionFactory.openSession(); -Transaction tx = session.beginTransaction(); - -String hqlUpdate = "update Customer c set c.name = :newName where c.name = :oldName"; -// or String hqlUpdate = "update Customer set name = :newName where name = :oldName"; -int updatedEntities = s.createQuery( hqlUpdate ) - .setString( "newName", newName ) - .setString( "oldName", oldName ) - .executeUpdate(); -tx.commit(); -session.close();]]></programlisting> - - <para> - HQL <literal>UPDATE</literal> statements, by default do not effect the - <link linkend="mapping-declaration-version">version</link> - or the <link linkend="mapping-declaration-timestamp">timestamp</link> property values - for the affected entities; this is in keeping with the EJB3 specification. However, - you can force Hibernate to properly reset the <literal>version</literal> or - <literal>timestamp</literal> property values through the use of a <literal>versioned update</literal>. - This is achieved by adding the <literal>VERSIONED</literal> keyword after the <literal>UPDATE</literal> - keyword. - </para> -<programlisting><![CDATA[Session session = sessionFactory.openSession(); -Transaction tx = session.beginTransaction(); -String hqlVersionedUpdate = "update versioned Customer set name = :newName where name = :oldName"; -int updatedEntities = s.createQuery( hqlUpdate ) - .setString( "newName", newName ) - .setString( "oldName", oldName ) - .executeUpdate(); -tx.commit(); -session.close();]]></programlisting> - - <para> - Note that custom version types (<literal>org.hibernate.usertype.UserVersionType</literal>) - are not allowed in conjunction with a <literal>update versioned</literal> statement. - </para> - - <para> - To execute an HQL <literal>DELETE</literal>, use the same <literal>Query.executeUpdate()</literal> - method: - </para> - -<programlisting><![CDATA[Session session = sessionFactory.openSession(); -Transaction tx = session.beginTransaction(); - -String hqlDelete = "delete Customer c where c.name = :oldName"; -// or String hqlDelete = "delete Customer where name = :oldName"; -int deletedEntities = s.createQuery( hqlDelete ) - .setString( "oldName", oldName ) - .executeUpdate(); -tx.commit(); -session.close();]]></programlisting> - - <para> - The <literal>int</literal> value returned by the <literal>Query.executeUpdate()</literal> - method indicate the number of entities effected by the operation. Consider this may or may not - correlate to the number of rows effected in the database. An HQL bulk operation might result in - multiple actual SQL statements being executed, for joined-subclass, for example. The returned - number indicates the number of actual entities affected by the statement. Going back to the - example of joined-subclass, a delete against one of the subclasses may actually result - in deletes against not just the table to which that subclass is mapped, but also the "root" - table and potentially joined-subclass tables further down the inheritence hierarchy. - </para> - - <para> - The pseudo-syntax for <literal>INSERT</literal> statements is: - <literal>INSERT INTO EntityName properties_list select_statement</literal>. Some - points to note: - </para> - - <itemizedlist spacing="compact"> - <listitem> - <para> - Only the INSERT INTO ... SELECT ... form is supported; not the INSERT INTO ... VALUES ... form. - </para> - <para> - The properties_list is analogous to the <literal>column speficiation</literal> - in the SQL <literal>INSERT</literal> statement. For entities involved in mapped - inheritence, only properties directly defined on that given class-level can be - used in the properties_list. Superclass properties are not allowed; and subclass - properties do not make sense. In other words, <literal>INSERT</literal> - statements are inherently non-polymorphic. - </para> - </listitem> - <listitem> - <para> - select_statement can be any valid HQL select query, with the caveat that the return types - must match the types expected by the insert. Currently, this is checked during query - compilation rather than allowing the check to relegate to the database. Note however - that this might cause problems between Hibernate <literal>Type</literal>s which are - <emphasis>equivalent</emphasis> as opposed to <emphasis>equal</emphasis>. This might cause - issues with mismatches between a property defined as a <literal>org.hibernate.type.DateType</literal> - and a property defined as a <literal>org.hibernate.type.TimestampType</literal>, even though the - database might not make a distinction or might be able to handle the conversion. - </para> - </listitem> - <listitem> - <para> - For the id property, the insert statement gives you two options. You can either - explicitly specify the id property in the properties_list (in which case its value - is taken from the corresponding select expression) or omit it from the properties_list - (in which case a generated value is used). This later option is only available when - using id generators that operate in the database; attempting to use this option with - any "in memory" type generators will cause an exception during parsing. Note that - for the purposes of this discussion, in-database generators are considered to be - <literal>org.hibernate.id.SequenceGenerator</literal> (and its subclasses) and - any implementors of <literal>org.hibernate.id.PostInsertIdentifierGenerator</literal>. - The most notable exception here is <literal>org.hibernate.id.TableHiLoGenerator</literal>, - which cannot be used because it does not expose a selectable way to get its values. - </para> - </listitem> - <listitem> - <para> - For properties mapped as either <literal>version</literal> or <literal>timestamp</literal>, - the insert statement gives you two options. You can either specify the property in the - properties_list (in which case its value is taken from the corresponding select expressions) - or omit it from the properties_list (in which case the <literal>seed value</literal> defined - by the <literal>org.hibernate.type.VersionType</literal> is used). - </para> - </listitem> - </itemizedlist> - - <para> - An example HQL <literal>INSERT</literal> statement execution: - </para> - -<programlisting><![CDATA[Session session = sessionFactory.openSession(); -Transaction tx = session.beginTransaction(); - -String hqlInsert = "insert into DelinquentAccount (id, name) select c.id, c.name from Customer c where ..."; -int createdEntities = s.createQuery( hqlInsert ) - .executeUpdate(); -tx.commit(); -session.close();]]></programlisting> - - </sect1> - -</chapter> Deleted: core/trunk/documentation/envers/src/main/docbook/en-US/content/best_practices.xml =================================================================== --- core/trunk/documentation/envers/src/main/docbook/en-US/content/best_practices.xml 2008-11-04 17:31:01 UTC (rev 15499) +++ core/trunk/documentation/envers/src/main/docbook/en-US/content/best_practices.xml 2008-11-04 17:31:43 UTC (rev 15500) @@ -1,250 +0,0 @@ -<?xml version='1.0' encoding="UTF-8"?> -<!-- - ~ Hibernate, Relational Persistence for Idiomatic Java - ~ - ~ Copyright (c) 2008, Red Hat Middleware LLC or third-party contributors as - ~ indicated by the @author tags or express copyright attribution - ~ statements applied by the authors. All third-party contributions are - ~ distributed under license by Red Hat Middleware LLC. - ~ - ~ This copyrighted material is made available to anyone wishing to use, modify, - ~ copy, or redistribute it subject to the terms and conditions of the GNU - ~ Lesser General Public License, as published by the Free Software Foundation. - ~ - ~ This program is distributed in the hope that it will be useful, - ~ but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY - ~ or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License - ~ for more details. - ~ - ~ You should have received a copy of the GNU Lesser General Public License - ~ along with this distribution; if not, write to: - ~ Free Software Foundation, Inc. - ~ 51 Franklin Street, Fifth Floor - ~ Boston, MA 02110-1301 USA - --> - -<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd"> - -<chapter id="best-practices" revision="3"> - <title>Best Practices</title> - - <variablelist spacing="compact"> - <varlistentry> - <term>Write fine-grained classes and map them using <literal>&lt;component&gt;</literal>.</term> - <listitem> - <para> - Use an <literal>Address</literal> class to encapsulate <literal>street</literal>, - <literal>suburb</literal>, <literal>state</literal>, <literal>postcode</literal>. - This encourages code reuse and simplifies refactoring. - </para> - </listitem> - </varlistentry> - <varlistentry> - <term>Declare identifier properties on persistent classes.</term> - <listitem> - <para> - Hibernate makes identifier properties optional. There are all sorts of reasons why - you should use them. We recommend that identifiers be 'synthetic' (generated, with - no business meaning). - </para> - </listitem> - </varlistentry> - <varlistentry> - <term>Identify natural keys.</term> - <listitem> - <para> - Identify natural keys for all entities, and map them using - <literal>&lt;natural-id&gt;</literal>. Implement <literal>equals()</literal> and - <literal>hashCode()</literal> to compare the properties that make up the natural key. - </para> - </listitem> - </varlistentry> - <varlistentry> - <term>Place each class mapping in its own file.</term> - <listitem> - <para> - Don't use a single monolithic mapping document. Map <literal>com.eg.Foo</literal> in - the file <literal>com/eg/Foo.hbm.xml</literal>. This makes particularly good sense in - a team environment. - </para> - </listitem> - </varlistentry> - <varlistentry> - <term>Load mappings as resources.</term> - <listitem> - <para> - Deploy the mappings along with the classes they map. - </para> - </listitem> - </varlistentry> - <varlistentry> - <term>Consider externalising query strings.</term> - <listitem> - <para> - This is a good practice if your queries call non-ANSI-standard SQL functions. - Externalising the query strings to mapping files will make the application more - portable. - </para> - </listitem> - </varlistentry> - <varlistentry> - <term>Use bind variables.</term> - <listitem> - <para> - As in JDBC, always replace non-constant values by "?". Never use string manipulation to - bind a non-constant value in a query! Even better, consider using named parameters in - queries. - </para> - </listitem> - </varlistentry> - <varlistentry> - <term>Don't manage your own JDBC connections.</term> - <listitem> - <para> - Hibernate lets the application manage JDBC connections. This approach should be considered - a last-resort. If you can't use the built-in connections providers, consider providing your - own implementation of <literal>org.hibernate.connection.ConnectionProvider</literal>. - </para> - </listitem> - </varlistentry> - <varlistentry> - <term>Consider using a custom type.</term> - <listitem> - <para> - Suppose you have a Java type, say from some library, that needs to be persisted but doesn't - provide the accessors needed to map it as a component. You should consider implementing - <literal>org.hibernate.UserType</literal>. This approach frees the application - code from implementing transformations to / from a Hibernate type. - </para> - </listitem> - </varlistentry> - <varlistentry> - <term>Use hand-coded JDBC in bottlenecks.</term> - <listitem> - <para> - In performance-critical areas of the system, some kinds of operations might benefit from - direct JDBC. But please, wait until you <emphasis>know</emphasis> something is a bottleneck. - And don't assume that direct JDBC is necessarily faster. If you need to use direct JDBC, it might - be worth opening a Hibernate <literal>Session</literal> and using that JDBC connection. That - way you can still use the same transaction strategy and underlying connection provider. - </para> - </listitem> - </varlistentry> - <varlistentry> - <term>Understand <literal>Session</literal> flushing.</term> - <listitem> - <para> - From time to time the Session synchronizes its persistent state with the database. Performance will - be affected if this process occurs too often. You may sometimes minimize unnecessary flushing by - disabling automatic flushing or even by changing the order of queries and other operations within a - particular transaction. - </para> - </listitem> - </varlistentry> - <varlistentry> - <term>In a three tiered architecture, consider using detached objects.</term> - <listitem> - <para> - When using a servlet / session bean architecture, you could pass persistent objects loaded in - the session bean to and from the servlet / JSP layer. Use a new session to service each request. - Use <literal>Session.merge()</literal> or <literal>Session.saveOrUpdate()</literal> to - synchronize objects with the database. - </para> - </listitem> - </varlistentry> - <varlistentry> - <term>In a two tiered architecture, consider using long persistence contexts.</term> - <listitem> - <para> - Database Transactions have to be as short as possible for best scalability. However, it is often - neccessary to implement long running <emphasis>application transactions</emphasis>, a single - unit-of-work from the point of view of a user. An application transaction might span several - client request/response cycles. It is common to use detached objects to implement application - transactions. An alternative, extremely appropriate in two tiered architecture, is to maintain - a single open persistence contact (session) for the whole life cycle of the application transaction - and simply disconnect from the JDBC connection at the end of each request and reconnect at the - beginning of the subsequent request. Never share a single session across more than one application - transaction, or you will be working with stale data. - </para> - </listitem> - </varlistentry> - <varlistentry> - <term>Don't treat exceptions as recoverable.</term> - <listitem> - <para> - This is more of a necessary practice than a "best" practice. When an exception occurs, roll back - the <literal>Transaction</literal> and close the <literal>Session</literal>. If you don't, Hibernate - can't guarantee that in-memory state accurately represents persistent state. As a special case of this, - do not use <literal>Session.load()</literal> to determine if an instance with the given identifier - exists on the database; use <literal>Session.get()</literal> or a query instead. - </para> - </listitem> - </varlistentry> - <varlistentry> - <term>Prefer lazy fetching for associations.</term> - <listitem> - <para> - Use eager fetching sparingly. Use proxies and lazy collections for most associations to classes that - are not likely to be completely held in the second-level cache. For associations to cached classes, - where there is an a extremely high probability of a cache hit, explicitly disable eager fetching using - <literal>lazy="false"</literal>. When an join fetching is appropriate to a particular use - case, use a query with a <literal>left join fetch</literal>. - </para> - </listitem> - </varlistentry> - <varlistentry> - <term> - Use the <emphasis>open session in view</emphasis> pattern, or a disciplined - <emphasis>assembly phase</emphasis> to avoid problems with unfetched data. - </term> - <listitem> - <para> - Hibernate frees the developer from writing tedious <emphasis>Data Transfer Objects</emphasis> (DTO). - In a traditional EJB architecture, DTOs serve dual purposes: first, they work around the problem - that entity beans are not serializable; second, they implicitly define an assembly phase where - all data to be used by the view is fetched and marshalled into the DTOs before returning control - to the presentation tier. Hibernate eliminates the first purpose. However, you will still need - an assembly phase (think of your business methods as having a strict contract with the presentation - tier about what data is available in the detached objects) unless you are prepared to hold the - persistence context (the session) open across the view rendering process. This is not a limitation - of Hibernate! It is a fundamental requirement of safe transactional data access. - </para> - </listitem> - </varlistentry> - <varlistentry> - <term>Consider abstracting your business logic from Hibernate.</term> - <listitem> - <para> - Hide (Hibernate) data-access code behind an interface. Combine the <emphasis>DAO</emphasis> and - <emphasis>Thread Local Session</emphasis> patterns. You can even have some classes persisted by - handcoded JDBC, associated to Hibernate via a <literal>UserType</literal>. (This advice is - intended for "sufficiently large" applications; it is not appropriate for an application with - five tables!) - </para> - </listitem> - </varlistentry> - <varlistentry> - <term>Don't use exotic association mappings.</term> - <listitem> - <para> - Good usecases for a real many-to-many associations are rare. Most of the time you need - additional information stored in the "link table". In this case, it is much better to - use two one-to-many associations to an intermediate link class. In fact, we think that - most associations are one-to-many and many-to-one, you should be careful when using any - other association style and ask yourself if it is really neccessary. - </para> - </listitem> - </varlistentry> - <varlistentry> - <term>Prefer bidirectional associations.</term> - <listitem> - <para> - Unidirectional associations are more difficult to query. In a large application, almost - all associations must be navigable in both directions in queries. - </para> - </listitem> - </varlistentry> - </variablelist> - -</chapter> - Deleted: core/trunk/documentation/envers/src/main/docbook/en-US/content/collection_mapping.xml =================================================================== --- core/trunk/documentation/envers/src/main/docbook/en-US/content/collection_mapping.xml 2008-11-04 17:31:01 UTC (rev 15499) +++ core/trunk/documentation/envers/src/main/docbook/en-US/content/collection_mapping.xml 2008-11-04 17:31:43 UTC (rev 15500) @@ -1,1260 +0,0 @@ -<?xml version='1.0' encoding="UTF-8"?> -<!-- - ~ Hibernate, Relational Persistence for Idiomatic Java - ~ - ~ Copyright (c) 2008, Red Hat Middleware LLC or third-party contributors as - ~ indicated by the @author tags or express copyright attribution - ~ statements applied by the authors. All third-party contributions are - ~ distributed under license by Red Hat Middleware LLC. - ~ - ~ This copyrighted material is made available to anyone wishing to use, modify, - ~ copy, or redistribute it subject to the terms and conditions of the GNU - ~ Lesser General Public License, as published by the Free Software Foundation. - ~ - ~ This program is distributed in the hope that it will be useful, - ~ but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY - ~ or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License - ~ for more details. - ~ - ~ You should have received a copy of the GNU Lesser General Public License - ~ along with this distribution; if not, write to: - ~ Free Software Foundation, Inc. - ~ 51 Franklin Street, Fifth Floor - ~ Boston, MA 02110-1301 USA - --> - -<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd"> - -<chapter id="collections"> - <title>Collection Mapping</title> - - <sect1 id="collections-persistent" revision="3"> - <title>Persistent collections</title> - - <para> - Hibernate requires that persistent collection-valued fields be declared - as an interface type, for example: - </para> - - <programlisting><![CDATA[public class Product { - private String serialNumber; - private Set parts = new HashSet(); - - public Set getParts() { return parts; } - void setParts(Set parts) { this.parts = parts; } - public String getSerialNumber() { return serialNumber; } - void setSerialNumber(String sn) { serialNumber = sn; } -}]]></programlisting> - - <para> - The actual interface might be <literal>java.util.Set</literal>, - <literal>java.util.Collection</literal>, <literal>java.util.List</literal>, - <literal>java.util.Map</literal>, <literal>java.util.SortedSet</literal>, - <literal>java.util.SortedMap</literal> or ... anything you like! (Where - "anything you like" means you will have to write an implementation of - <literal>org.hibernate.usertype.UserCollectionType</literal>.) - </para> - - <para> - Notice how we initialized the instance variable with an instance of - <literal>HashSet</literal>. This is the best way to initialize collection - valued properties of newly instantiated (non-persistent) instances. When - you make the instance persistent - by calling <literal>persist()</literal>, - for example - Hibernate will actually replace the <literal>HashSet</literal> - with an instance of Hibernate's own implementation of <literal>Set</literal>. - Watch out for errors like this: - </para> - - <programlisting><![CDATA[Cat cat = new DomesticCat(); -Cat kitten = new DomesticCat(); -.... -Set kittens = new HashSet(); -kittens.add(kitten); -cat.setKittens(kittens); -session.persist(cat); -kittens = cat.getKittens(); // Okay, kittens collection is a Set -(HashSet) cat.getKittens(); // Error!]]></programlisting> - - <para> - The persistent collections injected by Hibernate behave like - <literal>HashMap</literal>, <literal>HashSet</literal>, - <literal>TreeMap</literal>, <literal>TreeSet</literal> or - <literal>ArrayList</literal>, depending upon the interface type. - </para> - - <para> - Collections instances have the usual behavior of value types. They are - automatically persisted when referenced by a persistent object and - automatically deleted when unreferenced. If a collection is passed from one - persistent object to another, its elements might be moved from one table to - another. Two entities may not share a reference to the same collection - instance. Due to the underlying relational model, collection-valued properties - do not support null value semantics; Hibernate does not distinguish between - a null collection reference and an empty collection. - </para> - - <para> - You shouldn't have to worry much about any of this. Use persistent collections - the same way you use ordinary Java collections. Just make sure you understand - the semantics of bidirectional associations (discussed later). - </para> - - </sect1> - - <sect1 id="collections-mapping" revision="4"> - <title>Collection mappings</title> - - <tip> - <para> - There are quite a range of mappings that can be generated for collections, covering - many common relational models. We suggest you experiment with the schema generation tool - to get a feeling for how various mapping declarations translate to database tables. - </para> - </tip> - - <para> - The Hibernate mapping element used for mapping a collection depends upon - the type of the interface. For example, a <literal>&lt;set&gt;</literal> - element is used for mapping properties of type <literal>Set</literal>. - </para> - - <programlisting><![CDATA[<class name="Product"> - <id name="serialNumber" column="productSerialNumber"/> - <set name="parts"> - <key column="productSerialNumber" not-null="true"/> - <one-to-many class="Part"/> - </set> -</class>]]></programlisting> - - <para> - Apart from <literal>&lt;set&gt;</literal>, there is also - <literal>&lt;list&gt;</literal>, <literal>&lt;map&gt;</literal>, - <literal>&lt;bag&gt;</literal>, <literal>&lt;array&gt;</literal> and - <literal>&lt;primitive-array&gt;</literal> mapping elements. The - <literal>&lt;map&gt;</literal> element is representative: - </para> - - <programlistingco> - <areaspec> - <area id="mappingcollection1" coords="2 65"/> - <area id="mappingcollection2" coords="3 65"/> - <area id="mappingcollection3" coords="4 65"/> - <area id="mappingcollection4" coords="5 65"/> - <area id="mappingcollection5" coords="6 65"/> - <area id="mappingcollection6" coords="7 65"/> - <area id="mappingcollection7" coords="8 65"/> - <area id="mappingcollection8" coords="9 65"/> - <area id="mappingcollection9" coords="10 65"/> - <area id="mappingcollection10" coords="11 65"/> - <area id="mappingcollection11" coords="12 65"/> - <area id="mappingcollection12" coords="13 65"/> - <area id="mappingcollection13" coords="14 65"/> - <area id="mappingcollection14" coords="15 65"/> - </areaspec> - <programlisting><![CDATA[<map - name="propertyName" - table="table_name" - schema="schema_name" - lazy="true|extra|false" - inverse="true|false" - cascade="all|none|save-update|delete|all-delete-orphan|delete-orphan" - sort="unsorted|natural|comparatorClass" - order-by="column_name asc|desc" - where="arbitrary sql where condition" - fetch="join|select|subselect" - batch-size="N" - access="field|property|ClassName" - optimistic-lock="true|false" - mutable="true|false" - node="element-name|." - embed-xml="true|false" -> - - <key .... /> - <map-key .... /> - <element .... /> -</map>]]></programlisting> - <calloutlist> - <callout arearefs="mappingcollection1"> - <para> - <literal>name</literal> the collection property name - </para> - </callout> - <callout arearefs="mappingcollection2"> - <para> - <literal>table</literal> (optional - defaults to property name) the - name of the collection table (not used for one-to-many associations) - </para> - </callout> - <callout arearefs="mappingcollection3"> - <para> - <literal>schema</literal> (optional) the name of a table schema to - override the schema declared on the root element - </para> - </callout> - <callout arearefs="mappingcollection4"> - <para> - <literal>lazy</literal> (optional - defaults to <literal>true</literal>) - may be used to disable lazy fetching and specify that the association is - always eagerly fetched, or to enable "extra-lazy" fetching where most - operations do not initialize the collection (suitable for very large - collections) - </para> - </callout> - <callout arearefs="mappingcollection5"> - <para> - <literal>inverse</literal> (optional - defaults to <literal>false</literal>) - mark this collection as the "inverse" end of a bidirectional association - </para> - </callout> - <callout arearefs="mappingcollection6"> - <para> - <literal>cascade</literal> (optional - defaults to <literal>none</literal>) - enable operations to cascade to child entities - </para> - </callout> - <callout arearefs="mappingcollection7"> - <para> - <literal>sort</literal> (optional) specify a sorted collection with - <literal>natural</literal> sort order, or a given comparator class - </para> - </callout> - <callout arearefs="mappingcollection8"> - <para> - <literal>order-by</literal> (optional, JDK1.4 only) specify a table column (or columns) - that define the iteration order of the <literal>Map</literal>, <literal>Set</literal> - or bag, together with an optional <literal>asc</literal> or <literal>desc</literal> - </para> - </callout> - <callout arearefs="mappingcollection9"> - <para> - <literal>where</literal> (optional) specify an arbitrary SQL <literal>WHERE</literal> - condition to be used when retrieving or removing the collection (useful if the - collection should contain only a subset of the available data) - </para> - </callout> - <callout arearefs="mappingcollection10"> - <para> - <literal>fetch</literal> (optional, defaults to <literal>select</literal>) Choose - between outer-join fetching, fetching by sequential select, and fetching by sequential - subselect. - </para> - </callout> - <callout arearefs="mappingcollection11"> - <para> - <literal>batch-size</literal> (optional, defaults to <literal>1</literal>) specify a - "batch size" for lazily fetching instances of this collection. - </para> - </callout> - <callout arearefs="mappingcollection12"> - <para> - <literal>access</literal> (optional - defaults to <literal>property</literal>): The - strategy Hibernate should use for accessing the collection property value. - </para> - </callout> - <callout arearefs="mappingcollection13"> - <para> - <literal>optimistic-lock</literal> (optional - defaults to <literal>true</literal>): - Species that changes to the state of the collection results in increment of the - owning entity's version. (For one to many associations, it is often reasonable to - disable this setting.) - </para> - </callout> - <callout arearefs="mappingcollection14"> - <para> - <literal>mutable</literal> (optional - defaults to <literal>true</literal>): - A value of <literal>false</literal> specifies that the elements of the - collection never change (a minor performance optimization in some cases). - </para> - </callout> - </calloutlist> - </programlistingco> - - <sect2 id="collections-foreignkeys" > - <title>Collection foreign keys</title> - - <para> - Collection instances are distinguished in the database by the foreign key of - the entity that owns the collection. This foreign key is referred to as the - <emphasis>collection key column</emphasis> (or columns) of the collection - table. The collection key column is mapped by the <literal>&lt;key&gt;</literal> - element. - </para> - - <para> - There may be a nullability constraint on the foreign key column. For most - collections, this is implied. For unidirectional one to many associations, - the foreign key column is nullable by default, so you might need to specify - <literal>not-null="true"</literal>. - </para> - - <programlisting><![CDATA[<key column="productSerialNumber" not-null="true"/>]]></programlisting> - - <para> - The foreign key constraint may use <literal>ON DELETE CASCADE</literal>. - </para> - - <programlisting><![CDATA[<key column="productSerialNumber" on-delete="cascade"/>]]></programlisting> - - <para> - See the previous chapter for a full definition of the <literal>&lt;key&gt;</literal> - element. - </para> - - </sect2> - - <sect2 id="collections-elements" > - <title>Collection elements</title> - - <para> - Collections may contain almost any other Hibernate type, including all basic types, - custom types, components, and of course, references to other entities. This is an - important distinction: an object in a collection might be handled with "value" - semantics (its life cycle fully depends on the collection owner) or it might be a - reference to another entity, with its own life cycle. In the latter case, only the - "link" between the two objects is considered to be state held by the collection. - </para> - - <para> - The contained type is referred to as the <emphasis>collection element type</emphasis>. - Collection elements are mapped by <literal>&lt;element&gt;</literal> or - <literal>&lt;composite-element&gt;</literal>, or in the case of entity references, - with <literal>&lt;one-to-many&gt;</literal> or <literal>&lt;many-to-many&gt;</literal>. - The first two map elements with value semantics, the next two are used to map entity - associations. - </para> - - </sect2> - - <sect2 id="collections-indexed"> - <title>Indexed collections</title> - - <para> - All collection mappings, except those with set and bag semantics, need an - <emphasis>index column</emphasis> in the collection table - a column that maps to an - array index, or <literal>List</literal> index, or <literal>Map</literal> key. The - index of a <literal>Map</literal> may be of any basic type, mapped with - <literal>&lt;map-key&gt;</literal>, it may be an entity reference mapped with - <literal>&lt;map-key-many-to-many&gt;</literal>, or it may be a composite type, - mapped with <literal>&lt;composite-map-key&gt;</literal>. The index of an array or - list is always of type <literal>integer</literal> and is mapped using the - <literal>&lt;list-index&gt;</literal> element. The mapped column contains - sequential integers (numbered from zero, by default). - </para> - - <programlistingco> - <areaspec> - <area id="index1" coords="2 45"/> - <area id="index2" coords="3 45"/> - </areaspec> - <programlisting><![CDATA[<list-index - column="column_name" - base="0|1|..."/>]]></programlisting> - <calloutlist> - <callout arearefs="index1"> - <para> - <literal>column_name</literal> (required): The name of the column holding the - collection index values. - </para> - </callout> - <callout arearefs="index1"> - <para> - <literal>base</literal> (optional, defaults to <literal>0</literal>): The value - of the index column that corresponds to the first element of the list or array. - </para> - </callout> - </calloutlist> - </programlistingco> - - <programlistingco> - <areaspec> - <area id="mapkey1" coords="2 45"/> - <area id="mapkey2" coords="3 45"/> - <area id="mapkey3" coords="4 45"/> - </areaspec> - <programlisting><![CDATA[<map-key - column="column_name" - formula="any SQL expression" - type="type_name" - node="@attribute-name" - length="N"/>]]></programlisting> - <calloutlist> - <callout arearefs="mapkey1"> - <para> - <literal>column</literal> (optional): The name of the column holding the - collection index values. - </para> - </callout> - <callout arearefs="mapkey2"> - <para> - <literal>formula</literal> (optional): A SQL formula used to evaluate the - key of the map. - </para> - </callout> - <callout arearefs="mapkey3"> - <para> - <literal>type</literal> (reguired): The type of the map keys. - </para> - </callout> - </calloutlist> - </programlistingco> - - <programlistingco> - <areaspec> - <area id="indexmanytomany1" coords="2 45"/> - <area id="indexmanytomany2" coords="3 45"/> - <area id="indexmanytomany3" coords="3 45"/> - </areaspec> - <programlisting><![CDATA[<map-key-many-to-many - column="column_name" - formula="any SQL expression" - class="ClassName" -/>]]></programlisting> - <calloutlist> - <callout arearefs="indexmanytomany1"> - <para> - <literal>column</literal> (optional): The name of the foreign key - column for the collection index values. - </para> - </callout> - <callout arearefs="indexmanytomany2"> - <para> - <literal>formula</literal> (optional): A SQL formula used to evaluate the - foreign key of the map key. - </para> - </callout> - <callout arearefs="indexmanytomany3"> - <para> - <literal>class</literal> (required): The entity class used as the map key. - </para> - </callout> - </calloutlist> - </programlistingco> - - - <para> - If your table doesn't have an index column, and you still wish to use <literal>List</literal> - as the property type, you should map the property as a Hibernate <emphasis>&lt;bag&gt;</emphasis>. - A bag does not retain its order when it is retrieved from the database, but it may be - optionally sorted or ordered. - </para> - - </sect2> - - <sect2 id="collections-ofvalues" revision="2"> - <title>Collections of values and many-to-many associations</title> - - <para> - Any collection of values or many-to-many association requires a dedicated - <emphasis>collection table</emphasis> with a foreign key column or columns, - <emphasis>collection element column</emphasis> or columns and possibly - an index column or columns. - </para> - - <para> - For a collection of values, we use the <literal>&lt;element&gt;</literal> tag. - </para> - - <programlistingco> - <areaspec> - <area id="element1b" coords="2 50"/> - <area id="element2b" coords="3 50"/> - <area id="element3b" coords="4 50"/> - </areaspec> - <programlisting><![CDATA[<element - column="column_name" - formula="any SQL expression" - type="typename" - length="L" - precision="P" - scale="S" - not-null="true|false" - unique="true|false" - node="element-name" -/>]]></programlisting> - <calloutlist> - <callout arearefs="element1b"> - <para> - <literal>column</literal> (optional): The name of the column holding the - collection element values. - </para> - </callout> - <callout arearefs="element2b"> - <para> - <literal>formula</literal> (optional): An SQL formula used to evaluate the - element. - </para> - </callout> - <callout arearefs="element3b"> - <para> - <literal>type</literal> (required): The type of the collection element. - </para> - </callout> - </calloutlist> - </programlistingco> - - <para> - A <emphasis>many-to-many association</emphasis> is specified using the - <literal>&lt;many-to-many&gt;</literal> element. - </para> - - <programlistingco> - <areaspec> - <area id="manytomany1" coords="2 60"/> - <area id="manytomany2" coords="3 60"/> - <area id="manytomany3" coords="4 60"/> - <area id="manytomany4" coords="5 60"/> - <area id="manytomany5" coords="6 60"/> - <area id="manytomany6" coords="7 60"/> - <area id="manytomany7" coords="8 60"/> - <area id="manytomany8" coords="9 60"/> - </areaspec> - <programlisting><![CDATA[<many-to-many - column="column_name" - formula="any SQL expression" - class="ClassName" - fetch="select|join" - unique="true|false" - not-found="ignore|exception" - entity-name="EntityName" - property-ref="propertyNameFromAssociatedClass" - node="element-name" - embed-xml="true|false" - />]]></programlisting> - <calloutlist> - <callout arearefs="manytomany1"> - <para> - <literal>column</literal> (optional): The name of the element foreign key column. - </para> - </callout> - <callout arearefs="manytomany2"> - <para> - <literal>formula</literal> (optional): An SQL formula used to evaluate the element - foreign key value. - </para> - </callout> - <callout arearefs="manytomany3"> - <para> - <literal>class</literal> (required): The name of the associated class. - </para> - </callout> - <callout arearefs="manytomany4"> - <para> - <literal>fetch</literal> (optional - defaults to <literal>join</literal>): - enables outer-join or sequential select fetching for this association. This - is a special case; for full eager fetching (in a single <literal>SELECT</literal>) - of an entity and its many-to-many relationships to other entities, you would - enable <literal>join</literal> fetching not only of the collection itself, - but also with this attribute on the <literal>&lt;many-to-many&gt;</literal> - nested element. - </para> - </callout> - <callout arearefs="manytomany5"> - <para> - <literal>unique</literal> (optional): Enable the DDL generation of a unique - constraint for the foreign-key column. This makes the association multiplicity - effectively one to many. - </para> - </callout> - <callout arearefs="manytomany6"> - <para> - <literal>not-found</literal> (optional - defaults to <literal>exception</literal>): - Specifies how foreign keys that reference missing rows will be handled: - <literal>ignore</literal> will treat a missing row as a null association. - </para> - </callout> - <callout arearefs="manytomany7"> - <para> - <literal>entity-name</literal> (optional): The entity name of the associated class, - as an alternative to <literal>class</literal>. - </para> - </callout> - <callout arearefs="manytomany8"> - <para> - <literal>property-ref</literal>: (optional) The name of a property of the associated - class that is joined to this foreign key. If not specified, the primary key of - the associated class is used. - </para> - </callout> - </calloutlist> - </programlistingco> - - <para> - Some examples, first, a set of strings: - </para> - - <programlisting><![CDATA[<set name="names" table="person_names"> - <key column="person_id"/> - <element column="person_name" type="string"/> -</set>]]></programlisting> - - <para> - A bag containing integers (with an iteration order determined by the - <literal>order-by</literal> attribute): - </para> - - <programlisting><![CDATA[<bag name="sizes" - table="item_sizes" - order-by="size asc"> - <key column="item_id"/> - <element column="size" type="integer"/> -</bag>]]></programlisting> - - <para> - An array of entities - in this case, a many to many association: - </para> - - <programlisting><![CDATA[<array name="addresses" - table="PersonAddress" - cascade="persist"> - <key column="personId"/> - <list-index column="sortOrder"/> - <many-to-many column="addressId" class="Address"/> -</array>]]></programlisting> - - <para> - A map from string indices to dates: - </para> - - <programlisting><![CDATA[<map name="holidays" - table="holidays" - schema="dbo" - order-by="hol_name asc"> - <key column="id"/> - <map-key column="hol_name" type="string"/> - <element column="hol_date" type="date"/> -</map>]]></programlisting> - - <para> - A list of components (discussed in the next chapter): - </para> - - <programlisting><![CDATA[<list name="carComponents" - table="CarComponents"> - <key column="carId"/> - <list-index column="sortOrder"/> - <composite-element class="CarComponent"> - <property name="price"/> - <property name="type"/> - <property name="serialNumber" column="serialNum"/> - </composite-element> -</list>]]></programlisting> - - </sect2> - - <sect2 id="collections-onetomany"> - <title>One-to-many associations</title> - - <para> - A <emphasis>one to many association</emphasis> links the tables of two classes - via a foreign key, with no intervening collection table. This mapping loses - certain semantics of normal Java collections: - </para> - - <itemizedlist spacing="compact"> - <listitem> - <para> - An instance of the contained entity class may not belong to more than - one instance of the collection - </para> - </listitem> - <listitem> - <para> - An instance of the contained entity class may not appear at more than - one value of the collection index - </para> - </listitem> - </itemizedlist> - - <para> - An association from <literal>Product</literal> to <literal>Part</literal> requires - existence of a foreign key column and possibly an index column to the <literal>Part</literal> - table. A <literal>&lt;one-to-many&gt;</literal> tag indicates that this is a one to many - association. - </para> - - <programlistingco> - <areaspec> - <area id="onetomany1" coords="2 60"/> - <area id="onetomany2" coords="3 60"/> - <area id="onetomany3" coords="4 60"/> - </areaspec> - <programlisting><![CDATA[<one-to-many - class="ClassName" - not-found="ignore|exception" - entity-name="EntityName" - node="element-name" - embed-xml="true|false" - />]]></programlisting> - <calloutlist> - <callout arearefs="onetomany1"> - <para> - <literal>class</literal> (required): The name of the associated class. - </para> - </callout> - <callout arearefs="onetomany2"> - <para> - <literal>not-found</literal> (optional - defaults to <literal>exception</literal>): - Specifies how cached identifiers that reference missing rows will be handled: - <literal>ignore</literal> will treat a missing row as a null association. - </para> - </callout> - <callout arearefs="onetomany3"> - <para> - <literal>entity-name</literal> (optional): The entity name of the associated class, - as an alternative to <literal>class</literal>. - </para> - </callout> - </calloutlist> - </programlistingco> - - <para> - Notice that the <literal>&lt;one-to-many&gt;</literal> element does not need to - declare any columns. Nor is it necessary to specify the <literal>table</literal> - name anywhere. - </para> - - <para> - <emphasis>Very important note:</emphasis> If the foreign key column of a - <literal>&lt;one-to-many&gt;</literal> association is declared <literal>NOT NULL</literal>, - you must declare the <literal>&lt;key&gt;</literal> mapping - <literal>not-null="true"</literal> or <emphasis>use a bidirectional association</emphasis> - with the collection mapping marked <literal>inverse="true"</literal>. See the discussion - of bidirectional associations later in this chapter. - </para> - - <para> - This example shows a map of <literal>Part</literal> entities by name (where - <literal>partName</literal> is a persistent property of <literal>Part</literal>). - Notice the use of a formula-based index. - </para> - - <programlisting><![CDATA[<map name="parts" - cascade="all"> - <key column="productId" not-null="true"/> - <map-key formula="partName"/> - <one-to-many class="Part"/> -</map>]]></programlisting> - </sect2> - - </sect1> - - <sect1 id="collections-advancedmappings"> - <title>Advanced collection mappings</title> - - <sect2 id="collections-sorted" revision="2"> - <title>Sorted collections</title> - - <para> - Hibernate supports collections implementing <literal>java.util.SortedMap</literal> and - <literal>java.util.SortedSet</literal>. You must specify a comparator in the mapping file: - </para> - - <programlisting><![CDATA[<set name="aliases" - table="person_aliases" - sort="natural"> - <key column="person"/> - <element column="name" type="string"/> -</set> - -<map name="holidays" sort="my.custom.HolidayComparator"> - <key column="year_id"/> - <map-key column="hol_name" type="string"/> - <element column="hol_date" type="date"/> -</map>]]></programlisting> - - <para> - Allowed values of the <literal>sort</literal> attribute are <literal>unsorted</literal>, - <literal>natural</literal> and the name of a class implementing - <literal>java.util.Comparator</literal>. - </para> - - <para> - Sorted collections actually behave like <literal>java.util.TreeSet</literal> or - <literal>java.util.TreeMap</literal>. - </para> - - <para> - If you want the database itself to order the collection elements use the - <literal>order-by</literal> attribute of <literal>set</literal>, <literal>bag</literal> - or <literal>map</literal> mappings. This solution is only available under - JDK 1.4 or higher (it is implemented using <literal>LinkedHashSet</literal> or - <literal>LinkedHashMap</literal>). This performs the ordering in the SQL query, - not in memory. - </para> - - <programlisting><![CDATA[<set name="aliases" table="person_aliases" order-by="lower(name) asc"> - <key column="person"/> - <element column="name" type="string"/> -</set> - -<map name="holidays" order-by="hol_date, hol_name"> - <key column="year_id"/> - <map-key column="hol_name" type="string"/> - <element column="hol_date type="date"/> -</map>]]></programlisting> - - <para> - Note that the value of the <literal>order-by</literal> attribute is an SQL ordering, not - a HQL ordering! - </para> - - <para> - Associations may even be sorted by some arbitrary criteria at runtime using a collection - <literal>filter()</literal>. - </para> - - <programlisting><![CDATA[sortedUsers = s.createFilter( group.getUsers(), "order by this.name" ).list();]]></programlisting> - - </sect2> - - <sect2 id="collections-bidirectional" revision="1"> - <title>Bidirectional associations</title> - - <para> - A <emphasis>bidirectional association</emphasis> allows navigation from both - "ends" of the association. Two kinds of bidirectional association are - supported: - - <variablelist> - <varlistentry> - <term>one-to-many</term> - <listitem> - <para> - set or bag valued at one end, single-valued at the other - </para> - </listitem> - </varlistentry> - <varlistentry> - <term>many-to-many</term> - <listitem> - <para> - set or bag valued at both ends - </para> - </listitem> - </varlistentry> - </variablelist> - - </para> - - <para> - You may specify a bidirectional many-to-many association simply by mapping two - many-to-many associations to the same database table and declaring one end as - <emphasis>inverse</emphasis> (which one is your choice, but it can not be an - indexed collection). - </para> - - <para> - Here's an example of a bidirectional many-to-many association; each category can - have many items and each item can be in many categories: - </para> - - <programlisting><![CDATA[<class name="Category"> - <id name="id" column="CATEGORY_ID"/> - ... - <bag name="items" table="CATEGORY_ITEM"> - <key column="CATEGORY_ID"/> - <many-to-many class="Item" column="ITEM_ID"/> - </bag> -</class> - -<class name="Item"> - <id name="id" column="ITEM_ID"/> - ... - - <!-- inverse end --> - <bag name="categories" table="CATEGORY_ITEM" inverse="true"> - <key column="ITEM_ID"/> - <many-to-many class="Category" column="CATEGORY_ID"/> - </bag> -</class>]]></programlisting> - - <para> - Changes made only to the inverse end of the association are <emphasis>not</emphasis> - persisted. This means that Hibernate has two representations in memory for every - bidirectional association, one link from A to B and another link from B to A. This - is easier to understand if you think about the Java object model and how we create - a many-to-many relationship in Java: - </para> - - <programlisting><![CDATA[ -category.getItems().add(item); // The category now "knows" about the relationship -item.getCategories().add(category); // The item now "knows" about the relationship - -session.persist(item); // The relationship won't be saved! -session.persist(category); // The relationship will be saved]]></programlisting> - - <para> - The non-inverse side is used to save the in-memory representation to the database. - </para> - - <para> - You may define a bidirectional one-to-many association by mapping a one-to-many association - to the same table column(s) as a many-to-one association and declaring the many-valued - end <literal>inverse="true"</literal>. - </para> - - <programlisting><![CDATA[<class name="Parent"> - <id name="id" column="parent_id"/> - .... - <set name="children" inverse="true"> - <key column="parent_id"/> - <one-to-many class="Child"/> - </set> -</class> - -<class name="Child"> - <id name="id" column="child_id"/> - .... - <many-to-one name="parent" - class="Parent" - column="parent_id" - not-null="true"/> -</class>]]></programlisting> - - <para> - Mapping one end of an association with <literal>inverse="true"</literal> doesn't - affect the operation of cascades, these are orthogonal concepts! - </para> - - </sect2> - - <sect2 id="collections-indexedbidirectional"> - <title>Bidirectional associations with indexed collections</title> - <para> - A bidirectional association where one end is represented as a <literal>&lt;list&gt;</literal> - or <literal>&lt;map&gt;</literal> requires special consideration. If there is a property of - the child class which maps to the index column, no problem, we can continue using - <literal>inverse="true"</literal> on the collection mapping: - </para> - - <programlisting><![CDATA[<class name="Parent"> - <id name="id" column="parent_id"/> - .... - <map name="children" inverse="true"> - <key column="parent_id"/> - <map-key column="name" - type="string"/> - <one-to-many class="Child"/> - </map> -</class> - -<class name="Child"> - <id name="id" column="child_id"/> - .... - <property name="name" - not-null="true"/> - <many-to-one name="parent" - class="Parent" - column="parent_id" - not-null="true"/> -</class>]]></programlisting> - - <para> - But, if there is no such property on the child class, we can't think of the association as - truly bidirectional (there is information available at one end of the association that is - not available at the other end). In this case, we can't map the collection - <literal>inverse="true"</literal>. Instead, we could use the following mapping: - </para> - - <programlisting><![CDATA[<class name="Parent"> - <id name="id" column="parent_id"/> - .... - <map name="children"> - <key column="parent_id" - not-null="true"/> - <map-key column="name" - type="string"/> - <one-to-many class="Child"/> - </map> -</class> - -<class name="Child"> - <id name="id" column="child_id"/> - .... - <many-to-one name="parent" - class="Parent" - column="parent_id" - insert="false" - update="false" - not-null="true"/> -</class>]]></programlisting> - - <para> - Note that in this mapping, the collection-valued end of the association is responsible for - updates to the foreign key. TODO: Does this really result in some unnecessary update statements? - </para> - - </sect2> - - <sect2 id="collections-ternary"> - <title>Ternary associations</title> - - <para> - There are three possible approaches to mapping a ternary association. One is to use a - <literal>Map</literal> with an association as its index: - </para> - - <programlisting><![CDATA[<map name="contracts"> - <key column="employer_id" not-null="true"/> - <map-key-many-to-many column="employee_id" class="Employee"/> - <one-to-many class="Contract"/> -</map>]]></programlisting> - - <programlisting><![CDATA[<map name="connections"> - <key column="incoming_node_id"/> - <map-key-many-to-many column="outgoing_node_id" class="Node"/> - <many-to-many column="connection_id" class="Connection"/> -</map>]]></programlisting> - - <para> - A second approach is to simply remodel the association as an entity class. This - is the approach we use most commonly. - </para> - - <para> - A final alternative is to use composite elements, which we will discuss later. - </para> - - </sect2> - - <sect2 id="collections-idbag" revision="1"> - <title><literal>Using an &lt;idbag&gt;</literal></title> - - <para> - If you've fully embraced our view that composite keys are a bad thing and that - entities should have synthetic identifiers (surrogate keys), then you might - find it a bit odd that the many to many associations and collections of values - that we've shown so far all map to tables with composite keys! Now, this point - is quite arguable; a pure association table doesn't seem to benefit much from - a surrogate key (though a collection of composite values <emphasis>might</emphasis>). - Nevertheless, Hibernate provides a feature that allows you to map many to many - associations and collections of values to a table with a surrogate key. - </para> - - <para> - The <literal>&lt;idbag&gt;</literal> element lets you map a <literal>List</literal> - (or <literal>Collection</literal>) with bag semantics. - </para> - -<programlisting><![CDATA[<idbag name="lovers" table="LOVERS"> - <collection-id column="ID" type="long"> - <generator class="sequence"/> - </collection-id> - <key column="PERSON1"/> - <many-to-many column="PERSON2" class="Person" fetch="join"/> -</idbag>]]></programlisting> - - <para> - As you can see, an <literal>&lt;idbag&gt;</literal> has a synthetic id generator, - just like an entity class! A different surrogate key is assigned to each collection - row. Hibernate does not provide any mechanism to discover the surrogate key value - of a particular row, however. - </para> - - <para> - Note that the update performance of an <literal>&lt;idbag&gt;</literal> is - <emphasis>much</emphasis> better than a regular <literal>&lt;bag&gt;</literal>! - Hibernate can locate individual rows efficiently and update or delete them - individually, just like a list, map or set. - </para> - - <para> - In the current implementation, the <literal>native</literal> identifier generation - strategy is not supported for <literal>&lt;idbag&gt;</literal> collection identifiers. - </para> - - </sect2> - - </sect1> - - <!--undocumenting this stuff --> - - <!--sect1 id="collections-heterogeneous"> - <title>Heterogeneous Associations</title> - - <para> - The <literal>&lt;many-to-any&gt;</literal> and <literal>&lt;index-many-to-any&gt;</literal> - elements provide for true heterogeneous associations. These mapping elements work in the - same way as the <literal>&lt;any&gt;</literal> element - and should also be used - rarely, if ever. - </para> - - </sect1--> - - <sect1 id="collections-example" revision="1"> - <title>Collection examples</title> - - <para> - The previous sections are pretty confusing. So lets look at an example. This - class: - </para> - - <programlisting><![CDATA[package eg; -import java.util.Set; - -public class Parent { - private long id; - private Set children; - - public long getId() { return id; } - private void setId(long id) { this.id=id; } - - private Set getChildren() { return children; } - private void setChildren(Set children) { this.children=children; } - - .... - .... -}]]></programlisting> - - <para> - has a collection of <literal>Child</literal> instances. If each - child has at most one parent, the most natural mapping is a - one-to-many association: - </para> - - <programlisting><![CDATA[<hibernate-mapping> - - <class name="Parent"> - <id name="id"> - <generator class="sequence"/> - </id> - <set name="children"> - <key column="parent_id"/> - <one-to-many class="Child"/> - </set> - </class> - - <class name="Child"> - <id name="id"> - <generator class="sequence"/> - </id> - <property name="name"/> - </class> - -</hibernate-mapping>]]></programlisting> - - <para> - This maps to the following table definitions: - </para> - - <programlisting><![CDATA[create table parent ( id bigint not null primary key ) -create table child ( id bigint not null primary key, name varchar(255), parent_id bigint ) -alter table child add constraint childfk0 (parent_id) references parent]]></programlisting> - - <para> - If the parent is <emphasis>required</emphasis>, use a bidirectional one-to-many - association: - </para> - - <programlisting><![CDATA[<hibernate-mapping> - - <class name="Parent"> - <id name="id"> - <generator class="sequence"/> - </id> - <set name="children" inverse="true"> - <key column="parent_id"/> - <one-to-many class="Child"/> - </set> - </class> - - <class name="Child"> - <id name="id"> - <generator class="sequence"/> - </id> - <property name="name"/> - <many-to-one name="parent" class="Parent" column="parent_id" not-null="true"/> - </class> - -</hibernate-mapping>]]></programlisting> - - <para> - Notice the <literal>NOT NULL</literal> constraint: - </para> - - <programlisting><![CDATA[create table parent ( id bigint not null primary key ) -create table child ( id bigint not null - primary key, - name varchar(255), - parent_id bigint not null ) -alter table child add constraint childfk0 (parent_id) references parent]]></programlisting> - - <para> - Alternatively, if you absolutely insist that this association should be unidirectional, - you can declare the <literal>NOT NULL</literal> constraint on the <literal>&lt;key&gt;</literal> - mapping: - </para> - - <programlisting><![CDATA[<hibernate-mapping> - - <class name="Parent"> - <id name="id"> - <generator class="sequence"/> - </id> - <set name="children"> - <key column="parent_id" not-null="true"/> - <one-to-many class="Child"/> - </set> - </class> - - <class name="Child"> - <id name="id"> - <generator class="sequence"/> - </id> - <property name="name"/> - </class> - -</hibernate-mapping>]]></programlisting> - - <para> - On the other hand, if a child might have multiple parents, a many-to-many - association is appropriate: - </para> - - <programlisting><![CDATA[<hibernate-mapping> - - <class name="Parent"> - <id name="id"> - <generator class="sequence"/> - </id> - <set name="children" table="childset"> - <key column="parent_id"/> - <many-to-many class="Child" column="child_id"/> - </set> - </class> - - <class name="Child"> - <id name="id"> - <generator class="sequence"/> - </id> - <property name="name"/> - </class> - -</hibernate-mapping>]]></programlisting> - - <para> - Table definitions: - </para> - - <programlisting><![CDATA[create table parent ( id bigint not null primary key ) -create table child ( id bigint not null primary key, name varchar(255) ) -create table childset ( parent_id bigint not null, - child_id bigint not null, - primary key ( parent_id, child_id ) ) -alter table childset add constraint childsetfk0 (parent_id) references parent -alter table childset add constraint childsetfk1 (child_id) references child]]></programlisting> - - <para> - For more examples and a complete walk-through a parent/child relationship mapping, - see <xref linkend="example-parentchild"/>. - </para> - - <para> - Even more exotic association mappings are possible, we will catalog all possibilities - in the next chapter. - </para> - - </sect1> - -</chapter> Deleted: core/trunk/documentation/envers/src/main/docbook/en-US/content/component_mapping.xml =================================================================== --- core/trunk/documentation/envers/src/main/docbook/en-US/content/component_mapping.xml 2008-11-04 17:31:01 UTC (rev 15499) +++ core/trunk/documentation/envers/src/main/docbook/en-US/content/component_mapping.xml 2008-11-04 17:31:43 UTC (rev 15500) @@ -1,429 +0,0 @@ -<?xml version='1.0' encoding="UTF-8"?> -<!-- - ~ Hibernate, Relational Persistence for Idiomatic Java - ~ - ~ Copyright (c) 2008, Red Hat Middleware LLC or third-party contributors as - ~ indicated by the @author tags or express copyright attribution - ~ statements applied by the authors. All third-party contributions are - ~ distributed under license by Red Hat Middleware LLC. - ~ - ~ This copyrighted material is made available to anyone wishing to use, modify, - ~ copy, or redistribute it subject to the terms and conditions of the GNU - ~ Lesser General Public License, as published by the Free Software Foundation. - ~ - ~ This program is distributed in the hope that it will be useful, - ~ but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY - ~ or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License - ~ for more details. - ~ - ~ You should have received a copy of the GNU Lesser General Public License - ~ along with this distribution; if not, write to: - ~ Free Software Foundation, Inc. - ~ 51 Franklin Street, Fifth Floor - ~ Boston, MA 02110-1301 USA - --> - -<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd"> - -<chapter id="components"> - <title>Component Mapping</title> - - <para> - The notion of a <emphasis>component</emphasis> is re-used in several different contexts, - for different purposes, throughout Hibernate. - </para> - - <sect1 id="components-dependentobjects" revision="2" > - <title>Dependent objects</title> - - <para> - A component is a contained object that is persisted as a value type, not an entity - reference. The term "component" refers to the object-oriented notion of composition - (not to architecture-level components). For example, you might model a person like this: - </para> - - <programlisting><![CDATA[public class Person { - private java.util.Date birthday; - private Name name; - private String key; - public String getKey() { - return key; - } - private void setKey(String key) { - this.key=key; - } - public java.util.Date getBirthday() { - return birthday; - } - public void setBirthday(java.util.Date birthday) { - this.birthday = birthday; - } - public Name getName() { - return name; - } - public void setName(Name name) { - this.name = name; - } - ...... - ...... -}]]></programlisting> - -<programlisting><![CDATA[public class Name { - char initial; - String first; - String last; - public String getFirst() { - return first; - } - void setFirst(String first) { - this.first = first; - } - public String getLast() { - return last; - } - void setLast(String last) { - this.last = last; - } - public char getInitial() { - return initial; - } - void setInitial(char initial) { - this.initial = initial; - } -}]]></programlisting> - - <para> - Now <literal>Name</literal> may be persisted as a component of - <literal>Person</literal>. Notice that <literal>Name</literal> defines getter - and setter methods for its persistent properties, but doesn't need to declare - any interfaces or identifier properties. - </para> - - <para> - Our Hibernate mapping would look like: - </para> - - <programlisting><![CDATA[<class name="eg.Person" table="person"> - <id name="Key" column="pid" type="string"> - <generator class="uuid"/> - </id> - <property name="birthday" type="date"/> - <component name="Name" class="eg.Name"> <!-- class attribute optional --> - <property name="initial"/> - <property name="first"/> - <property name="last"/> - </component> -</class>]]></programlisting> - - <para> - The person table would have the columns <literal>pid</literal>, - <literal>birthday</literal>, - <literal>initial</literal>, - <literal>first</literal> and - <literal>last</literal>. - </para> - - <para> - Like all value types, components do not support shared references. In other words, two - persons could have the same name, but the two person objects would contain two independent - name ojects, only "the same" by value. The null value semantics of a component are - <emphasis>ad hoc</emphasis>. When reloading the containing object, Hibernate will assume - that if all component columns are null, then the entire component is null. This should - be okay for most purposes. - </para> - - <para> - The properties of a component may be of any Hibernate type (collections, many-to-one - associations, other components, etc). Nested components should <emphasis>not</emphasis> - be considered an exotic usage. Hibernate is intended to support a very fine-grained - object model. - </para> - - <para> - The <literal>&lt;component&gt;</literal> element allows a <literal>&lt;parent&gt;</literal> - subelement that maps a property of the component class as a reference back to the - containing entity. - </para> - - <programlisting><![CDATA[<class name="eg.Person" table="person"> - <id name="Key" column="pid" type="string"> - <generator class="uuid"/> - </id> - <property name="birthday" type="date"/> - <component name="Name" class="eg.Name" unique="true"> - <parent name="namedPerson"/> <!-- reference back to the Person --> - <property name="initial"/> - <property name="first"/> - <property name="last"/> - </component> -</class>]]></programlisting> - - </sect1> - - <sect1 id="components-incollections" revision="1"> - <title>Collections of dependent objects</title> - - <para> - Collections of components are supported (eg. an array of type - <literal>Name</literal>). Declare your component collection by - replacing the <literal>&lt;element&gt;</literal> tag with a - <literal>&lt;composite-element&gt;</literal> tag. - </para> - - <programlisting><![CDATA[<set name="someNames" table="some_names" lazy="true"> - <key column="id"/> - <composite-element class="eg.Name"> <!-- class attribute required --> - <property name="initial"/> - <property name="first"/> - <property name="last"/> - </composite-element> -</set>]]></programlisting> - - <para> - Note: if you define a <literal>Set</literal> of composite elements, it is - very important to implement <literal>equals()</literal> and - <literal>hashCode()</literal> correctly. - </para> - - <para> - Composite elements may contain components but not collections. If your - composite element itself contains - components, use the <literal>&lt;nested-composite-element&gt;</literal> - tag. This is a pretty exotic case - a collection of components which - themselves have components. By this stage you should be asking yourself - if a one-to-many association is more appropriate. Try remodelling the - composite element as an entity - but note that even though the Java model - is the same, the relational model and persistence semantics are still - slightly different. - </para> - - <para> - Please note that a composite element mapping doesn't support null-able properties - if you're using a <literal>&lt;set&gt;</literal>. Hibernate - has to use each columns value to identify a record when deleting objects - (there is no separate primary key column in the composite element table), - which is not possible with null values. You have to either use only - not-null properties in a composite-element or choose a - <literal>&lt;list&gt;</literal>, <literal>&lt;map&gt;</literal>, - <literal>&lt;bag&gt;</literal> or <literal>&lt;idbag&gt;</literal>. - </para> - - <para> - A special case of a composite element is a composite element with a nested - <literal>&lt;many-to-one&gt;</literal> element. A mapping like this allows - you to map extra columns of a many-to-many association table to the - composite element class. The following is a many-to-many association - from <literal>Order</literal> to <literal>Item</literal> where - <literal>purchaseDate</literal>, <literal>price</literal> and - <literal>quantity</literal> are properties of the association: - </para> - - <programlisting><![CDATA[<class name="eg.Order" .... > - .... - <set name="purchasedItems" table="purchase_items" lazy="true"> - <key column="order_id"> - <composite-element class="eg.Purchase"> - <property name="purchaseDate"/> - <property name="price"/> - <property name="quantity"/> - <many-to-one name="item" class="eg.Item"/> <!-- class attribute is optional --> - </composite-element> - </set> -</class>]]></programlisting> - - <para> - Of course, there can't be a reference to the purchae on the other side, for - bidirectional association navigation. Remember that components are value types and - don't allow shared references. A single <literal>Purchase</literal> can be in the - set of an <literal>Order</literal>, but it can't be referenced by the <literal>Item</literal> - at the same time. - </para> - - <para>Even ternary (or quaternary, etc) associations are possible:</para> - - <programlisting><![CDATA[<class name="eg.Order" .... > - .... - <set name="purchasedItems" table="purchase_items" lazy="true"> - <key column="order_id"> - <composite-element class="eg.OrderLine"> - <many-to-one name="purchaseDetails class="eg.Purchase"/> - <many-to-one name="item" class="eg.Item"/> - </composite-element> - </set> -</class>]]></programlisting> - - <para> - Composite elements may appear in queries using the same syntax as - associations to other entities. - </para> - - </sect1> - - <sect1 id="components-asmapindex"> - <title>Components as Map indices</title> - - <para> - The <literal>&lt;composite-map-key&gt;</literal> element lets you map a - component class as the key of a <literal>Map</literal>. Make sure you override - <literal>hashCode()</literal> and <literal>equals()</literal> correctly on - the component class. - </para> - </sect1> - - <sect1 id="components-compositeid" revision="1"> - <title>Components as composite identifiers</title> - - <para> - You may use a component as an identifier of an entity class. Your component - class must satisfy certain requirements: - </para> - - <itemizedlist spacing="compact"> - <listitem> - <para> - It must implement <literal>java.io.Serializable</literal>. - </para> - </listitem> - <listitem> - <para> - It must re-implement <literal>equals()</literal> and - <literal>hashCode()</literal>, consistently with the database's - notion of composite key equality. - </para> - </listitem> - </itemizedlist> - - <para> - <emphasis>Note: in Hibernate3, the second requirement is not an absolutely hard - requirement of Hibernate. But do it anyway.</emphasis> - </para> - - <para> - You can't use an <literal>IdentifierGenerator</literal> to generate composite keys. - Instead the application must assign its own identifiers. - </para> - - <para> - Use the <literal>&lt;composite-id&gt;</literal> tag (with nested - <literal>&lt;key-property&gt;</literal> elements) in place of the usual - <literal>&lt;id&gt;</literal> declaration. For example, the - <literal>OrderLine</literal> class has a primary key that depends upon - the (composite) primary key of <literal>Order</literal>. - </para> - - <programlisting><![CDATA[<class name="OrderLine"> - - <composite-id name="id" class="OrderLineId"> - <key-property name="lineId"/> - <key-property name="orderId"/> - <key-property name="customerId"/> - </composite-id> - - <property name="name"/> - - <many-to-one name="order" class="Order" - insert="false" update="false"> - <column name="orderId"/> - <column name="customerId"/> - </many-to-one> - .... - -</class>]]></programlisting> - - <para> - Now, any foreign keys referencing the <literal>OrderLine</literal> table are also - composite. You must declare this in your mappings for other classes. An association - to <literal>OrderLine</literal> would be mapped like this: - </para> - - <programlisting><![CDATA[<many-to-one name="orderLine" class="OrderLine"> -<!-- the "class" attribute is optional, as usual --> - <column name="lineId"/> - <column name="orderId"/> - <column name="customerId"/> -</many-to-one>]]></programlisting> - - <para> - (Note that the <literal>&lt;column&gt;</literal> tag is an alternative to the - <literal>column</literal> attribute everywhere.) - </para> - - <para> - A <literal>many-to-many</literal> association to <literal>OrderLine</literal> also - uses the composite foreign key: - </para> - - <programlisting><![CDATA[<set name="undeliveredOrderLines"> - <key column name="warehouseId"/> - <many-to-many class="OrderLine"> - <column name="lineId"/> - <column name="orderId"/> - <column name="customerId"/> - </many-to-many> -</set>]]></programlisting> - - <para> - The collection of <literal>OrderLine</literal>s in <literal>Order</literal> would - use: - </para> - - <programlisting><![CDATA[<set name="orderLines" inverse="true"> - <key> - <column name="orderId"/> - <column name="customerId"/> - </key> - <one-to-many class="OrderLine"/> -</set>]]></programlisting> - - <para> - (The <literal>&lt;one-to-many&gt;</literal> element, as usual, declares no columns.) - </para> - - <para> - If <literal>OrderLine</literal> itself owns a collection, it also has a composite - foreign key. - </para> - - <programlisting><![CDATA[<class name="OrderLine"> - .... - .... - <list name="deliveryAttempts"> - <key> <!-- a collection inherits the composite key type --> - <column name="lineId"/> - <column name="orderId"/> - <column name="customerId"/> - </key> - <list-index column="attemptId" base="1"/> - <composite-element class="DeliveryAttempt"> - ... - </composite-element> - </set> -</class>]]></programlisting> - - </sect1> - - <sect1 id="components-dynamic" revision="1"> - <title>Dynamic components</title> - - <para> - You may even map a property of type <literal>Map</literal>: - </para> - - <programlisting><![CDATA[<dynamic-component name="userAttributes"> - <property name="foo" column="FOO" type="string"/> - <property name="bar" column="BAR" type="integer"/> - <many-to-one name="baz" class="Baz" column="BAZ_ID"/> -</dynamic-component>]]></programlisting> - - <para> - The semantics of a <literal>&lt;dynamic-component&gt;</literal> mapping are identical - to <literal>&lt;component&gt;</literal>. The advantage of this kind of mapping is - the ability to determine the actual properties of the bean at deployment time, just - by editing the mapping document. Runtime manipulation of the mapping document is - also possible, using a DOM parser. Even better, you can access (and change) Hibernate's - configuration-time metamodel via the <literal>Configuration</literal> object. - </para> - - </sect1> - -</chapter> Deleted: core/trunk/documentation/envers/src/main/docbook/en-US/content/configuration.xml =================================================================== --- core/trunk/documentation/envers/src/main/docbook/en-US/content/configuration.xml 2008-11-04 17:31:01 UTC (rev 15499) +++ core/trunk/documentation/envers/src/main/docbook/en-US/content/configuration.xml 2008-11-04 17:31:43 UTC (rev 15500) @@ -1,1759 +0,0 @@ -<?xml version='1.0' encoding="UTF-8"?> -<!-- - ~ Hibernate, Relational Persistence for Idiomatic Java - ~ - ~ Copyright (c) 2008, Red Hat Middleware LLC or third-party contributors as - ~ indicated by the @author tags or express copyright attribution - ~ statements applied by the authors. All third-party contributions are - ~ distributed under license by Red Hat Middleware LLC. - ~ - ~ This copyrighted material is made available to anyone wishing to use, modify, - ~ copy, or redistribute it subject to the terms and conditions of the GNU - ~ Lesser General Public License, as published by the Free Software Foundation. - ~ - ~ This program is distributed in the hope that it will be useful, - ~ but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY - ~ or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License - ~ for more details. - ~ - ~ You should have received a copy of the GNU Lesser General Public License - ~ along with this distribution; if not, write to: - ~ Free Software Foundation, Inc. - ~ 51 Franklin Street, Fifth Floor - ~ Boston, MA 02110-1301 USA - --> - -<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd"> - -<chapter id="session-configuration" revision="1"> - <title>Configuration</title> - - <para> - Because Hibernate is designed to operate in many different environments, there - are a large number of configuration parameters. Fortunately, most have sensible - default values and Hibernate is distributed with an example - <literal>hibernate.properties</literal> file in <literal>etc/</literal> that shows - the various options. Just put the example file in your classpath and customize it. - </para> - - <sect1 id="configuration-programmatic" revision="1"> - <title>Programmatic configuration</title> - - <para> - An instance of <classname>org.hibernate.cfg.Configuration</classname> represents an entire set of mappings - of an application's Java types to an SQL database. The <classname>org.hibernate.cfg.Configuration</classname> - is used to build an (immutable) <interfacename>org.hibernate.SessionFactory</interfacename>. The mappings - are compiled from various XML mapping files. - </para> - - <para> - You may obtain a <classname>org.hibernate.cfg.Configuration</classname> instance by instantiating - it directly and specifying XML mapping documents. If the mapping files are in the classpath, - use <literal>addResource()</literal>: - </para> - - <programlisting><![CDATA[Configuration cfg = new Configuration() - .addResource("Item.hbm.xml") - .addResource("Bid.hbm.xml");]]></programlisting> - - <para> - An alternative (sometimes better) way is to specify the mapped class, and - let Hibernate find the mapping document for you: - </para> - - <programlisting><![CDATA[Configuration cfg = new Configuration() - .addClass(org.hibernate.auction.Item.class) - .addClass(org.hibernate.auction.Bid.class);]]></programlisting> - - <para> - Then Hibernate will look for mapping files named <filename>/org/hibernate/auction/Item.hbm.xml</filename> - and <filename>/org/hibernate/auction/Bid.hbm.xml</filename> in the classpath. This approach eliminates any - hardcoded filenames. - </para> - - <para> - A <classname>org.hibernate.cfg.Configuration</classname> also allows you to specify configuration - properties: - </para> - - <programlisting><![CDATA[Configuration cfg = new Configuration() - .addClass(org.hibernate.auction.Item.class) - .addClass(org.hibernate.auction.Bid.class) - .setProperty("hibernate.dialect", "org.hibernate.dialect.MySQLInnoDBDialect") - .setProperty("hibernate.connection.datasource", "java:comp/env/jdbc/test") - .setProperty("hibernate.order_updates", "true");]]></programlisting> - - <para> - This is not the only way to pass configuration properties to Hibernate. - The various options include: - </para> - - <orderedlist spacing="compact"> - <listitem> - <para> - Pass an instance of <classname>java.util.Properties</classname> to - <literal>Configuration.setProperties()</literal>. - </para> - </listitem> - <listitem> - <para> - Place a file named <filename>hibernate.properties</filename> in a root directory of the classpath. - </para> - </listitem> - <listitem> - <para> - Set <literal>System</literal> properties using <literal>java -Dproperty=value</literal>. - </para> - </listitem> - <listitem> - <para> - Include <literal>&lt;property&gt;</literal> elements in - <literal>hibernate.cfg.xml</literal> (discussed later). - </para> - </listitem> - </orderedlist> - - <para> - <filename>hibernate.properties</filename> is the easiest approach if you want to get started quickly. - </para> - - <para> - The <classname>org.hibernate.cfg.Configuration</classname> is intended as a startup-time object, - to be discarded once a <literal>SessionFactory</literal> is created. - </para> - - </sect1> - - <sect1 id="configuration-sessionfactory"> - <title>Obtaining a SessionFactory</title> - - <para> - When all mappings have been parsed by the <classname>org.hibernate.cfg.Configuration</classname>, - the application must obtain a factory for <interfacename>org.hibernate.Session</interfacename> instances. - This factory is intended to be shared by all application threads: - </para> - - <programlisting><![CDATA[SessionFactory sessions = cfg.buildSessionFactory();]]></programlisting> - - <para> - Hibernate does allow your application to instantiate more than one - <interfacename>org.hibernate.SessionFactory</interfacename>. This is useful if you are using more than - one database. - </para> - - </sect1> - - <sect1 id="configuration-hibernatejdbc" revision="1"> - <title>JDBC connections</title> - - <para> - Usually, you want to have the <interfacename>org.hibernate.SessionFactory</interfacename> create and pool - JDBC connections for you. If you take this approach, opening a <interfacename>org.hibernate.Session</interfacename> - is as simple as: - </para> - - <programlisting><![CDATA[Session session = sessions.openSession(); // open a new Session]]></programlisting> - - <para> - As soon as you do something that requires access to the database, a JDBC connection will be obtained from - the pool. - </para> - - <para> - For this to work, we need to pass some JDBC connection properties to Hibernate. All Hibernate property - names and semantics are defined on the class <classname>org.hibernate.cfg.Environment</classname>. We will - now describe the most important settings for JDBC connection configuration. - </para> - - <para> - Hibernate will obtain (and pool) connections using <classname>java.sql.DriverManager</classname> - if you set the following properties: - </para> - - <table frame="topbot"> - <title>Hibernate JDBC Properties</title> - <tgroup cols="2"> - <colspec colname="c1" colwidth="1*"/> - <colspec colname="c2" colwidth="1*"/> - <thead> - <row> - <entry>Property name</entry> - <entry>Purpose</entry> - </row> - </thead> - <tbody> - <row> - <entry> - <property>hibernate.connection.driver_class</property> - </entry> - <entry> - <emphasis>JDBC driver class</emphasis> - </entry> - </row> - <row> - <entry> - <property>hibernate.connection.url</property> - </entry> - <entry> - <emphasis>JDBC URL</emphasis> - </entry> - </row> - <row> - <entry> - <property>hibernate.connection.username</property> - </entry> - <entry> - <emphasis>database user</emphasis> - </entry> - </row> - <row> - <entry> - <property>hibernate.connection.password</property> - </entry> - <entry> - <emphasis>database user password</emphasis> - </entry> - </row> - <row> - <entry> - <property>hibernate.connection.pool_size</property> - </entry> - <entry> - <emphasis>maximum number of pooled connections</emphasis> - </entry> - </row> - </tbody> - </tgroup> - </table> - - <para> - Hibernate's own connection pooling algorithm is however quite rudimentary. - It is intended to help you get started and is <emphasis>not intended for use - in a production system</emphasis> or even for performance testing. You should - use a third party pool for best performance and stability. Just replace the - <property>hibernate.connection.pool_size</property> property with connection - pool specific settings. This will turn off Hibernate's internal pool. For - example, you might like to use C3P0. - </para> - - <para> - C3P0 is an open source JDBC connection pool distributed along with Hibernate in the <filename>lib</filename> - directory. Hibernate will use its <classname>org.hibernate.connection.C3P0ConnectionProvider</classname> - for connection pooling if you set <property>hibernate.c3p0.*</property> properties. If you'd like to use Proxool - refer to the packaged <filename>hibernate.properties</filename> and the Hibernate web site for more - information. - </para> - - <para> - Here is an example <filename>hibernate.properties</filename> file for C3P0: - </para> - - <programlisting id="c3p0-configuration" revision="1"><![CDATA[hibernate.connection.driver_class = org.postgresql.Driver -hibernate.connection.url = jdbc:postgresql://localhost/mydatabase -hibernate.connection.username = myuser -hibernate.connection.password = secret -hibernate.c3p0.min_size=5 -hibernate.c3p0.max_size=20 -hibernate.c3p0.timeout=1800 -hibernate.c3p0.max_statements=50 -hibernate.dialect = org.hibernate.dialect.PostgreSQLDialect]]></programlisting> - - <para> - For use inside an application server, you should almost always configure Hibernate to obtain connections - from an application server <interfacename>javax.sql.Datasource</interfacename> registered in JNDI. You'll - need to set at least one of the following properties: - </para> - - <table frame="topbot"> - <title>Hibernate Datasource Properties</title> - <tgroup cols="2"> - <colspec colname="c1" colwidth="1*"/> - <colspec colname="c2" colwidth="1*"/> - <thead> - <row> - <entry>Property name</entry> - <entry>Purpose</entry> - </row> - </thead> - <tbody> - <row> - <entry> - <property>hibernate.connection.datasource</property> - </entry> - <entry> - <emphasis>datasource JNDI name</emphasis> - </entry> - </row> - <row> - <entry> - <property>hibernate.jndi.url</property> - </entry> - <entry> - <emphasis>URL of the JNDI provider</emphasis> (optional) - </entry> - </row> - <row> - <entry> - <property>hibernate.jndi.class</property> - </entry> - <entry> - <emphasis>class of the JNDI <literal>InitialContextFactory</literal></emphasis> (optional) - </entry> - </row> - <row> - <entry> - <property>hibernate.connection.username</property> - </entry> - <entry> - <emphasis>database user</emphasis> (optional) - </entry> - </row> - <row> - <entry> - <property>hibernate.connection.password</property> - </entry> - <entry> - <emphasis>database user password</emphasis> (optional) - </entry> - </row> - </tbody> - </tgroup> - </table> - - <para> - Here's an example <filename>hibernate.properties</filename> file for an application server provided JNDI - datasource: - </para> - - <programlisting><![CDATA[hibernate.connection.datasource = java:/comp/env/jdbc/test -hibernate.transaction.factory_class = \ - org.hibernate.transaction.JTATransactionFactory -hibernate.transaction.manager_lookup_class = \ - org.hibernate.transaction.JBossTransactionManagerLookup -hibernate.dialect = org.hibernate.dialect.PostgreSQLDialect]]></programlisting> - - <para> - JDBC connections obtained from a JNDI datasource will automatically participate - in the container-managed transactions of the application server. - </para> - - <para> - Arbitrary connection properties may be given by prepending "<literal>hibernate.connection</literal>" to the - connection property name. For example, you may specify a <property>charSet</property> - connection property using <property>hibernate.connection.charSet</property>. - </para> - - <para> - You may define your own plugin strategy for obtaining JDBC connections by implementing the - interface <interfacename>org.hibernate.connection.ConnectionProvider</interfacename>, and specifying your - custom implementation via the <property>hibernate.connection.provider_class</property> property. - </para> - - </sect1> - - <sect1 id="configuration-optional" revision="1"> - <title>Optional configuration properties</title> - - <para> - There are a number of other properties that control the behaviour of Hibernate at runtime. All are optional - and have reasonable default values. - </para> - - <para> - <emphasis>Warning: some of these properties are "system-level" only.</emphasis> System-level properties can - be set only via <literal>java -Dproperty=value</literal> or <filename>hibernate.properties</filename>. They - may <emphasis>not</emphasis> be set by the other techniques described above. - </para> - - <table frame="topbot" id="configuration-optional-properties" revision="8"> - <title>Hibernate Configuration Properties</title> - <tgroup cols="2"> - <colspec colname="c1" colwidth="1*"/> - <colspec colname="c2" colwidth="1*"/> - <thead> - <row> - <entry>Property name</entry> - <entry>Purpose</entry> - </row> - </thead> - <tbody> - <row> - <entry> - <property>hibernate.dialect</property> - </entry> - <entry> - The classname of a Hibernate <classname>org.hibernate.dialect.Dialect</classname> which - allows Hibernate to generate SQL optimized for a particular relational database. - <para> - <emphasis role="strong">eg.</emphasis> - <literal>full.classname.of.Dialect</literal> - </para> - <para> - In most cases Hibernate will actually be able to chose the correct - <classname>org.hibernate.dialect.Dialect</classname> implementation to use based on the - <literal>JDBC metadata</literal> returned by the JDBC driver. - </para> - </entry> - </row> - <row> - <entry> - <property>hibernate.show_sql</property> - </entry> - <entry> - Write all SQL statements to console. This is an alternative - to setting the log category <literal>org.hibernate.SQL</literal> - to <literal>debug</literal>. - <para> - <emphasis role="strong">eg.</emphasis> - <literal>true</literal> | <literal>false</literal> - </para> - </entry> - </row> - <row> - <entry> - <property>hibernate.format_sql</property> - </entry> - <entry> - Pretty print the SQL in the log and console. - <para> - <emphasis role="strong">eg.</emphasis> - <literal>true</literal> | <literal>false</literal> - </para> - </entry> - </row> - <row> - <entry> - <property>hibernate.default_schema</property> - </entry> - <entry> - Qualify unqualified table names with the given schema/tablespace - in generated SQL. - <para> - <emphasis role="strong">eg.</emphasis> - <literal>SCHEMA_NAME</literal> - </para> - </entry> - </row> - <row> - <entry> - <property>hibernate.default_catalog</property> - </entry> - <entry> - Qualify unqualified table names with the given catalog - in generated SQL. - <para> - <emphasis role="strong">eg.</emphasis> - <literal>CATALOG_NAME</literal> - </para> - </entry> - </row> - <row> - <entry> - <property>hibernate.session_factory_name</property> - </entry> - <entry> - The <interfacename>org.hibernate.SessionFactory</interfacename> will be automatically - bound to this name in JNDI after it has been created. - <para> - <emphasis role="strong">eg.</emphasis> - <literal>jndi/composite/name</literal> - </para> - </entry> - </row> - <row> - <entry> - <property>hibernate.max_fetch_depth</property> - </entry> - <entry> - Set a maximum "depth" for the outer join fetch tree - for single-ended associations (one-to-one, many-to-one). - A <literal>0</literal> disables default outer join fetching. - <para> - <emphasis role="strong">eg.</emphasis> - recommended values between <literal>0</literal> and - <literal>3</literal> - </para> - </entry> - </row> - <row> - <entry> - <property>hibernate.default_batch_fetch_size</property> - </entry> - <entry> - Set a default size for Hibernate batch fetching of associations. - <para> - <emphasis role="strong">eg.</emphasis> - recommended values <literal>4</literal>, <literal>8</literal>, - <literal>16</literal> - </para> - </entry> - </row> - <row> - <entry> - <property>hibernate.default_entity_mode</property> - </entry> - <entry> - Set a default mode for entity representation for all sessions - opened from this <literal>SessionFactory</literal> - <para> - <literal>dynamic-map</literal>, <literal>dom4j</literal>, - <literal>pojo</literal> - </para> - </entry> - </row> - <row> - <entry> - <property>hibernate.order_updates</property> - </entry> - <entry> - Force Hibernate to order SQL updates by the primary key value - of the items being updated. This will result in fewer transaction - deadlocks in highly concurrent systems. - <para> - <emphasis role="strong">eg.</emphasis> - <literal>true</literal> | <literal>false</literal> - </para> - </entry> - </row> - <row> - <entry> - <property>hibernate.generate_statistics</property> - </entry> - <entry> - If enabled, Hibernate will collect statistics useful for - performance tuning. - <para> - <emphasis role="strong">eg.</emphasis> - <literal>true</literal> | <literal>false</literal> - </para> - </entry> - </row> - <row> - <entry> - <property>hibernate.use_identifier_rollback</property> - </entry> - <entry> - If enabled, generated identifier properties will be - reset to default values when objects are deleted. - <para> - <emphasis role="strong">eg.</emphasis> - <literal>true</literal> | <literal>false</literal> - </para> - </entry> - </row> - <row> - <entry> - <property>hibernate.use_sql_comments</property> - </entry> - <entry> - If turned on, Hibernate will generate comments inside the SQL, for - easier debugging, defaults to <literal>false</literal>. - <para> - <emphasis role="strong">eg.</emphasis> - <literal>true</literal> | <literal>false</literal> - </para> - </entry> - </row> - </tbody> - </tgroup> - </table> - - <table frame="topbot" id="configuration-jdbc-properties" revision="8"> - <title>Hibernate JDBC and Connection Properties</title> - <tgroup cols="2"> -<!-- - <colspec colname="c1" colwidth="1*"/> - <colspec colname="c2" colwidth="1*"/> ---> - <thead> - <row> - <entry>Property name</entry> - <entry>Purpose</entry> - </row> - </thead> - <tbody> - <row> - <entry> - <property>hibernate.jdbc.fetch_size</property> - </entry> - <entry> - A non-zero value determines the JDBC fetch size (calls - <literal>Statement.setFetchSize()</literal>). - </entry> - </row> - <row> - <entry> - <property>hibernate.jdbc.batch_size</property> - </entry> - <entry> - A non-zero value enables use of JDBC2 batch updates by Hibernate. - <para> - <emphasis role="strong">eg.</emphasis> - recommended values between <literal>5</literal> and <literal>30</literal> - </para> - </entry> - </row> - <row> - <entry> - <property>hibernate.jdbc.batch_versioned_data</property> - </entry> - <entry> - Set this property to <literal>true</literal> if your JDBC driver returns - correct row counts from <literal>executeBatch()</literal> (it is usually - safe to turn this option on). Hibernate will then use batched DML for - automatically versioned data. Defaults to <literal>false</literal>. - <para> - <emphasis role="strong">eg.</emphasis> - <literal>true</literal> | <literal>false</literal> - </para> - </entry> - </row> - <row> - <entry> - <property>hibernate.jdbc.factory_class</property> - </entry> - <entry> - Select a custom <interfacename>org.hibernate.jdbc.Batcher</interfacename>. Most applications - will not need this configuration property. - <para> - <emphasis role="strong">eg.</emphasis> - <literal>classname.of.BatcherFactory</literal> - </para> - </entry> - </row> - <row> - <entry> - <property>hibernate.jdbc.use_scrollable_resultset</property> - </entry> - <entry> - Enables use of JDBC2 scrollable resultsets by Hibernate. - This property is only necessary when using user supplied - JDBC connections, Hibernate uses connection metadata otherwise. - <para> - <emphasis role="strong">eg.</emphasis> - <literal>true</literal> | <literal>false</literal> - </para> - </entry> - </row> - <row> - <entry> - <property>hibernate.jdbc.use_streams_for_binary</property> - </entry> - <entry> - Use streams when writing/reading <literal>binary</literal> or <literal>serializable</literal> - types to/from JDBC. <emphasis>*system-level property*</emphasis> - <para> - <emphasis role="strong">eg.</emphasis> - <literal>true</literal> | <literal>false</literal> - </para> - </entry> - </row> - <row> - <entry> - <property>hibernate.jdbc.use_get_generated_keys</property> - </entry> - <entry> - Enable use of JDBC3 <literal>PreparedStatement.getGeneratedKeys()</literal> - to retrieve natively generated keys after insert. Requires JDBC3+ driver - and JRE1.4+, set to false if your driver has problems with the Hibernate - identifier generators. By default, tries to determine the driver capabilities - using connection metadata. - <para> - <emphasis role="strong">eg.</emphasis> - <literal>true|false</literal> - </para> - </entry> - </row> - <row> - <entry> - <property>hibernate.connection.provider_class</property> - </entry> - <entry> - The classname of a custom <interfacename>org.hibernate.connection.ConnectionProvider</interfacename> - which provides JDBC connections to Hibernate. - <para> - <emphasis role="strong">eg.</emphasis> - <literal>classname.of.ConnectionProvider</literal> - </para> - </entry> - </row> - <row> - <entry> - <property>hibernate.connection.isolation</property> - </entry> - <entry> - Set the JDBC transaction isolation level. Check <interfacename>java.sql.Connection</interfacename> - for meaningful values but note that most databases do not support all isolation levels and some - define additional, non-standard isolations. - <para> - <emphasis role="strong">eg.</emphasis> - <literal>1, 2, 4, 8</literal> - </para> - </entry> - </row> - <row> - <entry> - <property>hibernate.connection.autocommit</property> - </entry> - <entry> - Enables autocommit for JDBC pooled connections (not recommended). - <para> - <emphasis role="strong">eg.</emphasis> - <literal>true</literal> | <literal>false</literal> - </para> - </entry> - </row> - <row> - <entry> - <property>hibernate.connection.release_mode</property> - </entry> - <entry> - Specify when Hibernate should release JDBC connections. By default, - a JDBC connection is held until the session is explicitly closed or - disconnected. For an application server JTA datasource, you should use - <literal>after_statement</literal> to aggressively release connections - after every JDBC call. For a non-JTA connection, it often makes sense to - release the connection at the end of each transaction, by using - <literal>after_transaction</literal>. <literal>auto</literal> will - choose <literal>after_statement</literal> for the JTA and CMT transaction - strategies and <literal>after_transaction</literal> for the JDBC - transaction strategy. - <para> - <emphasis role="strong">eg.</emphasis> - <literal>auto</literal> (default) | <literal>on_close</literal> | - <literal>after_transaction</literal> | <literal>after_statement</literal> - </para> - <para> - Note that this setting only affects <literal>Session</literal>s returned from - <literal>SessionFactory.openSession</literal>. For <literal>Session</literal>s - obtained through <literal>SessionFactory.getCurrentSession</literal>, the - <literal>CurrentSessionContext</literal> implementation configured for use - controls the connection release mode for those <literal>Session</literal>s. - See <xref linkend="architecture-current-session"/> - </para> - </entry> - </row> - <row> - <entry> - <property>hibernate.connection.</property><emphasis>&lt;propertyName&gt;</emphasis> - </entry> - <entry> - Pass the JDBC property <emphasis>&lt;propertyName&gt;</emphasis> - to <literal>DriverManager.getConnection()</literal>. - </entry> - </row> - <row> - <entry> - <property>hibernate.jndi.</property><emphasis>&lt;propertyName&gt;</emphasis> - </entry> - <entry> - Pass the property <emphasis>&lt;propertyName&gt;</emphasis> to - the JNDI <literal>InitialContextFactory</literal>. - </entry> - </row> - </tbody> - </tgroup> - </table> - - <table frame="topbot" id="configuration-cache-properties" revision="7"> - <title>Hibernate Cache Properties</title> - <tgroup cols="2"> - <colspec colname="c1" colwidth="1*"/> - <colspec colname="c2" colwidth="1*"/> - <thead> - <row> - <entry>Property name</entry> - <entry>Purpose</entry> - </row> - </thead> - <tbody> - <row> - <entry> - <literal>hibernate.cache.provider_class</literal> - </entry> - <entry> - The classname of a custom <literal>CacheProvider</literal>. - <para> - <emphasis role="strong">eg.</emphasis> - <literal>classname.of.CacheProvider</literal> - </para> - </entry> - </row> - <row> - <entry> - <literal>hibernate.cache.use_minimal_puts</literal> - </entry> - <entry> - Optimize second-level cache operation to minimize writes, at the - cost of more frequent reads. This setting is most useful for - clustered caches and, in Hibernate3, is enabled by default for - clustered cache implementations. - <para> - <emphasis role="strong">eg.</emphasis> - <literal>true|false</literal> - </para> - </entry> - </row> - <row> - <entry> - <literal>hibernate.cache.use_query_cache</literal> - </entry> - <entry> - Enable the query cache, individual queries still have to be set cachable. - <para> - <emphasis role="strong">eg.</emphasis> - <literal>true|false</literal> - </para> - </entry> - </row> - <row> - <entry> - <literal>hibernate.cache.use_second_level_cache</literal> - </entry> - <entry> - May be used to completely disable the second level cache, which is enabled - by default for classes which specify a <literal>&lt;cache&gt;</literal> - mapping. - <para> - <emphasis role="strong">eg.</emphasis> - <literal>true|false</literal> - </para> - </entry> - </row> - <row> - <entry> - <literal>hibernate.cache.query_cache_factory</literal> - </entry> - <entry> - The classname of a custom <literal>QueryCache</literal> interface, - defaults to the built-in <literal>StandardQueryCache</literal>. - <para> - <emphasis role="strong">eg.</emphasis> - <literal>classname.of.QueryCache</literal> - </para> - </entry> - </row> - <row> - <entry> - <literal>hibernate.cache.region_prefix</literal> - </entry> - <entry> - A prefix to use for second-level cache region names. - <para> - <emphasis role="strong">eg.</emphasis> - <literal>prefix</literal> - </para> - </entry> - </row> - <row> - <entry> - <literal>hibernate.cache.use_structured_entries</literal> - </entry> - <entry> - Forces Hibernate to store data in the second-level cache - in a more human-friendly format. - <para> - <emphasis role="strong">eg.</emphasis> - <literal>true|false</literal> - </para> - </entry> - </row> - </tbody> - </tgroup> - </table> - - <table frame="topbot" id="configuration-transaction-properties" revision="9"> - <title>Hibernate Transaction Properties</title> - <tgroup cols="2"> - <colspec colname="c1" colwidth="1*"/> - <colspec colname="c2" colwidth="1*"/> - <thead> - <row> - <entry>Property name</entry> - <entry>Purpose</entry> - </row> - </thead> - <tbody> - <row> - <entry> - <literal>hibernate.transaction.factory_class</literal> - </entry> - <entry> - The classname of a <literal>TransactionFactory</literal> - to use with Hibernate <literal>Transaction</literal> API - (defaults to <literal>JDBCTransactionFactory</literal>). - <para> - <emphasis role="strong">eg.</emphasis> - <literal>classname.of.TransactionFactory</literal> - </para> - </entry> - </row> - <row> - <entry> - <literal>jta.UserTransaction</literal> - </entry> - <entry> - A JNDI name used by <literal>JTATransactionFactory</literal> to - obtain the JTA <literal>UserTransaction</literal> from the - application server. - <para> - <emphasis role="strong">eg.</emphasis> - <literal>jndi/composite/name</literal> - </para> - </entry> - </row> - <row> - <entry> - <literal>hibernate.transaction.manager_lookup_class</literal> - </entry> - <entry> - The classname of a <literal>TransactionManagerLookup</literal> - - required when JVM-level caching is enabled or when using hilo - generator in a JTA environment. - <para> - <emphasis role="strong">eg.</emphasis> - <literal>classname.of.TransactionManagerLookup</literal> - </para> - </entry> - </row> - <row> - <entry> - <literal>hibernate.transaction.flush_before_completion</literal> - </entry> - <entry> - If enabled, the session will be automatically flushed during the - before completion phase of the transaction. Built-in and - automatic session context management is preferred, see - <xref linkend="architecture-current-session"/>. - <para> - <emphasis role="strong">eg.</emphasis> - <literal>true</literal> | <literal>false</literal> - </para> - </entry> - </row> - <row> - <entry> - <literal>hibernate.transaction.auto_close_session</literal> - </entry> - <entry> - If enabled, the session will be automatically closed during the - after completion phase of the transaction. Built-in and - utomatic session context management is preferred, see - <xref linkend="architecture-current-session"/>. - <para> - <emphasis role="strong">eg.</emphasis> - <literal>true</literal> | <literal>false</literal> - </para> - </entry> - </row> - </tbody> - </tgroup> - </table> - - <table frame="topbot" id="configuration-misc-properties" revision="10"> - <title>Miscellaneous Properties</title> - <tgroup cols="2"> - <colspec colname="c1" colwidth="1*"/> - <colspec colname="c2" colwidth="1*"/> - <thead> - <row> - <entry>Property name</entry> - <entry>Purpose</entry> - </row> - </thead> - <tbody> - <row> - <entry> - <literal>hibernate.current_session_context_class</literal> - </entry> - <entry> - Supply a (custom) strategy for the scoping of the "current" - <literal>Session</literal>. See - <xref linkend="architecture-current-session"/> for more - information about the built-in strategies. - <para> - <emphasis role="strong">eg.</emphasis> - <literal>jta</literal> | <literal>thread</literal> | - <literal>managed</literal> | <literal>custom.Class</literal> - </para> - </entry> - </row> - <row> - <entry> - <literal>hibernate.query.factory_class</literal> - </entry> - <entry> - Chooses the HQL parser implementation. - <para> - <emphasis role="strong">eg.</emphasis> - <literal>org.hibernate.hql.ast.ASTQueryTranslatorFactory</literal> or - <literal>org.hibernate.hql.classic.ClassicQueryTranslatorFactory</literal> - </para> - </entry> - </row> - <row> - <entry> - <literal>hibernate.query.substitutions</literal> - </entry> - <entry> - Mapping from tokens in Hibernate queries to SQL tokens - (tokens might be function or literal names, for example). - <para> - <emphasis role="strong">eg.</emphasis> - <literal>hqlLiteral=SQL_LITERAL, hqlFunction=SQLFUNC</literal> - </para> - </entry> - </row> - <row> - <entry> - <literal>hibernate.hbm2ddl.auto</literal> - </entry> - <entry> - Automatically validate or export schema DDL to the database - when the <literal>SessionFactory</literal> is created. With - <literal>create-drop</literal>, the database schema will be - dropped when the <literal>SessionFactory</literal> is closed - explicitly. - <para> - <emphasis role="strong">eg.</emphasis> - <literal>validate</literal> | <literal>update</literal> | - <literal>create</literal> | <literal>create-drop</literal> - </para> - </entry> - </row> - <row> - <entry> - <literal>hibernate.cglib.use_reflection_optimizer</literal> - </entry> - <entry> - Enables use of CGLIB instead of runtime reflection (System-level - property). Reflection can sometimes be useful when troubleshooting, - note that Hibernate always requires CGLIB even if you turn off the - optimizer. You can not set this property in <literal>hibernate.cfg.xml</literal>. - <para> - <emphasis role="strong">eg.</emphasis> - <literal>true</literal> | <literal>false</literal> - </para> - </entry> - </row> - </tbody> - </tgroup> - </table> - - <sect2 id="configuration-optional-dialects" revision="1"> - <title>SQL Dialects</title> - - <para> - You should always set the <literal>hibernate.dialect</literal> property to the correct - <literal>org.hibernate.dialect.Dialect</literal> subclass for your database. If you - specify a dialect, Hibernate will use sensible defaults for some of the - other properties listed above, saving you the effort of specifying them manually. - </para> - - <table frame="topbot" id="sql-dialects" revision="2"> - <title>Hibernate SQL Dialects (<literal>hibernate.dialect</literal>)</title> - <tgroup cols="2"> -<!-- - <colspec colwidth="1*"/> - <colspec colwidth="2.5*"/> ---> - <thead> - <row> - <entry>RDBMS</entry> - <entry>Dialect</entry> - </row> - </thead> - <tbody> - <row> - <entry>DB2</entry> <entry><literal>org.hibernate.dialect.DB2Dialect</literal></entry> - </row> - <row> - <entry>DB2 AS/400</entry> <entry><literal>org.hibernate.dialect.DB2400Dialect</literal></entry> - </row> - <row> - <entry>DB2 OS390</entry> <entry><literal>org.hibernate.dialect.DB2390Dialect</literal></entry> - </row> - <row> - <entry>PostgreSQL</entry> <entry><literal>org.hibernate.dialect.PostgreSQLDialect</literal></entry> - </row> - <row> - <entry>MySQL</entry> <entry><literal>org.hibernate.dialect.MySQLDialect</literal></entry> - </row> - <row> - <entry>MySQL with InnoDB</entry> <entry><literal>org.hibernate.dialect.MySQLInnoDBDialect</literal></entry> - </row> - <row> - <entry>MySQL with MyISAM</entry> <entry><literal>org.hibernate.dialect.MySQLMyISAMDialect</literal></entry> - </row> - <row> - <entry>Oracle (any version)</entry> <entry><literal>org.hibernate.dialect.OracleDialect</literal></entry> - </row> - <row> - <entry>Oracle 9i/10g</entry> <entry><literal>org.hibernate.dialect.Oracle9Dialect</literal></entry> - </row> - <row> - <entry>Sybase</entry> <entry><literal>org.hibernate.dialect.SybaseDialect</literal></entry> - </row> - <row> - <entry>Sybase Anywhere</entry> <entry><literal>org.hibernate.dialect.SybaseAnywhereDialect</literal></entry> - </row> - <row> - <entry>Microsoft SQL Server</entry> <entry><literal>org.hibernate.dialect.SQLServerDialect</literal></entry> - </row> - <row> - <entry>SAP DB</entry> <entry><literal>org.hibernate.dialect.SAPDBDialect</literal></entry> - </row> - <row> - <entry>Informix</entry> <entry><literal>org.hibernate.dialect.InformixDialect</literal></entry> - </row> - <row> - <entry>HypersonicSQL</entry> <entry><literal>org.hibernate.dialect.HSQLDialect</literal></entry> - </row> - <row> - <entry>Ingres</entry> <entry><literal>org.hibernate.dialect.IngresDialect</literal></entry> - </row> - <row> - <entry>Progress</entry> <entry><literal>org.hibernate.dialect.ProgressDialect</literal></entry> - </row> - <row> - <entry>Mckoi SQL</entry> <entry><literal>org.hibernate.dialect.MckoiDialect</literal></entry> - </row> - <row> - <entry>Interbase</entry> <entry><literal>org.hibernate.dialect.InterbaseDialect</literal></entry> - </row> - <row> - <entry>Pointbase</entry> <entry><literal>org.hibernate.dialect.PointbaseDialect</literal></entry> - </row> - <row> - <entry>FrontBase</entry> <entry><literal>org.hibernate.dialect.FrontbaseDialect</literal></entry> - </row> - <row> - <entry>Firebird</entry> <entry><literal>org.hibernate.dialect.FirebirdDialect</literal></entry> - </row> - </tbody> - </tgroup> - </table> - - </sect2> - - <sect2 id="configuration-optional-outerjoin" revision="4"> - <title>Outer Join Fetching</title> - - <para> - If your database supports ANSI, Oracle or Sybase style outer joins, <emphasis>outer join - fetching</emphasis> will often increase performance by limiting the number of round - trips to and from the database (at the cost of possibly more work performed by - the database itself). Outer join fetching allows a whole graph of objects connected - by many-to-one, one-to-many, many-to-many and one-to-one associations to be retrieved - in a single SQL <literal>SELECT</literal>. - </para> - - <para> - Outer join fetching may be disabled <emphasis>globally</emphasis> by setting - the property <literal>hibernate.max_fetch_depth</literal> to <literal>0</literal>. - A setting of <literal>1</literal> or higher enables outer join fetching for - one-to-one and many-to-one associations which have been mapped with - <literal>fetch="join"</literal>. - </para> - - <para> - See <xref linkend="performance-fetching"/> for more information. - </para> - - </sect2> - - <sect2 id="configuration-optional-binarystreams" revision="1"> - <title>Binary Streams</title> - - <para> - Oracle limits the size of <literal>byte</literal> arrays that may - be passed to/from its JDBC driver. If you wish to use large instances of - <literal>binary</literal> or <literal>serializable</literal> type, you should - enable <literal>hibernate.jdbc.use_streams_for_binary</literal>. - <emphasis>This is a system-level setting only.</emphasis> - </para> - - </sect2> - - <sect2 id="configuration-optional-cacheprovider" revision="2"> - <title>Second-level and query cache</title> - - <para> - The properties prefixed by <literal>hibernate.cache</literal> - allow you to use a process or cluster scoped second-level cache system - with Hibernate. See the <xref linkend="performance-cache"/> for - more details. - </para> - - </sect2> - - <sect2 id="configuration-optional-querysubstitution"> - <title>Query Language Substitution</title> - - <para> - You may define new Hibernate query tokens using <literal>hibernate.query.substitutions</literal>. - For example: - </para> - - <programlisting>hibernate.query.substitutions true=1, false=0</programlisting> - - <para> - would cause the tokens <literal>true</literal> and <literal>false</literal> to be translated to - integer literals in the generated SQL. - </para> - - <programlisting>hibernate.query.substitutions toLowercase=LOWER</programlisting> - - <para> - would allow you to rename the SQL <literal>LOWER</literal> function. - </para> - - </sect2> - - <sect2 id="configuration-optional-statistics" revision="2"> - <title>Hibernate statistics</title> - - <para> - If you enable <literal>hibernate.generate_statistics</literal>, Hibernate will - expose a number of metrics that are useful when tuning a running system via - <literal>SessionFactory.getStatistics()</literal>. Hibernate can even be configured - to expose these statistics via JMX. Read the Javadoc of the interfaces in - <literal>org.hibernate.stats</literal> for more information. - </para> - - </sect2> - </sect1> - - <sect1 id="configuration-logging"> - <title>Logging</title> - - <para> - Hibernate utilizes <ulink url="http://www.slf4j.org/">Simple Logging Facade for Java</ulink> - (SLF4J) in order to log various system events. SLF4J can direct your logging output to - several logging frameworks (NOP, Simple, log4j version 1.2, JDK 1.4 logging, JCL or logback) depending on your - chosen binding. In order to setup logging properly you will need <filename>slf4j-api.jar</filename> in - your classpath together with the jar file for your preferred binding - <filename>slf4j-log4j12.jar</filename> - in the case of Log4J. See the SLF4J <ulink url="http://www.slf4j.org/manual.html">documentation</uli... for more detail. - To use Log4j you will also need to place a <filename>log4j.properties</filename> file in your classpath, - an example properties file is distributed with Hibernate in the <literal>src/</literal> directory. - </para> - - <para> - We strongly recommend that you familiarize yourself with Hibernate's log - messages. A lot of work has been put into making the Hibernate log as - detailed as possible, without making it unreadable. It is an essential - troubleshooting device. The most interesting log categories are the - following: - </para> - - <table frame="topbot" id="log-categories" revision="2"> - <title>Hibernate Log Categories</title> - <tgroup cols="2"> - <colspec colwidth="1*"/> - <colspec colwidth="2.5*"/> - <thead> - <row> - <entry>Category</entry> - <entry>Function</entry> - </row> - </thead> - <tbody> - <row> - <entry><literal>org.hibernate.SQL</literal></entry> - <entry>Log all SQL DML statements as they are executed</entry> - </row> - <row> - <entry><literal>org.hibernate.type</literal></entry> - <entry>Log all JDBC parameters</entry> - </row> - <row> - <entry><literal>org.hibernate.tool.hbm2ddl</literal></entry> - <entry>Log all SQL DDL statements as they are executed</entry> - </row> - <row> - <entry><literal>org.hibernate.pretty</literal></entry> - <entry> - Log the state of all entities (max 20 entities) associated - with the session at flush time - </entry> - </row> - <row> - <entry><literal>org.hibernate.cache</literal></entry> - <entry>Log all second-level cache activity</entry> - </row> - <row> - <entry><literal>org.hibernate.transaction</literal></entry> - <entry>Log transaction related activity</entry> - </row> - <row> - <entry><literal>org.hibernate.jdbc</literal></entry> - <entry>Log all JDBC resource acquisition</entry> - </row> - <row> - <entry><literal>org.hibernate.hql.ast.AST</literal></entry> - <entry> - Log HQL and SQL ASTs during query parsing - </entry> - </row> - <row> - <entry><literal>org.hibernate.secure</literal></entry> - <entry>Log all JAAS authorization requests</entry> - </row> - <row> - <entry><literal>org.hibernate</literal></entry> - <entry> - Log everything (a lot of information, but very useful for - troubleshooting) - </entry> - </row> - </tbody> - </tgroup> - </table> - - <para> - When developing applications with Hibernate, you should almost always work with - <literal>debug</literal> enabled for the category <literal>org.hibernate.SQL</literal>, - or, alternatively, the property <literal>hibernate.show_sql</literal> enabled. - </para> - - - </sect1> - - <sect1 id="configuration-namingstrategy"> - <title>Implementing a <literal>NamingStrategy</literal></title> - - <para> - The interface <literal>org.hibernate.cfg.NamingStrategy</literal> allows you - to specify a "naming standard" for database objects and schema elements. - </para> - - <para> - You may provide rules for automatically generating database identifiers from - Java identifiers or for processing "logical" column and table names given in - the mapping file into "physical" table and column names. This feature helps - reduce the verbosity of the mapping document, eliminating repetitive noise - (<literal>TBL_</literal> prefixes, for example). The default strategy used by - Hibernate is quite minimal. - </para> - - <para> - You may specify a different strategy by calling - <literal>Configuration.setNamingStrategy()</literal> before adding mappings: - </para> - - <programlisting><![CDATA[SessionFactory sf = new Configuration() - .setNamingStrategy(ImprovedNamingStrategy.INSTANCE) - .addFile("Item.hbm.xml") - .addFile("Bid.hbm.xml") - .buildSessionFactory();]]></programlisting> - - <para> - <literal>org.hibernate.cfg.ImprovedNamingStrategy</literal> is a built-in - strategy that might be a useful starting point for some applications. - </para> - - </sect1> - - <sect1 id="configuration-xmlconfig" revision="2"> - <title>XML configuration file</title> - - <para> - An alternative approach to configuration is to specify a full configuration in - a file named <literal>hibernate.cfg.xml</literal>. This file can be used as a - replacement for the <literal>hibernate.properties</literal> file or, if both - are present, to override properties. - </para> - - <para> - The XML configuration file is by default expected to be in the root o - your <literal>CLASSPATH</literal>. Here is an example: - </para> - - <programlisting><![CDATA[<?xml version='1.0' encoding='utf-8'?> -<!DOCTYPE hibernate-configuration PUBLIC - "-//Hibernate/Hibernate Configuration DTD//EN" - "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd"> - -<hibernate-configuration> - - <!-- a SessionFactory instance listed as /jndi/name --> - <session-factory - name="java:hibernate/SessionFactory"> - - <!-- properties --> - <property name="connection.datasource">java:/comp/env/jdbc/MyDB</property> - <property name="dialect">org.hibernate.dialect.MySQLDialect</property> - <property name="show_sql">false</property> - <property name="transaction.factory_class"> - org.hibernate.transaction.JTATransactionFactory - </property> - <property name="jta.UserTransaction">java:comp/UserTransaction</property> - - <!-- mapping files --> - <mapping resource="org/hibernate/auction/Item.hbm.xml"/> - <mapping resource="org/hibernate/auction/Bid.hbm.xml"/> - - <!-- cache settings --> - <class-cache class="org.hibernate.auction.Item" usage="read-write"/> - <class-cache class="org.hibernate.auction.Bid" usage="read-only"/> - <collection-cache collection="org.hibernate.auction.Item.bids" usage="read-write"/> - - </session-factory> - -</hibernate-configuration>]]></programlisting> - - <para> - As you can see, the advantage of this approach is the externalization of the - mapping file names to configuration. The <literal>hibernate.cfg.xml</literal> - is also more convenient once you have to tune the Hibernate cache. Note that is - your choice to use either <literal>hibernate.properties</literal> or - <literal>hibernate.cfg.xml</literal>, both are equivalent, except for the above - mentioned benefits of using the XML syntax. - </para> - - <para> - With the XML configuration, starting Hibernate is then as simple as - </para> - - <programlisting><![CDATA[SessionFactory sf = new Configuration().configure().buildSessionFactory();]]></programlisting> - - <para> - You can pick a different XML configuration file using - </para> - - <programlisting><![CDATA[SessionFactory sf = new Configuration() - .configure("catdb.cfg.xml") - .buildSessionFactory();]]></programlisting> - - </sect1> - - <sect1 id="configuration-j2ee" revision="1"> - <title>J2EE Application Server integration</title> - - <para> - Hibernate has the following integration points for J2EE infrastructure: - </para> - - <itemizedlist> - <listitem> - <para> - <emphasis>Container-managed datasources</emphasis>: Hibernate can use - JDBC connections managed by the container and provided through JNDI. Usually, - a JTA compatible <literal>TransactionManager</literal> and a - <literal>ResourceManager</literal> take care of transaction management (CMT), - esp. distributed transaction handling across several datasources. You may - of course also demarcate transaction boundaries programmatically (BMT) or - you might want to use the optional Hibernate <literal>Transaction</literal> - API for this to keep your code portable. - </para> - </listitem> - </itemizedlist> - - <itemizedlist> - <listitem> - <para> - <emphasis>Automatic JNDI binding</emphasis>: Hibernate can bind its - <literal>SessionFactory</literal> to JNDI after startup. - </para> - </listitem> - </itemizedlist> - - <itemizedlist> - <listitem> - <para> - <emphasis>JTA Session binding:</emphasis> The Hibernate <literal>Session</literal> - may be automatically bound to the scope of JTA transactions. Simply - lookup the <literal>SessionFactory</literal> from JNDI and get the current - <literal>Session</literal>. Let Hibernate take care of flushing and closing the - <literal>Session</literal> when your JTA transaction completes. Transaction - demarcation is either declarative (CMT) or programmatic (BMT/UserTransaction). - </para> - </listitem> - </itemizedlist> - - <itemizedlist> - <listitem> - <para> - <emphasis>JMX deployment:</emphasis> If you have a JMX capable application server - (e.g. JBoss AS), you can chose to deploy Hibernate as a managed MBean. This saves - you the one line startup code to build your <literal>SessionFactory</literal> from - a <literal>Configuration</literal>. The container will startup your - <literal>HibernateService</literal>, and ideally also take care of service - dependencies (Datasource has to be available before Hibernate starts, etc). - </para> - </listitem> - </itemizedlist> - - <para> - Depending on your environment, you might have to set the configuration option - <literal>hibernate.connection.aggressive_release</literal> to true if your - application server shows "connection containment" exceptions. - </para> - - <sect2 id="configuration-optional-transactionstrategy" revision="3"> - <title>Transaction strategy configuration</title> - - <para> - The Hibernate <literal>Session</literal> API is independent of any transaction - demarcation system in your architecture. If you let Hibernate use JDBC directly, - through a connection pool, you may begin and end your transactions by calling - the JDBC API. If you run in a J2EE application server, you might want to use bean-managed - transactions and call the JTA API and <literal>UserTransaction</literal> when needed. - </para> - - <para> - To keep your code portable between these two (and other) environments we recommend the optional - Hibernate <literal>Transaction</literal> API, which wraps and hides the underlying system. - You have to specify a factory class for <literal>Transaction</literal> instances by setting the - Hibernate configuration property <literal>hibernate.transaction.factory_class</literal>. - </para> - - <para> - There are three standard (built-in) choices: - </para> - - <variablelist spacing="compact"> - <varlistentry> - <term><literal>org.hibernate.transaction.JDBCTransactionFactory</literal></term> - <listitem> - <para>delegates to database (JDBC) transactions (default)</para> - </listitem> - </varlistentry> - <varlistentry> - <term><literal>org.hibernate.transaction.JTATransactionFactory</literal></term> - <listitem> - <para> - delegates to container-managed transaction if an existing transaction is - underway in this context (e.g. EJB session bean method), otherwise - a new transaction is started and bean-managed transaction are used. - </para> - </listitem> - </varlistentry> - <varlistentry> - <term><literal>org.hibernate.transaction.CMTTransactionFactory</literal></term> - <listitem> - <para>delegates to container-managed JTA transactions</para> - </listitem> - </varlistentry> - </variablelist> - - <para> - You may also define your own transaction strategies (for a CORBA transaction service, - for example). - </para> - - <para> - Some features in Hibernate (i.e. the second level cache, Contextual Sessions with JTA, etc.) - require access to the JTA <literal>TransactionManager</literal> in a managed environment. - In an application server you have to specify how Hibernate should obtain a reference to the - <literal>TransactionManager</literal>, since J2EE does not standardize a single mechanism: - </para> - - <table frame="topbot" id="jtamanagerlookup" revision="1"> - <title>JTA TransactionManagers</title> - <tgroup cols="2"> - <colspec colwidth="2.5*"/> - <colspec colwidth="1*"/> - <thead> - <row> - <entry>Transaction Factory</entry> - <entry align="center">Application Server</entry> - </row> - </thead> - <tbody> - <row> - <entry><literal>org.hibernate.transaction.JBossTransactionManagerLookup</literal></entry> - <entry align="center">JBoss</entry> - </row> - <row> - <entry><literal>org.hibernate.transaction.WeblogicTransactionManagerLookup</literal></entry> - <entry align="center">Weblogic</entry> - </row> - <row> - <entry><literal>org.hibernate.transaction.WebSphereTransactionManagerLookup</literal></entry> - <entry align="center">WebSphere</entry> - </row> - <row> - <entry><literal>org.hibernate.transaction.WebSphereExtendedJTATransactionLookup</literal></entry> - <entry align="center">WebSphere 6</entry> - </row> - <row> - <entry><literal>org.hibernate.transaction.OrionTransactionManagerLookup</literal></entry> - <entry align="center">Orion</entry> - </row> - <row> - <entry><literal>org.hibernate.transaction.ResinTransactionManagerLookup</literal></entry> - <entry align="center">Resin</entry> - </row> - <row> - <entry><literal>org.hibernate.transaction.JOTMTransactionManagerLookup</literal></entry> - <entry align="center">JOTM</entry> - </row> - <row> - <entry><literal>org.hibernate.transaction.JOnASTransactionManagerLookup</literal></entry> - <entry align="center">JOnAS</entry> - </row> - <row> - <entry><literal>org.hibernate.transaction.JRun4TransactionManagerLookup</literal></entry> - <entry align="center">JRun4</entry> - </row> - <row> - <entry><literal>org.hibernate.transaction.BESTransactionManagerLookup</literal></entry> - <entry align="center">Borland ES</entry> - </row> - </tbody> - </tgroup> - </table> - - </sect2> - - <sect2 id="configuration-optional-jndi" revision="3"> - <title>JNDI-bound <literal>SessionFactory</literal></title> - - <para> - A JNDI bound Hibernate <literal>SessionFactory</literal> can simplify the lookup - of the factory and the creation of new <literal>Session</literal>s. Note that this - is not related to a JNDI bound <literal>Datasource</literal>, both simply use the - same registry! - </para> - - <para> - If you wish to have the <literal>SessionFactory</literal> bound to a JNDI namespace, specify - a name (eg. <literal>java:hibernate/SessionFactory</literal>) using the property - <literal>hibernate.session_factory_name</literal>. If this property is omitted, the - <literal>SessionFactory</literal> will not be bound to JNDI. (This is especially useful in - environments with a read-only JNDI default implementation, e.g. Tomcat.) - </para> - - <para> - When binding the <literal>SessionFactory</literal> to JNDI, Hibernate will use the values of - <literal>hibernate.jndi.url</literal>, <literal>hibernate.jndi.class</literal> to instantiate - an initial context. If they are not specified, the default <literal>InitialContext</literal> - will be used. - </para> - - <para> - Hibernate will automatically place the <literal>SessionFactory</literal> in JNDI after - you call <literal>cfg.buildSessionFactory()</literal>. This means you will at least have - this call in some startup code (or utility class) in your application, unless you use - JMX deployment with the <literal>HibernateService</literal> (discussed later). - </para> - - <para> - If you use a JNDI <literal>SessionFactory</literal>, an EJB or any other class may - obtain the <literal>SessionFactory</literal> using a JNDI lookup. - </para> - - <para> - We recommend that you bind the <literal>SessionFactory</literal> to JNDI in - a managed environment and use a <literal>static</literal> singleton otherwise. - To shield your application code from these details, we also recommend to hide the - actual lookup code for a <literal>SessionFactory</literal> in a helper class, - such as <literal>HibernateUtil.getSessionFactory()</literal>. Note that such a - class is also a convenient way to startup Hibernate&mdash;see chapter 1. - </para> - - </sect2> - - <sect2 id="configuration-j2ee-currentsession" revision="4"> - <title>Current Session context management with JTA</title> - - <para> - The easiest way to handle <literal>Session</literal>s and transactions is - Hibernates automatic "current" <literal>Session</literal> management. - See the discussion of <link linkend="architecture-current-session">current sessions</link>. - Using the <literal>"jta"</literal> session context, if there is no Hibernate - <literal>Session</literal> associated with the current JTA transaction, one will - be started and associated with that JTA transaction the first time you call - <literal>sessionFactory.getCurrentSession()</literal>. The <literal>Session</literal>s - retrieved via <literal>getCurrentSession()</literal> in <literal>"jta"</literal> context - will be set to automatically flush before the transaction completes, close - after the transaction completes, and aggressively release JDBC connections - after each statement. This allows the <literal>Session</literal>s to - be managed by the life cycle of the JTA transaction to which it is associated, - keeping user code clean of such management concerns. Your code can either use - JTA programmatically through <literal>UserTransaction</literal>, or (recommended - for portable code) use the Hibernate <literal>Transaction</literal> API to set - transaction boundaries. If you run in an EJB container, declarative transaction - demarcation with CMT is preferred. - </para> - - </sect2> - - <sect2 id="configuration-j2ee-jmx" revision="1"> - <title>JMX deployment</title> - - <para> - The line <literal>cfg.buildSessionFactory()</literal> still has to be executed - somewhere to get a <literal>SessionFactory</literal> into JNDI. You can do this - either in a <literal>static</literal> initializer block (like the one in - <literal>HibernateUtil</literal>) or you deploy Hibernate as a <emphasis>managed - service</emphasis>. - </para> - - <para> - Hibernate is distributed with <literal>org.hibernate.jmx.HibernateService</literal> - for deployment on an application server with JMX capabilities, such as JBoss AS. - The actual deployment and configuration is vendor specific. Here is an example - <literal>jboss-service.xml</literal> for JBoss 4.0.x: - </para> - - <programlisting><![CDATA[<?xml version="1.0"?> -<server> - -<mbean code="org.hibernate.jmx.HibernateService" - name="jboss.jca:service=HibernateFactory,name=HibernateFactory"> - - <!-- Required services --> - <depends>jboss.jca:service=RARDeployer</depends> - <depends>jboss.jca:service=LocalTxCM,name=HsqlDS</depends> - - <!-- Bind the Hibernate service to JNDI --> - <attribute name="JndiName">java:/hibernate/SessionFactory</attribute> - - <!-- Datasource settings --> - <attribute name="Datasource">java:HsqlDS</attribute> - <attribute name="Dialect">org.hibernate.dialect.HSQLDialect</attribute> - - <!-- Transaction integration --> - <attribute name="TransactionStrategy"> - org.hibernate.transaction.JTATransactionFactory</attribute> - <attribute name="TransactionManagerLookupStrategy"> - org.hibernate.transaction.JBossTransactionManagerLookup</attribute> - <attribute name="FlushBeforeCompletionEnabled">true</attribute> - <attribute name="AutoCloseSessionEnabled">true</attribute> - - <!-- Fetching options --> - <attribute name="MaximumFetchDepth">5</attribute> - - <!-- Second-level caching --> - <attribute name="SecondLevelCacheEnabled">true</attribute> - <attribute name="CacheProviderClass">org.hibernate.cache.EhCacheProvider</attribute> - <attribute name="QueryCacheEnabled">true</attribute> - - <!-- Logging --> - <attribute name="ShowSqlEnabled">true</attribute> - - <!-- Mapping files --> - <attribute name="MapResources">auction/Item.hbm.xml,auction/Category.hbm.xml</attribute> - -</mbean> - -</server>]]></programlisting> - - <para> - This file is deployed in a directory called <literal>META-INF</literal> and packaged - in a JAR file with the extension <literal>.sar</literal> (service archive). You also need - to package Hibernate, its required third-party libraries, your compiled persistent classes, - as well as your mapping files in the same archive. Your enterprise beans (usually session - beans) may be kept in their own JAR file, but you may include this EJB JAR file in the - main service archive to get a single (hot-)deployable unit. Consult the JBoss AS - documentation for more information about JMX service and EJB deployment. - </para> - - </sect2> - - </sect1> - -</chapter> - Deleted: core/trunk/documentation/envers/src/main/docbook/en-US/content/events.xml =================================================================== --- core/trunk/documentation/envers/src/main/docbook/en-US/content/events.xml 2008-11-04 17:31:01 UTC (rev 15499) +++ core/trunk/documentation/envers/src/main/docbook/en-US/content/events.xml 2008-11-04 17:31:43 UTC (rev 15500) @@ -1,292 +0,0 @@ -<?xml version='1.0' encoding="UTF-8"?> -<!-- - ~ Hibernate, Relational Persistence for Idiomatic Java - ~ - ~ Copyright (c) 2008, Red Hat Middleware LLC or third-party contributors as - ~ indicated by the @author tags or express copyright attribution - ~ statements applied by the authors. All third-party contributions are - ~ distributed under license by Red Hat Middleware LLC. - ~ - ~ This copyrighted material is made available to anyone wishing to use, modify, - ~ copy, or redistribute it subject to the terms and conditions of the GNU - ~ Lesser General Public License, as published by the Free Software Foundation. - ~ - ~ This program is distributed in the hope that it will be useful, - ~ but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY - ~ or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License - ~ for more details. - ~ - ~ You should have received a copy of the GNU Lesser General Public License - ~ along with this distribution; if not, write to: - ~ Free Software Foundation, Inc. - ~ 51 Franklin Street, Fifth Floor - ~ Boston, MA 02110-1301 USA - --> - -<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd"> - -<chapter id="events"> - <title>Interceptors and events</title> - - <para> - It is often useful for the application to react to certain events that occur - inside Hibernate. This allows implementation of certain kinds of generic - functionality, and extension of Hibernate functionality. - </para> - - <sect1 id="objectstate-interceptors" revision="3"> - <title>Interceptors</title> - - <para> - The <literal>Interceptor</literal> interface provides callbacks from the session to the - application allowing the application to inspect and/or manipulate properties of a - persistent object before it is saved, updated, deleted or loaded. One - possible use for this is to track auditing information. For example, the following - <literal>Interceptor</literal> automatically sets the <literal>createTimestamp</literal> - when an <literal>Auditable</literal> is created and updates the - <literal>lastUpdateTimestamp</literal> property when an <literal>Auditable</literal> is - updated. - </para> - - <para> - You may either implement <literal>Interceptor</literal> directly or (better) extend - <literal>EmptyInterceptor</literal>. - </para> - - <programlisting><![CDATA[package org.hibernate.test; - -import java.io.Serializable; -import java.util.Date; -import java.util.Iterator; - -import org.hibernate.EmptyInterceptor; -import org.hibernate.Transaction; -import org.hibernate.type.Type; - -public class AuditInterceptor extends EmptyInterceptor { - - private int updates; - private int creates; - private int loads; - - public void onDelete(Object entity, - Serializable id, - Object[] state, - String[] propertyNames, - Type[] types) { - // do nothing - } - - public boolean onFlushDirty(Object entity, - Serializable id, - Object[] currentState, - Object[] previousState, - String[] propertyNames, - Type[] types) { - - if ( entity instanceof Auditable ) { - updates++; - for ( int i=0; i < propertyNames.length; i++ ) { - if ( "lastUpdateTimestamp".equals( propertyNames[i] ) ) { - currentState[i] = new Date(); - return true; - } - } - } - return false; - } - - public boolean onLoad(Object entity, - Serializable id, - Object[] state, - String[] propertyNames, - Type[] types) { - if ( entity instanceof Auditable ) { - loads++; - } - return false; - } - - public boolean onSave(Object entity, - Serializable id, - Object[] state, - String[] propertyNames, - Type[] types) { - - if ( entity instanceof Auditable ) { - creates++; - for ( int i=0; i<propertyNames.length; i++ ) { - if ( "createTimestamp".equals( propertyNames[i] ) ) { - state[i] = new Date(); - return true; - } - } - } - return false; - } - - public void afterTransactionCompletion(Transaction tx) { - if ( tx.wasCommitted() ) { - System.out.println("Creations: " + creates + ", Updates: " + updates, "Loads: " + loads); - } - updates=0; - creates=0; - loads=0; - } - -}]]></programlisting> - - <para> - Interceptors come in two flavors: <literal>Session</literal>-scoped and - <literal>SessionFactory</literal>-scoped. - </para> - - <para> - A <literal>Session</literal>-scoped interceptor is specified - when a session is opened using one of the overloaded SessionFactory.openSession() - methods accepting an <literal>Interceptor</literal>. - </para> - - <programlisting><![CDATA[Session session = sf.openSession( new AuditInterceptor() );]]></programlisting> - - <para> - A <literal>SessionFactory</literal>-scoped interceptor is registered with the <literal>Configuration</literal> - object prior to building the <literal>SessionFactory</literal>. In this case, the supplied interceptor - will be applied to all sessions opened from that <literal>SessionFactory</literal>; this is true unless - a session is opened explicitly specifying the interceptor to use. <literal>SessionFactory</literal>-scoped - interceptors must be thread safe, taking care to not store session-specific state since multiple - sessions will use this interceptor (potentially) concurrently. - </para> - - <programlisting><![CDATA[new Configuration().setInterceptor( new AuditInterceptor() );]]></programlisting> - - </sect1> - - <sect1 id="objectstate-events" revision="4"> - <title>Event system</title> - - <para> - If you have to react to particular events in your persistence layer, you may - also use the Hibernate3 <emphasis>event</emphasis> architecture. The event - system can be used in addition or as a replacement for interceptors. - </para> - - <para> - Essentially all of the methods of the <literal>Session</literal> interface correlate - to an event. You have a <literal>LoadEvent</literal>, a <literal>FlushEvent</literal>, etc - (consult the XML configuration-file DTD or the <literal>org.hibernate.event</literal> - package for the full list of defined event types). When a request is made of one of - these methods, the Hibernate <literal>Session</literal> generates an appropriate - event and passes it to the configured event listeners for that type. Out-of-the-box, - these listeners implement the same processing in which those methods always resulted. - However, you are free to implement a customization of one of the listener interfaces - (i.e., the <literal>LoadEvent</literal> is processed by the registered implemenation - of the <literal>LoadEventListener</literal> interface), in which case their - implementation would be responsible for processing any <literal>load()</literal> requests - made of the <literal>Session</literal>. - </para> - - <para> - The listeners should be considered effectively singletons; meaning, they are shared between - requests, and thus should not save any state as instance variables. - </para> - - <para> - A custom listener should implement the appropriate interface for the event it wants to - process and/or extend one of the convenience base classes (or even the default event - listeners used by Hibernate out-of-the-box as these are declared non-final for this - purpose). Custom listeners can either be registered programmatically through the - <literal>Configuration</literal> object, or specified in the Hibernate configuration - XML (declarative configuration through the properties file is not supported). Here's an - example of a custom load event listener: - </para> - - <programlisting><![CDATA[public class MyLoadListener implements LoadEventListener { - // this is the single method defined by the LoadEventListener interface - public void onLoad(LoadEvent event, LoadEventListener.LoadType loadType) - throws HibernateException { - if ( !MySecurity.isAuthorized( event.getEntityClassName(), event.getEntityId() ) ) { - throw MySecurityException("Unauthorized access"); - } - } -}]]></programlisting> - - <para> - You also need a configuration entry telling Hibernate to use the listener in addition - to the default listener: - </para> - -<programlisting><![CDATA[<hibernate-configuration> - <session-factory> - ... - <event type="load"> - <listener class="com.eg.MyLoadListener"/> - <listener class="org.hibernate.event.def.DefaultLoadEventListener"/> - </event> - </session-factory> -</hibernate-configuration>]]></programlisting> - - <para> - Instead, you may register it programmatically: - </para> - - <programlisting><![CDATA[Configuration cfg = new Configuration(); -LoadEventListener[] stack = { new MyLoadListener(), new DefaultLoadEventListener() }; -cfg.EventListeners().setLoadEventListeners(stack);]]></programlisting> - - <para> - Listeners registered declaratively cannot share instances. If the same class name is - used in multiple <literal>&lt;listener/&gt;</literal> elements, each reference will - result in a separate instance of that class. If you need the capability to share - listener instances between listener types you must use the programmatic registration - approach. - </para> - - <para> - Why implement an interface and define the specific type during configuration? Well, a - listener implementation could implement multiple event listener interfaces. Having the - type additionally defined during registration makes it easier to turn custom listeners on - or off during configuration. - </para> - - </sect1> - - <sect1 id="objectstate-decl-security" revision="2"> - <title>Hibernate declarative security</title> - <para> - Usually, declarative security in Hibernate applications is managed in a session facade - layer. Now, Hibernate3 allows certain actions to be permissioned via JACC, and authorized - via JAAS. This is optional functionality built on top of the event architecture. - </para> - - <para> - First, you must configure the appropriate event listeners, to enable the use of JAAS - authorization. - </para> - - <programlisting><![CDATA[<listener type="pre-delete" class="org.hibernate.secure.JACCPreDeleteEventListener"/> -<listener type="pre-update" class="org.hibernate.secure.JACCPreUpdateEventListener"/> -<listener type="pre-insert" class="org.hibernate.secure.JACCPreInsertEventListener"/> -<listener type="pre-load" class="org.hibernate.secure.JACCPreLoadEventListener"/>]]></programlisting> - - <para> - Note that <literal>&lt;listener type="..." class="..."/&gt;</literal> is just a shorthand - for <literal>&lt;event type="..."&gt;&lt;listener class="..."/&gt;&lt;/event&gt;</literal> - when there is exactly one listener for a particular event type. - </para> - - <para> - Next, still in <literal>hibernate.cfg.xml</literal>, bind the permissions to roles: - </para> - - <programlisting><![CDATA[<grant role="admin" entity-name="User" actions="insert,update,read"/> -<grant role="su" entity-name="User" actions="*"/>]]></programlisting> - - <para> - The role names are the roles understood by your JACC provider. - </para> - - </sect1> - -</chapter> - Deleted: core/trunk/documentation/envers/src/main/docbook/en-US/content/example_mappings.xml =================================================================== --- core/trunk/documentation/envers/src/main/docbook/en-US/content/example_mappings.xml 2008-11-04 17:31:01 UTC (rev 15499) +++ core/trunk/documentation/envers/src/main/docbook/en-US/content/example_mappings.xml 2008-11-04 17:31:43 UTC (rev 15500) @@ -1,685 +0,0 @@ -<?xml version='1.0' encoding="UTF-8"?> -<!-- - ~ Hibernate, Relational Persistence for Idiomatic Java - ~ - ~ Copyright (c) 2008, Red Hat Middleware LLC or third-party contributors as - ~ indicated by the @author tags or express copyright attribution - ~ statements applied by the authors. All third-party contributions are - ~ distributed under license by Red Hat Middleware LLC. - ~ - ~ This copyrighted material is made available to anyone wishing to use, modify, - ~ copy, or redistribute it subject to the terms and conditions of the GNU - ~ Lesser General Public License, as published by the Free Software Foundation. - ~ - ~ This program is distributed in the hope that it will be useful, - ~ but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY - ~ or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License - ~ for more details. - ~ - ~ You should have received a copy of the GNU Lesser General Public License - ~ along with this distribution; if not, write to: - ~ Free Software Foundation, Inc. - ~ 51 Franklin Street, Fifth Floor - ~ Boston, MA 02110-1301 USA - --> - -<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd"> - -<chapter id="example-mappings"> - <title>Example: Various Mappings</title> - - <para> - This chapters shows off some more complex association mappings. - </para> - - <sect1 id="example-mappings-emp"> - <title>Employer/Employee</title> - - <para> - The following model of the relationship between <literal>Employer</literal> and - <literal>Employee</literal> uses an actual entity class (<literal>Employment</literal>) - to represent the association. This is done because there might be more than one - period of employment for the same two parties. Components are used to model monetary - values and employee names. - </para> - - <mediaobject> - <imageobject role="html"> - <imagedata fileref="../images/EmployerEmployee.png" format="PNG" align="center" /> - </imageobject> - <imageobject role="fo"> - <imagedata fileref="../images/EmployerEmployee.png" format="PNG" align="center" width="17cm" /> - </imageobject> - </mediaobject> - - <para> - Heres a possible mapping document: - </para> - - <programlisting><![CDATA[<hibernate-mapping> - - <class name="Employer" table="employers"> - <id name="id"> - <generator class="sequence"> - <param name="sequence">employer_id_seq</param> - </generator> - </id> - <property name="name"/> - </class> - - <class name="Employment" table="employment_periods"> - - <id name="id"> - <generator class="sequence"> - <param name="sequence">employment_id_seq</param> - </generator> - </id> - <property name="startDate" column="start_date"/> - <property name="endDate" column="end_date"/> - - <component name="hourlyRate" class="MonetaryAmount"> - <property name="amount"> - <column name="hourly_rate" sql-type="NUMERIC(12, 2)"/> - </property> - <property name="currency" length="12"/> - </component> - - <many-to-one name="employer" column="employer_id" not-null="true"/> - <many-to-one name="employee" column="employee_id" not-null="true"/> - - </class> - - <class name="Employee" table="employees"> - <id name="id"> - <generator class="sequence"> - <param name="sequence">employee_id_seq</param> - </generator> - </id> - <property name="taxfileNumber"/> - <component name="name" class="Name"> - <property name="firstName"/> - <property name="initial"/> - <property name="lastName"/> - </component> - </class> - -</hibernate-mapping>]]></programlisting> - - <para> - And heres the table schema generated by <literal>SchemaExport</literal>. - </para> - - <programlisting><![CDATA[create table employers ( - id BIGINT not null, - name VARCHAR(255), - primary key (id) -) - -create table employment_periods ( - id BIGINT not null, - hourly_rate NUMERIC(12, 2), - currency VARCHAR(12), - employee_id BIGINT not null, - employer_id BIGINT not null, - end_date TIMESTAMP, - start_date TIMESTAMP, - primary key (id) -) - -create table employees ( - id BIGINT not null, - firstName VARCHAR(255), - initial CHAR(1), - lastName VARCHAR(255), - taxfileNumber VARCHAR(255), - primary key (id) -) - -alter table employment_periods - add constraint employment_periodsFK0 foreign key (employer_id) references employers -alter table employment_periods - add constraint employment_periodsFK1 foreign key (employee_id) references employees -create sequence employee_id_seq -create sequence employment_id_seq -create sequence employer_id_seq]]></programlisting> - - </sect1> - - <sect1 id="example-mappings-authorwork"> - <title>Author/Work</title> - - <para> - Consider the following model of the relationships between <literal>Work</literal>, - <literal>Author</literal> and <literal>Person</literal>. We represent the relationship - between <literal>Work</literal> and <literal>Author</literal> as a many-to-many - association. We choose to represent the relationship between <literal>Author</literal> - and <literal>Person</literal> as one-to-one association. Another possibility would be to - have <literal>Author</literal> extend <literal>Person</literal>. - </para> - - <mediaobject> - <imageobject role="html"> - <imagedata fileref="../images/AuthorWork.png" format="PNG" align="center" /> - </imageobject> - <imageobject role="fo"> - <imagedata fileref="../images/AuthorWork.png" format="PNG" align="center" width="17cm" /> - </imageobject> - </mediaobject> - - <para> - The following mapping document correctly represents these relationships: - </para> - - <programlisting><![CDATA[<hibernate-mapping> - - <class name="Work" table="works" discriminator-value="W"> - - <id name="id" column="id"> - <generator class="native"/> - </id> - <discriminator column="type" type="character"/> - - <property name="title"/> - <set name="authors" table="author_work"> - <key column name="work_id"/> - <many-to-many class="Author" column name="author_id"/> - </set> - - <subclass name="Book" discriminator-value="B"> - <property name="text"/> - </subclass> - - <subclass name="Song" discriminator-value="S"> - <property name="tempo"/> - <property name="genre"/> - </subclass> - - </class> - - <class name="Author" table="authors"> - - <id name="id" column="id"> - <!-- The Author must have the same identifier as the Person --> - <generator class="assigned"/> - </id> - - <property name="alias"/> - <one-to-one name="person" constrained="true"/> - - <set name="works" table="author_work" inverse="true"> - <key column="author_id"/> - <many-to-many class="Work" column="work_id"/> - </set> - - </class> - - <class name="Person" table="persons"> - <id name="id" column="id"> - <generator class="native"/> - </id> - <property name="name"/> - </class> - -</hibernate-mapping>]]></programlisting> - - <para> - There are four tables in this mapping. <literal>works</literal>, - <literal>authors</literal> and <literal>persons</literal> hold work, author - and person data respectively. <literal>author_work</literal> is an association - table linking authors to works. Heres the table schema, as generated by - <literal>SchemaExport</literal>. - </para> - - <programlisting><![CDATA[create table works ( - id BIGINT not null generated by default as identity, - tempo FLOAT, - genre VARCHAR(255), - text INTEGER, - title VARCHAR(255), - type CHAR(1) not null, - primary key (id) -) - -create table author_work ( - author_id BIGINT not null, - work_id BIGINT not null, - primary key (work_id, author_id) -) - -create table authors ( - id BIGINT not null generated by default as identity, - alias VARCHAR(255), - primary key (id) -) - -create table persons ( - id BIGINT not null generated by default as identity, - name VARCHAR(255), - primary key (id) -) - -alter table authors - add constraint authorsFK0 foreign key (id) references persons -alter table author_work - add constraint author_workFK0 foreign key (author_id) references authors -alter table author_work - add constraint author_workFK1 foreign key (work_id) references works]]></programlisting> - - </sect1> - - <sect1 id="example-mappings-customerorderproduct"> - <title>Customer/Order/Product</title> - - <para> - Now consider a model of the relationships between <literal>Customer</literal>, - <literal>Order</literal> and <literal>LineItem</literal> and <literal>Product</literal>. - There is a one-to-many association between <literal>Customer</literal> and - <literal>Order</literal>, but how should we represent <literal>Order</literal> / - <literal>LineItem</literal> / <literal>Product</literal>? I've chosen to map - <literal>LineItem</literal> as an association class representing the many-to-many - association between <literal>Order</literal> and <literal>Product</literal>. In - Hibernate, this is called a composite element. - </para> - - <mediaobject> - <imageobject role="html"> - <imagedata fileref="../images/CustomerOrderProduct.png" format="PNG" align="center" /> - </imageobject> - <imageobject role="fo"> - <imagedata fileref="../images/CustomerOrderProduct.png" format="PNG" align="center" width="17cm" /> - </imageobject> - </mediaobject> - - <para> - The mapping document: - </para> - - <programlisting><![CDATA[<hibernate-mapping> - - <class name="Customer" table="customers"> - <id name="id"> - <generator class="native"/> - </id> - <property name="name"/> - <set name="orders" inverse="true"> - <key column="customer_id"/> - <one-to-many class="Order"/> - </set> - </class> - - <class name="Order" table="orders"> - <id name="id"> - <generator class="native"/> - </id> - <property name="date"/> - <many-to-one name="customer" column="customer_id"/> - <list name="lineItems" table="line_items"> - <key column="order_id"/> - <list-index column="line_number"/> - <composite-element class="LineItem"> - <property name="quantity"/> - <many-to-one name="product" column="product_id"/> - </composite-element> - </list> - </class> - - <class name="Product" table="products"> - <id name="id"> - <generator class="native"/> - </id> - <property name="serialNumber"/> - </class> - -</hibernate-mapping>]]></programlisting> - - <para> - <literal>customers</literal>, <literal>orders</literal>, <literal>line_items</literal> and - <literal>products</literal> hold customer, order, order line item and product data - respectively. <literal>line_items</literal> also acts as an association table linking - orders with products. - </para> - - <programlisting><![CDATA[create table customers ( - id BIGINT not null generated by default as identity, - name VARCHAR(255), - primary key (id) -) - -create table orders ( - id BIGINT not null generated by default as identity, - customer_id BIGINT, - date TIMESTAMP, - primary key (id) -) - -create table line_items ( - line_number INTEGER not null, - order_id BIGINT not null, - product_id BIGINT, - quantity INTEGER, - primary key (order_id, line_number) -) - -create table products ( - id BIGINT not null generated by default as identity, - serialNumber VARCHAR(255), - primary key (id) -) - -alter table orders - add constraint ordersFK0 foreign key (customer_id) references customers -alter table line_items - add constraint line_itemsFK0 foreign key (product_id) references products -alter table line_items - add constraint line_itemsFK1 foreign key (order_id) references orders]]></programlisting> - - </sect1> - - <sect1 id="misc"> - <title>Miscellaneous example mappings</title> - - <para> - These examples are all taken from the Hibernate test suite. You - will find many other useful example mappings there. Look in the - <literal>test</literal> folder of the Hibernate distribution. - </para> - - <para>TODO: put words around this stuff</para> - - <sect2 id="example-mappings-typed-onetone"> - <title>"Typed" one-to-one association</title> -<programlisting><![CDATA[<class name="Person"> - <id name="name"/> - <one-to-one name="address" - cascade="all"> - <formula>name</formula> - <formula>'HOME'</formula> - </one-to-one> - <one-to-one name="mailingAddress" - cascade="all"> - <formula>name</formula> - <formula>'MAILING'</formula> - </one-to-one> -</class> - -<class name="Address" batch-size="2" - check="addressType in ('MAILING', 'HOME', 'BUSINESS')"> - <composite-id> - <key-many-to-one name="person" - column="personName"/> - <key-property name="type" - column="addressType"/> - </composite-id> - <property name="street" type="text"/> - <property name="state"/> - <property name="zip"/> -</class>]]></programlisting> - </sect2> - - <sect2 id="example-mappings-composite-key"> - <title>Composite key example</title> -<programlisting><![CDATA[<class name="Customer"> - - <id name="customerId" - length="10"> - <generator class="assigned"/> - </id> - - <property name="name" not-null="true" length="100"/> - <property name="address" not-null="true" length="200"/> - - <list name="orders" - inverse="true" - cascade="save-update"> - <key column="customerId"/> - <index column="orderNumber"/> - <one-to-many class="Order"/> - </list> - -</class> - -<class name="Order" table="CustomerOrder" lazy="true"> - <synchronize table="LineItem"/> - <synchronize table="Product"/> - - <composite-id name="id" - class="Order$Id"> - <key-property name="customerId" length="10"/> - <key-property name="orderNumber"/> - </composite-id> - - <property name="orderDate" - type="calendar_date" - not-null="true"/> - - <property name="total"> - <formula> - ( select sum(li.quantity*p.price) - from LineItem li, Product p - where li.productId = p.productId - and li.customerId = customerId - and li.orderNumber = orderNumber ) - </formula> - </property> - - <many-to-one name="customer" - column="customerId" - insert="false" - update="false" - not-null="true"/> - - <bag name="lineItems" - fetch="join" - inverse="true" - cascade="save-update"> - <key> - <column name="customerId"/> - <column name="orderNumber"/> - </key> - <one-to-many class="LineItem"/> - </bag> - -</class> - -<class name="LineItem"> - - <composite-id name="id" - class="LineItem$Id"> - <key-property name="customerId" length="10"/> - <key-property name="orderNumber"/> - <key-property name="productId" length="10"/> - </composite-id> - - <property name="quantity"/> - - <many-to-one name="order" - insert="false" - update="false" - not-null="true"> - <column name="customerId"/> - <column name="orderNumber"/> - </many-to-one> - - <many-to-one name="product" - insert="false" - update="false" - not-null="true" - column="productId"/> - -</class> - -<class name="Product"> - <synchronize table="LineItem"/> - - <id name="productId" - length="10"> - <generator class="assigned"/> - </id> - - <property name="description" - not-null="true" - length="200"/> - <property name="price" length="3"/> - <property name="numberAvailable"/> - - <property name="numberOrdered"> - <formula> - ( select sum(li.quantity) - from LineItem li - where li.productId = productId ) - </formula> - </property> - -</class>]]></programlisting> - </sect2> - - <sect2 id="example-mappings-composite-key-manytomany"> - <title>Many-to-many with shared composite key attribute</title> -<programlisting><![CDATA[<class name="User" table="`User`"> - <composite-id> - <key-property name="name"/> - <key-property name="org"/> - </composite-id> - <set name="groups" table="UserGroup"> - <key> - <column name="userName"/> - <column name="org"/> - </key> - <many-to-many class="Group"> - <column name="groupName"/> - <formula>org</formula> - </many-to-many> - </set> -</class> - -<class name="Group" table="`Group`"> - <composite-id> - <key-property name="name"/> - <key-property name="org"/> - </composite-id> - <property name="description"/> - <set name="users" table="UserGroup" inverse="true"> - <key> - <column name="groupName"/> - <column name="org"/> - </key> - <many-to-many class="User"> - <column name="userName"/> - <formula>org</formula> - </many-to-many> - </set> -</class> -]]></programlisting> - </sect2> - - <sect2 id="example-mappings-content-discrimination"> - <title>Content based discrimination</title> -<programlisting><![CDATA[<class name="Person" - discriminator-value="P"> - - <id name="id" - column="person_id" - unsaved-value="0"> - <generator class="native"/> - </id> - - - <discriminator - type="character"> - <formula> - case - when title is not null then 'E' - when salesperson is not null then 'C' - else 'P' - end - </formula> - </discriminator> - - <property name="name" - not-null="true" - length="80"/> - - <property name="sex" - not-null="true" - update="false"/> - - <component name="address"> - <property name="address"/> - <property name="zip"/> - <property name="country"/> - </component> - - <subclass name="Employee" - discriminator-value="E"> - <property name="title" - length="20"/> - <property name="salary"/> - <many-to-one name="manager"/> - </subclass> - - <subclass name="Customer" - discriminator-value="C"> - <property name="comments"/> - <many-to-one name="salesperson"/> - </subclass> - -</class>]]></programlisting> - </sect2> - - <sect2 id="example-mappings-association-alternatekeys" revision="2"> - <title>Associations on alternate keys</title> -<programlisting><![CDATA[<class name="Person"> - - <id name="id"> - <generator class="hilo"/> - </id> - - <property name="name" length="100"/> - - <one-to-one name="address" - property-ref="person" - cascade="all" - fetch="join"/> - - <set name="accounts" - inverse="true"> - <key column="userId" - property-ref="userId"/> - <one-to-many class="Account"/> - </set> - - <property name="userId" length="8"/> - -</class> - -<class name="Address"> - - <id name="id"> - <generator class="hilo"/> - </id> - - <property name="address" length="300"/> - <property name="zip" length="5"/> - <property name="country" length="25"/> - <many-to-one name="person" unique="true" not-null="true"/> - -</class> - -<class name="Account"> - <id name="accountId" length="32"> - <generator class="uuid"/> - </id> - - <many-to-one name="user" - column="userId" - property-ref="userId"/> - - <property name="type" not-null="true"/> - -</class>]]></programlisting> - </sect2> - - </sect1> - -</chapter> - Deleted: core/trunk/documentation/envers/src/main/docbook/en-US/content/example_parentchild.xml =================================================================== --- core/trunk/documentation/envers/src/main/docbook/en-US/content/example_parentchild.xml 2008-11-04 17:31:01 UTC (rev 15499) +++ core/trunk/documentation/envers/src/main/docbook/en-US/content/example_parentchild.xml 2008-11-04 17:31:43 UTC (rev 15500) @@ -1,388 +0,0 @@ -<?xml version='1.0' encoding="UTF-8"?> -<!-- - ~ Hibernate, Relational Persistence for Idiomatic Java - ~ - ~ Copyright (c) 2008, Red Hat Middleware LLC or third-party contributors as - ~ indicated by the @author tags or express copyright attribution - ~ statements applied by the authors. All third-party contributions are - ~ distributed under license by Red Hat Middleware LLC. - ~ - ~ This copyrighted material is made available to anyone wishing to use, modify, - ~ copy, or redistribute it subject to the terms and conditions of the GNU - ~ Lesser General Public License, as published by the Free Software Foundation. - ~ - ~ This program is distributed in the hope that it will be useful, - ~ but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY - ~ or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License - ~ for more details. - ~ - ~ You should have received a copy of the GNU Lesser General Public License - ~ along with this distribution; if not, write to: - ~ Free Software Foundation, Inc. - ~ 51 Franklin Street, Fifth Floor - ~ Boston, MA 02110-1301 USA - --> - -<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd"> - -<chapter id="example-parentchild"> - <title>Example: Parent/Child</title> - - <para> - One of the very first things that new users try to do with Hibernate is to model a parent / child type - relationship. There are two different approaches to this. For various reasons the most convenient - approach, especially for new users, is to model both <literal>Parent</literal> and <literal>Child</literal> - as entity classes with a <literal>&lt;one-to-many&gt;</literal> association from <literal>Parent</literal> - to <literal>Child</literal>. (The alternative approach is to declare the <literal>Child</literal> as a - <literal>&lt;composite-element&gt;</literal>.) Now, it turns out that default semantics of a one to many - association (in Hibernate) are much less close to the usual semantics of a parent / child relationship than - those of a composite element mapping. We will explain how to use a <emphasis>bidirectional one to many - association with cascades</emphasis> to model a parent / child relationship efficiently and elegantly. - It's not at all difficult! - </para> - - <sect1 id="example-parentchild-collections"> - <title>A note about collections</title> - - <para> - Hibernate collections are considered to be a logical part of their owning entity; never of the - contained entities. This is a crucial distinction! It has the following consequences: - </para> - - <itemizedlist> - <listitem> - <para> - When we remove / add an object from / to a collection, the version number of the collection owner - is incremented. - </para> - </listitem> - <listitem> - <para> - If an object that was removed from a collection is an instance of a value type (eg, a composite - element), that object will cease to be persistent and its state will be completely removed from - the database. Likewise, adding a value type instance to the collection will cause its state to be - immediately persistent. - </para> - </listitem> - <listitem> - <para> - On the other hand, if an entity is removed from a collection (a one-to-many or many-to-many - association), it will not be deleted, by default. This behaviour is completely consistent - a - change to the internal state of another entity should not cause the associated entity to vanish! - Likewise, adding an entity to a collection does not cause that entity to become persistent, by - default. - </para> - </listitem> - </itemizedlist> - - <para> - Instead, the default behaviour is that adding an entity to a collection merely creates a link between - the two entities, while removing it removes the link. This is very appropriate for all sorts of cases. - Where it is not appropriate at all is the case of a parent / child relationship, where the life of the - child is bound to the life cycle of the parent. - </para> - - </sect1> - - <sect1 id="example-parentchild-bidir"> - <title>Bidirectional one-to-many</title> - - <para> - Suppose we start with a simple <literal>&lt;one-to-many&gt;</literal> association from - <literal>Parent</literal> to <literal>Child</literal>. - </para> - - <programlisting><![CDATA[<set name="children"> - <key column="parent_id"/> - <one-to-many class="Child"/> -</set>]]></programlisting> - - <para> - If we were to execute the following code - </para> - - <programlisting><![CDATA[Parent p = .....; -Child c = new Child(); -p.getChildren().add(c); -session.save(c); -session.flush();]]></programlisting> - - <para> - Hibernate would issue two SQL statements: - </para> - - <itemizedlist> - <listitem> - <para>an <literal>INSERT</literal> to create the record for <literal>c</literal></para> - </listitem> - <listitem> - <para> - an <literal>UPDATE</literal> to create the link from <literal>p</literal> to - <literal>c</literal> - </para> - </listitem> - </itemizedlist> - - <para> - This is not only inefficient, but also violates any <literal>NOT NULL</literal> constraint on the - <literal>parent_id</literal> column. We can fix the nullability constraint violation by specifying - <literal>not-null="true"</literal> in the collection mapping: - </para> - - <programlisting><![CDATA[<set name="children"> - <key column="parent_id" not-null="true"/> - <one-to-many class="Child"/> -</set>]]></programlisting> - - <para> - However, this is not the recommended solution. - </para> - <para> - The underlying cause of this behaviour is that the link (the foreign key <literal>parent_id</literal>) - from <literal>p</literal> to <literal>c</literal> is not considered part of the state of the - <literal>Child</literal> object and is therefore not created in the <literal>INSERT</literal>. So the - solution is to make the link part of the <literal>Child</literal> mapping. - </para> - - <programlisting><![CDATA[<many-to-one name="parent" column="parent_id" not-null="true"/>]]></programlisting> - - <para> - (We also need to add the <literal>parent</literal> property to the <literal>Child</literal> class.) - </para> - - <para> - Now that the <literal>Child</literal> entity is managing the state of the link, we tell the collection - not to update the link. We use the <literal>inverse</literal> attribute. - </para> - - <programlisting><![CDATA[<set name="children" inverse="true"> - <key column="parent_id"/> - <one-to-many class="Child"/> -</set>]]></programlisting> - - <para> - The following code would be used to add a new <literal>Child</literal> - </para> - - <programlisting><![CDATA[Parent p = (Parent) session.load(Parent.class, pid); -Child c = new Child(); -c.setParent(p); -p.getChildren().add(c); -session.save(c); -session.flush();]]></programlisting> - - <para> - And now, only one SQL <literal>INSERT</literal> would be issued! - </para> - - <para> - To tighten things up a bit, we could create an <literal>addChild()</literal> method of - <literal>Parent</literal>. - </para> - - <programlisting><![CDATA[public void addChild(Child c) { - c.setParent(this); - children.add(c); -}]]></programlisting> - - <para> - Now, the code to add a <literal>Child</literal> looks like - </para> - - <programlisting><![CDATA[Parent p = (Parent) session.load(Parent.class, pid); -Child c = new Child(); -p.addChild(c); -session.save(c); -session.flush();]]></programlisting> - - </sect1> - - <sect1 id="example-parentchild-cascades"> - <title>Cascading life cycle</title> - - <para> - The explicit call to <literal>save()</literal> is still annoying. We will address this by - using cascades. - </para> - - <programlisting><![CDATA[<set name="children" inverse="true" cascade="all"> - <key column="parent_id"/> - <one-to-many class="Child"/> -</set>]]></programlisting> - - <para> - This simplifies the code above to - </para> - - <programlisting><![CDATA[Parent p = (Parent) session.load(Parent.class, pid); -Child c = new Child(); -p.addChild(c); -session.flush();]]></programlisting> - - <para> - Similarly, we don't need to iterate over the children when saving or deleting a <literal>Parent</literal>. - The following removes <literal>p</literal> and all its children from the database. - </para> - - <programlisting><![CDATA[Parent p = (Parent) session.load(Parent.class, pid); -session.delete(p); -session.flush();]]></programlisting> - - <para> - However, this code - </para> - - <programlisting><![CDATA[Parent p = (Parent) session.load(Parent.class, pid); -Child c = (Child) p.getChildren().iterator().next(); -p.getChildren().remove(c); -c.setParent(null); -session.flush();]]></programlisting> - - <para> - will not remove <literal>c</literal> from the database; it will ony remove the link to <literal>p</literal> - (and cause a <literal>NOT NULL</literal> constraint violation, in this case). You need to explicitly - <literal>delete()</literal> the <literal>Child</literal>. - </para> - - <programlisting><![CDATA[Parent p = (Parent) session.load(Parent.class, pid); -Child c = (Child) p.getChildren().iterator().next(); -p.getChildren().remove(c); -session.delete(c); -session.flush();]]></programlisting> - - <para> - Now, in our case, a <literal>Child</literal> can't really exist without its parent. So if we remove - a <literal>Child</literal> from the collection, we really do want it to be deleted. For this, we must - use <literal>cascade="all-delete-orphan"</literal>. - </para> - - <programlisting><![CDATA[<set name="children" inverse="true" cascade="all-delete-orphan"> - <key column="parent_id"/> - <one-to-many class="Child"/> -</set>]]></programlisting> - - <para> - Note: even though the collection mapping specifies <literal>inverse="true"</literal>, cascades are - still processed by iterating the collection elements. So if you require that an object be saved, - deleted or updated by cascade, you must add it to the collection. It is not enough to simply call - <literal>setParent()</literal>. - </para> - - </sect1> - - <sect1 id="example-parentchild-update"> - <title>Cascades and <literal>unsaved-value</literal></title> - - <para> - Suppose we loaded up a <literal>Parent</literal> in one <literal>Session</literal>, made some changes - in a UI action and wish to persist these changes in a new session by calling <literal>update()</literal>. - The <literal>Parent</literal> will contain a collection of childen and, since cascading update is enabled, - Hibernate needs to know which children are newly instantiated and which represent existing rows in the - database. Lets assume that both <literal>Parent</literal> and <literal>Child</literal> have genenerated - identifier properties of type <literal>Long</literal>. Hibernate will use the identifier and - version/timestamp property value to determine which of the children are new. (See - <xref linkend="objectstate-saveorupdate"/>.) <emphasis>In Hibernate3, it is no longer necessary to specify - an <literal>unsaved-value</literal> explicitly.</emphasis> - </para> - - <para> - The following code will update <literal>parent</literal> and <literal>child</literal> and insert - <literal>newChild</literal>. - </para> - - <programlisting><![CDATA[//parent and child were both loaded in a previous session -parent.addChild(child); -Child newChild = new Child(); -parent.addChild(newChild); -session.update(parent); -session.flush();]]></programlisting> - - <para> - Well, that's all very well for the case of a generated identifier, but what about assigned identifiers - and composite identifiers? This is more difficult, since Hibernate can't use the identifier property to - distinguish between a newly instantiated object (with an identifier assigned by the user) and an - object loaded in a previous session. In this case, Hibernate will either use the timestamp or version - property, or will actually query the second-level cache or, worst case, the database, to see if the - row exists. - </para> - - <!-- undocumenting - <para> - There is one further possibility. The <literal>Interceptor</literal> method named - <literal>isUnsaved()</literal> lets the application implement its own strategy for distinguishing - newly instantiated objects. For example, you could define a base class for your persistent classes. - </para> - - <programlisting><![CDATA[public class Persistent { - private boolean _saved = false; - public void onSave() { - _saved=true; - } - public void onLoad() { - _saved=true; - } - ...... - public boolean isSaved() { - return _saved; - } -}]]></programlisting> - - <para> - (The <literal>saved</literal> property is non-persistent.) - Now implement <literal>isUnsaved()</literal>, along with <literal>onLoad()</literal> - and <literal>onSave()</literal> as follows. - </para> - - <programlisting><![CDATA[public Boolean isUnsaved(Object entity) { - if (entity instanceof Persistent) { - return new Boolean( !( (Persistent) entity ).isSaved() ); - } - else { - return null; - } -} - -public boolean onLoad(Object entity, - Serializable id, - Object[] state, - String[] propertyNames, - Type[] types) { - - if (entity instanceof Persistent) ( (Persistent) entity ).onLoad(); - return false; -} - -public boolean onSave(Object entity, - Serializable id, - Object[] state, - String[] propertyNames, - Type[] types) { - - if (entity instanceof Persistent) ( (Persistent) entity ).onSave(); - return false; -}]]></programlisting> - - <para> - Don't worry; in Hibernate3 you don't need to write any of this kind of code if you don't want to. - </para> - --> - </sect1> - - <sect1 id="example-parentchild-conclusion"> - <title>Conclusion</title> - - <para> - There is quite a bit to digest here and it might look confusing first time around. However, in practice, - it all works out very nicely. Most Hibernate applications use the parent / child pattern in many places. - </para> - - <para> - We mentioned an alternative in the first paragraph. None of the above issues exist in the case of - <literal>&lt;composite-element&gt;</literal> mappings, which have exactly the semantics of a parent / child - relationship. Unfortunately, there are two big limitations to composite element classes: composite elements - may not own collections, and they should not be the child of any entity other than the unique parent. - </para> - - </sect1> - -</chapter> Deleted: core/trunk/documentation/envers/src/main/docbook/en-US/content/example_weblog.xml =================================================================== --- core/trunk/documentation/envers/src/main/docbook/en-US/content/example_weblog.xml 2008-11-04 17:31:01 UTC (rev 15499) +++ core/trunk/documentation/envers/src/main/docbook/en-US/content/example_weblog.xml 2008-11-04 17:31:43 UTC (rev 15500) @@ -1,457 +0,0 @@ -<?xml version='1.0' encoding="UTF-8"?> -<!-- - ~ Hibernate, Relational Persistence for Idiomatic Java - ~ - ~ Copyright (c) 2008, Red Hat Middleware LLC or third-party contributors as - ~ indicated by the @author tags or express copyright attribution - ~ statements applied by the authors. All third-party contributions are - ~ distributed under license by Red Hat Middleware LLC. - ~ - ~ This copyrighted material is made available to anyone wishing to use, modify, - ~ copy, or redistribute it subject to the terms and conditions of the GNU - ~ Lesser General Public License, as published by the Free Software Foundation. - ~ - ~ This program is distributed in the hope that it will be useful, - ~ but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY - ~ or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License - ~ for more details. - ~ - ~ You should have received a copy of the GNU Lesser General Public License - ~ along with this distribution; if not, write to: - ~ Free Software Foundation, Inc. - ~ 51 Franklin Street, Fifth Floor - ~ Boston, MA 02110-1301 USA - --> - -<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd"> - -<chapter id="example-weblog"> - <title>Example: Weblog Application</title> - - <sect1 id="example-weblog-classes"> - <title>Persistent Classes</title> - - <para> - The persistent classes represent a weblog, and an item posted - in a weblog. They are to be modelled as a standard parent/child - relationship, but we will use an ordered bag, instead of a set. - </para> - - <programlisting><![CDATA[package eg; - -import java.util.List; - -public class Blog { - private Long _id; - private String _name; - private List _items; - - public Long getId() { - return _id; - } - public List getItems() { - return _items; - } - public String getName() { - return _name; - } - public void setId(Long long1) { - _id = long1; - } - public void setItems(List list) { - _items = list; - } - public void setName(String string) { - _name = string; - } -}]]></programlisting> - - <programlisting><![CDATA[package eg; - -import java.text.DateFormat; -import java.util.Calendar; - -public class BlogItem { - private Long _id; - private Calendar _datetime; - private String _text; - private String _title; - private Blog _blog; - - public Blog getBlog() { - return _blog; - } - public Calendar getDatetime() { - return _datetime; - } - public Long getId() { - return _id; - } - public String getText() { - return _text; - } - public String getTitle() { - return _title; - } - public void setBlog(Blog blog) { - _blog = blog; - } - public void setDatetime(Calendar calendar) { - _datetime = calendar; - } - public void setId(Long long1) { - _id = long1; - } - public void setText(String string) { - _text = string; - } - public void setTitle(String string) { - _title = string; - } -}]]></programlisting> - - </sect1> - - <sect1 id="example-weblog-mappings"> - <title>Hibernate Mappings</title> - - <para> - The XML mappings should now be quite straightforward. - </para> - - <programlisting><![CDATA[<?xml version="1.0"?> -<!DOCTYPE hibernate-mapping PUBLIC - "-//Hibernate/Hibernate Mapping DTD 3.0//EN" - "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> - -<hibernate-mapping package="eg"> - - <class - name="Blog" - table="BLOGS"> - - <id - name="id" - column="BLOG_ID"> - - <generator class="native"/> - - </id> - - <property - name="name" - column="NAME" - not-null="true" - unique="true"/> - - <bag - name="items" - inverse="true" - order-by="DATE_TIME" - cascade="all"> - - <key column="BLOG_ID"/> - <one-to-many class="BlogItem"/> - - </bag> - - </class> - -</hibernate-mapping>]]></programlisting> - - <programlisting><![CDATA[<?xml version="1.0"?> -<!DOCTYPE hibernate-mapping PUBLIC - "-//Hibernate/Hibernate Mapping DTD 3.0//EN" - "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> - -<hibernate-mapping package="eg"> - - <class - name="BlogItem" - table="BLOG_ITEMS" - dynamic-update="true"> - - <id - name="id" - column="BLOG_ITEM_ID"> - - <generator class="native"/> - - </id> - - <property - name="title" - column="TITLE" - not-null="true"/> - - <property - name="text" - column="TEXT" - not-null="true"/> - - <property - name="datetime" - column="DATE_TIME" - not-null="true"/> - - <many-to-one - name="blog" - column="BLOG_ID" - not-null="true"/> - - </class> - -</hibernate-mapping>]]></programlisting> - - </sect1> - - <sect1 id="example-weblog-code"> - <title>Hibernate Code</title> - - <para> - The following class demonstrates some of the kinds of things - we can do with these classes, using Hibernate. - </para> - - <programlisting><![CDATA[package eg; - -import java.util.ArrayList; -import java.util.Calendar; -import java.util.Iterator; -import java.util.List; - -import org.hibernate.HibernateException; -import org.hibernate.Query; -import org.hibernate.Session; -import org.hibernate.SessionFactory; -import org.hibernate.Transaction; -import org.hibernate.cfg.Configuration; -import org.hibernate.tool.hbm2ddl.SchemaExport; - -public class BlogMain { - - private SessionFactory _sessions; - - public void configure() throws HibernateException { - _sessions = new Configuration() - .addClass(Blog.class) - .addClass(BlogItem.class) - .buildSessionFactory(); - } - - public void exportTables() throws HibernateException { - Configuration cfg = new Configuration() - .addClass(Blog.class) - .addClass(BlogItem.class); - new SchemaExport(cfg).create(true, true); - } - - public Blog createBlog(String name) throws HibernateException { - - Blog blog = new Blog(); - blog.setName(name); - blog.setItems( new ArrayList() ); - - Session session = _sessions.openSession(); - Transaction tx = null; - try { - tx = session.beginTransaction(); - session.persist(blog); - tx.commit(); - } - catch (HibernateException he) { - if (tx!=null) tx.rollback(); - throw he; - } - finally { - session.close(); - } - return blog; - } - - public BlogItem createBlogItem(Blog blog, String title, String text) - throws HibernateException { - - BlogItem item = new BlogItem(); - item.setTitle(title); - item.setText(text); - item.setBlog(blog); - item.setDatetime( Calendar.getInstance() ); - blog.getItems().add(item); - - Session session = _sessions.openSession(); - Transaction tx = null; - try { - tx = session.beginTransaction(); - session.update(blog); - tx.commit(); - } - catch (HibernateException he) { - if (tx!=null) tx.rollback(); - throw he; - } - finally { - session.close(); - } - return item; - } - - public BlogItem createBlogItem(Long blogid, String title, String text) - throws HibernateException { - - BlogItem item = new BlogItem(); - item.setTitle(title); - item.setText(text); - item.setDatetime( Calendar.getInstance() ); - - Session session = _sessions.openSession(); - Transaction tx = null; - try { - tx = session.beginTransaction(); - Blog blog = (Blog) session.load(Blog.class, blogid); - item.setBlog(blog); - blog.getItems().add(item); - tx.commit(); - } - catch (HibernateException he) { - if (tx!=null) tx.rollback(); - throw he; - } - finally { - session.close(); - } - return item; - } - - public void updateBlogItem(BlogItem item, String text) - throws HibernateException { - - item.setText(text); - - Session session = _sessions.openSession(); - Transaction tx = null; - try { - tx = session.beginTransaction(); - session.update(item); - tx.commit(); - } - catch (HibernateException he) { - if (tx!=null) tx.rollback(); - throw he; - } - finally { - session.close(); - } - } - - public void updateBlogItem(Long itemid, String text) - throws HibernateException { - - Session session = _sessions.openSession(); - Transaction tx = null; - try { - tx = session.beginTransaction(); - BlogItem item = (BlogItem) session.load(BlogItem.class, itemid); - item.setText(text); - tx.commit(); - } - catch (HibernateException he) { - if (tx!=null) tx.rollback(); - throw he; - } - finally { - session.close(); - } - } - - public List listAllBlogNamesAndItemCounts(int max) - throws HibernateException { - - Session session = _sessions.openSession(); - Transaction tx = null; - List result = null; - try { - tx = session.beginTransaction(); - Query q = session.createQuery( - "select blog.id, blog.name, count(blogItem) " + - "from Blog as blog " + - "left outer join blog.items as blogItem " + - "group by blog.name, blog.id " + - "order by max(blogItem.datetime)" - ); - q.setMaxResults(max); - result = q.list(); - tx.commit(); - } - catch (HibernateException he) { - if (tx!=null) tx.rollback(); - throw he; - } - finally { - session.close(); - } - return result; - } - - public Blog getBlogAndAllItems(Long blogid) - throws HibernateException { - - Session session = _sessions.openSession(); - Transaction tx = null; - Blog blog = null; - try { - tx = session.beginTransaction(); - Query q = session.createQuery( - "from Blog as blog " + - "left outer join fetch blog.items " + - "where blog.id = :blogid" - ); - q.setParameter("blogid", blogid); - blog = (Blog) q.uniqueResult(); - tx.commit(); - } - catch (HibernateException he) { - if (tx!=null) tx.rollback(); - throw he; - } - finally { - session.close(); - } - return blog; - } - - public List listBlogsAndRecentItems() throws HibernateException { - - Session session = _sessions.openSession(); - Transaction tx = null; - List result = null; - try { - tx = session.beginTransaction(); - Query q = session.createQuery( - "from Blog as blog " + - "inner join blog.items as blogItem " + - "where blogItem.datetime > :minDate" - ); - - Calendar cal = Calendar.getInstance(); - cal.roll(Calendar.MONTH, false); - q.setCalendar("minDate", cal); - - result = q.list(); - tx.commit(); - } - catch (HibernateException he) { - if (tx!=null) tx.rollback(); - throw he; - } - finally { - session.close(); - } - return result; - } -}]]></programlisting> - - </sect1> - -</chapter> - Deleted: core/trunk/documentation/envers/src/main/docbook/en-US/content/filters.xml =================================================================== --- core/trunk/documentation/envers/src/main/docbook/en-US/content/filters.xml 2008-11-04 17:31:01 UTC (rev 15499) +++ core/trunk/documentation/envers/src/main/docbook/en-US/content/filters.xml 2008-11-04 17:31:43 UTC (rev 15500) @@ -1,173 +0,0 @@ -<?xml version='1.0' encoding="UTF-8"?> -<!-- - ~ Hibernate, Relational Persistence for Idiomatic Java - ~ - ~ Copyright (c) 2008, Red Hat Middleware LLC or third-party contributors as - ~ indicated by the @author tags or express copyright attribution - ~ statements applied by the authors. All third-party contributions are - ~ distributed under license by Red Hat Middleware LLC. - ~ - ~ This copyrighted material is made available to anyone wishing to use, modify, - ~ copy, or redistribute it subject to the terms and conditions of the GNU - ~ Lesser General Public License, as published by the Free Software Foundation. - ~ - ~ This program is distributed in the hope that it will be useful, - ~ but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY - ~ or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License - ~ for more details. - ~ - ~ You should have received a copy of the GNU Lesser General Public License - ~ along with this distribution; if not, write to: - ~ Free Software Foundation, Inc. - ~ 51 Franklin Street, Fifth Floor - ~ Boston, MA 02110-1301 USA - --> - -<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd"> - -<chapter id="filters"> - <title>Filtering data</title> - - <para> - Hibernate3 provides an innovative new approach to handling data with "visibility" rules. - A <emphasis>Hibernate filter</emphasis> is a global, named, parameterized filter that may be - enabled or disabled for a particular Hibernate session. - </para> - - <sect1 id="objectstate-filters" revision="1"> - <title>Hibernate filters</title> - - <para> - Hibernate3 adds the ability to pre-define filter criteria and attach those filters at both - a class and a collection level. A filter criteria is the ability to define a restriction clause - very similiar to the existing "where" attribute available on the class and various collection - elements. Except these filter conditions can be parameterized. The application can then make - the decision at runtime whether given filters should be enabled and what their parameter - values should be. Filters can be used like database views, but parameterized inside the - application. - </para> - - <para> - In order to use filters, they must first be defined and then attached to the appropriate - mapping elements. To define a filter, use the <literal>&lt;filter-def/&gt;</literal> element - within a <literal>&lt;hibernate-mapping/&gt;</literal> element: - </para> - - <programlisting><![CDATA[<filter-def name="myFilter"> - <filter-param name="myFilterParam" type="string"/> -</filter-def>]]></programlisting> - - <para> - Then, this filter can be attached to a class: - </para> - - <programlisting><![CDATA[<class name="myClass" ...> - ... - <filter name="myFilter" condition=":myFilterParam = MY_FILTERED_COLUMN"/> -</class>]]></programlisting> - - <para> - or, to a collection: - </para> - - <programlisting><![CDATA[<set ...> - <filter name="myFilter" condition=":myFilterParam = MY_FILTERED_COLUMN"/> -</set>]]></programlisting> - - <para> - or, even to both (or multiples of each) at the same time. - </para> - - <para> - The methods on <literal>Session</literal> are: <literal>enableFilter(String filterName)</literal>, - <literal>getEnabledFilter(String filterName)</literal>, and <literal>disableFilter(String filterName)</literal>. - By default, filters are <emphasis>not</emphasis> enabled for a given session; they must be explcitly - enabled through use of the <literal>Session.enableFilter()</literal> method, which returns an - instance of the <literal>Filter</literal> interface. Using the simple filter defined above, this - would look like: - </para> - - <programlisting><![CDATA[session.enableFilter("myFilter").setParameter("myFilterParam", "some-value");]]></programlisting> - - <para> - Note that methods on the org.hibernate.Filter interface do allow the method-chaining common to much of Hibernate. - </para> - - <para> - A full example, using temporal data with an effective record date pattern: - </para> - - <programlisting><![CDATA[<filter-def name="effectiveDate"> - <filter-param name="asOfDate" type="date"/> -</filter-def> - -<class name="Employee" ...> -... - <many-to-one name="department" column="dept_id" class="Department"/> - <property name="effectiveStartDate" type="date" column="eff_start_dt"/> - <property name="effectiveEndDate" type="date" column="eff_end_dt"/> -... - <!-- - Note that this assumes non-terminal records have an eff_end_dt set to - a max db date for simplicity-sake - --> - <filter name="effectiveDate" - condition=":asOfDate BETWEEN eff_start_dt and eff_end_dt"/> -</class> - -<class name="Department" ...> -... - <set name="employees" lazy="true"> - <key column="dept_id"/> - <one-to-many class="Employee"/> - <filter name="effectiveDate" - condition=":asOfDate BETWEEN eff_start_dt and eff_end_dt"/> - </set> -</class>]]></programlisting> - - <para> - Then, in order to ensure that you always get back currently effective records, simply - enable the filter on the session prior to retrieving employee data: - </para> - -<programlisting><![CDATA[Session session = ...; -session.enableFilter("effectiveDate").setParameter("asOfDate", new Date()); -List results = session.createQuery("from Employee as e where e.salary > :targetSalary") - .setLong("targetSalary", new Long(1000000)) - .list(); -]]></programlisting> - - <para> - In the HQL above, even though we only explicitly mentioned a salary constraint on the results, - because of the enabled filter the query will return only currently active employees who have - a salary greater than a million dollars. - </para> - - <para> - Note: if you plan on using filters with outer joining (either through HQL or load fetching) be - careful of the direction of the condition expression. Its safest to set this up for left - outer joining; in general, place the parameter first followed by the column name(s) after - the operator. - </para> - - <para> - After being defined a filter might be attached to multiple entities and/or - collections each with its own condition. That can be tedious when the - conditions are the same each time. Thus <literal>&lt;filter-def/&gt;</literal> - allows defining a default condition, either as an attribute or CDATA: - </para> - - <programlisting><![CDATA[<filter-def name="myFilter" condition="abc > xyz">...</filter-def> -<filter-def name="myOtherFilter">abc=xyz</filter-def>]]></programlisting> - - <para> - This default condition will then be used whenever the filter is attached to something - without specifying a condition. Note that this means you can give a specific condition - as part of the attachment of the filter which overrides the default condition in that - particular case. - </para> - - </sect1> - -</chapter> - Deleted: core/trunk/documentation/envers/src/main/docbook/en-US/content/inheritance_mapping.xml =================================================================== --- core/trunk/documentation/envers/src/main/docbook/en-US/content/inheritance_mapping.xml 2008-11-04 17:31:01 UTC (rev 15499) +++ core/trunk/documentation/envers/src/main/docbook/en-US/content/inheritance_mapping.xml 2008-11-04 17:31:43 UTC (rev 15500) @@ -1,518 +0,0 @@ -<?xml version='1.0' encoding="UTF-8"?> -<!-- - ~ Hibernate, Relational Persistence for Idiomatic Java - ~ - ~ Copyright (c) 2008, Red Hat Middleware LLC or third-party contributors as - ~ indicated by the @author tags or express copyright attribution - ~ statements applied by the authors. All third-party contributions are - ~ distributed under license by Red Hat Middleware LLC. - ~ - ~ This copyrighted material is made available to anyone wishing to use, modify, - ~ copy, or redistribute it subject to the terms and conditions of the GNU - ~ Lesser General Public License, as published by the Free Software Foundation. - ~ - ~ This program is distributed in the hope that it will be useful, - ~ but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY - ~ or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License - ~ for more details. - ~ - ~ You should have received a copy of the GNU Lesser General Public License - ~ along with this distribution; if not, write to: - ~ Free Software Foundation, Inc. - ~ 51 Franklin Street, Fifth Floor - ~ Boston, MA 02110-1301 USA - --> - -<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd"> - -<chapter id="inheritance"> - <title>Inheritance Mapping</title> - - <sect1 id="inheritance-strategies" revision="3"> - <title>The Three Strategies</title> - - <para> - Hibernate supports the three basic inheritance mapping strategies: - </para> - - <itemizedlist> - <listitem> - <para> - table per class hierarchy - </para> - </listitem> - <listitem> - <para> - table per subclass - </para> - </listitem> - <listitem> - <para> - table per concrete class - </para> - </listitem> - </itemizedlist> - - <para> - In addition, Hibernate supports a fourth, slightly different kind of - polymorphism: - </para> - - <itemizedlist> - <listitem> - <para> - implicit polymorphism - </para> - </listitem> - </itemizedlist> - - <para> - It is possible to use different mapping strategies for different - branches of the same inheritance hierarchy, and then make use of implicit - polymorphism to achieve polymorphism across the whole hierarchy. However, - Hibernate does not support mixing <literal>&lt;subclass&gt;</literal>, - and <literal>&lt;joined-subclass&gt;</literal> and - <literal>&lt;union-subclass&gt;</literal> mappings under the same root - <literal>&lt;class&gt;</literal> element. It is possible to mix together - the table per hierarchy and table per subclass strategies, under the - the same <literal>&lt;class&gt;</literal> element, by combining the - <literal>&lt;subclass&gt;</literal> and <literal>&lt;join&gt;</literal> - elements (see below). - </para> - - <para> - It is possible to define <literal>subclass</literal>, <literal>union-subclass</literal>, - and <literal>joined-subclass</literal> mappings in separate mapping documents, directly beneath - <literal>hibernate-mapping</literal>. This allows you to extend a class hierachy just by adding - a new mapping file. You must specify an <literal>extends</literal> attribute in the subclass mapping, - naming a previously mapped superclass. Note: Previously this feature made the ordering of the mapping - documents important. Since Hibernate3, the ordering of mapping files does not matter when using the - extends keyword. The ordering inside a single mapping file still needs to be defined as superclasses - before subclasses. - </para> - - <programlisting><![CDATA[ - <hibernate-mapping> - <subclass name="DomesticCat" extends="Cat" discriminator-value="D"> - <property name="name" type="string"/> - </subclass> - </hibernate-mapping>]]></programlisting> - - - <sect2 id="inheritance-tableperclass" > - <title>Table per class hierarchy</title> - - <para> - Suppose we have an interface <literal>Payment</literal>, with implementors - <literal>CreditCardPayment</literal>, <literal>CashPayment</literal>, - <literal>ChequePayment</literal>. The table per hierarchy mapping would - look like: - </para> - - <programlisting><![CDATA[<class name="Payment" table="PAYMENT"> - <id name="id" type="long" column="PAYMENT_ID"> - <generator class="native"/> - </id> - <discriminator column="PAYMENT_TYPE" type="string"/> - <property name="amount" column="AMOUNT"/> - ... - <subclass name="CreditCardPayment" discriminator-value="CREDIT"> - <property name="creditCardType" column="CCTYPE"/> - ... - </subclass> - <subclass name="CashPayment" discriminator-value="CASH"> - ... - </subclass> - <subclass name="ChequePayment" discriminator-value="CHEQUE"> - ... - </subclass> -</class>]]></programlisting> - - <para> - Exactly one table is required. There is one big limitation of this mapping - strategy: columns declared by the subclasses, such as <literal>CCTYPE</literal>, - may not have <literal>NOT NULL</literal> constraints. - </para> - - </sect2> - - <sect2 id="inheritance-tablepersubclass"> - <title>Table per subclass</title> - - <para> - A table per subclass mapping would look like: - </para> - - <programlisting><![CDATA[<class name="Payment" table="PAYMENT"> - <id name="id" type="long" column="PAYMENT_ID"> - <generator class="native"/> - </id> - <property name="amount" column="AMOUNT"/> - ... - <joined-subclass name="CreditCardPayment" table="CREDIT_PAYMENT"> - <key column="PAYMENT_ID"/> - <property name="creditCardType" column="CCTYPE"/> - ... - </joined-subclass> - <joined-subclass name="CashPayment" table="CASH_PAYMENT"> - <key column="PAYMENT_ID"/> - ... - </joined-subclass> - <joined-subclass name="ChequePayment" table="CHEQUE_PAYMENT"> - <key column="PAYMENT_ID"/> - ... - </joined-subclass> -</class>]]></programlisting> - - <para> - Four tables are required. The three subclass tables have primary - key associations to the superclass table (so the relational model - is actually a one-to-one association). - </para> - - </sect2> - - <sect2 id="inheritance-tablepersubclass-discriminator" revision="2"> - <title>Table per subclass, using a discriminator</title> - - <para> - Note that Hibernate's implementation of table per subclass requires - no discriminator column. Other object/relational mappers use a - different implementation of table per subclass which requires a type - discriminator column in the superclass table. The approach taken by - Hibernate is much more difficult to implement but arguably more - correct from a relational point of view. If you would like to use - a discriminator column with the table per subclass strategy, you - may combine the use of <literal>&lt;subclass&gt;</literal> and - <literal>&lt;join&gt;</literal>, as follow: - </para> - - <programlisting><![CDATA[<class name="Payment" table="PAYMENT"> - <id name="id" type="long" column="PAYMENT_ID"> - <generator class="native"/> - </id> - <discriminator column="PAYMENT_TYPE" type="string"/> - <property name="amount" column="AMOUNT"/> - ... - <subclass name="CreditCardPayment" discriminator-value="CREDIT"> - <join table="CREDIT_PAYMENT"> - <key column="PAYMENT_ID"/> - <property name="creditCardType" column="CCTYPE"/> - ... - </join> - </subclass> - <subclass name="CashPayment" discriminator-value="CASH"> - <join table="CASH_PAYMENT"> - <key column="PAYMENT_ID"/> - ... - </join> - </subclass> - <subclass name="ChequePayment" discriminator-value="CHEQUE"> - <join table="CHEQUE_PAYMENT" fetch="select"> - <key column="PAYMENT_ID"/> - ... - </join> - </subclass> -</class>]]></programlisting> - - <para> - The optional <literal>fetch="select"</literal> declaration tells Hibernate - not to fetch the <literal>ChequePayment</literal> subclass data using an - outer join when querying the superclass. - </para> - - </sect2> - - <sect2 id="inheritance-mixing-tableperclass-tablepersubclass"> - <title>Mixing table per class hierarchy with table per subclass</title> - - <para> - You may even mix the table per hierarchy and table per subclass strategies - using this approach: - </para> - - <programlisting><![CDATA[<class name="Payment" table="PAYMENT"> - <id name="id" type="long" column="PAYMENT_ID"> - <generator class="native"/> - </id> - <discriminator column="PAYMENT_TYPE" type="string"/> - <property name="amount" column="AMOUNT"/> - ... - <subclass name="CreditCardPayment" discriminator-value="CREDIT"> - <join table="CREDIT_PAYMENT"> - <property name="creditCardType" column="CCTYPE"/> - ... - </join> - </subclass> - <subclass name="CashPayment" discriminator-value="CASH"> - ... - </subclass> - <subclass name="ChequePayment" discriminator-value="CHEQUE"> - ... - </subclass> -</class>]]></programlisting> - - <para> - For any of these mapping strategies, a polymorphic association to the root - <literal>Payment</literal> class is mapped using - <literal>&lt;many-to-one&gt;</literal>. - </para> - - <programlisting><![CDATA[<many-to-one name="payment" column="PAYMENT_ID" class="Payment"/>]]></programlisting> - - </sect2> - - <sect2 id="inheritance-tableperconcrete" revision="2"> - <title>Table per concrete class</title> - - <para> - There are two ways we could go about mapping the table per concrete class - strategy. The first is to use <literal>&lt;union-subclass&gt;</literal>. - </para> - - <programlisting><![CDATA[<class name="Payment"> - <id name="id" type="long" column="PAYMENT_ID"> - <generator class="sequence"/> - </id> - <property name="amount" column="AMOUNT"/> - ... - <union-subclass name="CreditCardPayment" table="CREDIT_PAYMENT"> - <property name="creditCardType" column="CCTYPE"/> - ... - </union-subclass> - <union-subclass name="CashPayment" table="CASH_PAYMENT"> - ... - </union-subclass> - <union-subclass name="ChequePayment" table="CHEQUE_PAYMENT"> - ... - </union-subclass> -</class>]]></programlisting> - - <para> - Three tables are involved for the subclasses. Each table defines columns for - all properties of the class, including inherited properties. - </para> - - <para> - The limitation of this approach is that if a property is mapped on the - superclass, the column name must be the same on all subclass tables. - (We might relax this in a future release of Hibernate.) The identity - generator strategy is not allowed in union subclass inheritance, indeed - the primary key seed has to be shared accross all unioned subclasses - of a hierarchy. - </para> - - <para> - If your superclass is abstract, map it with <literal>abstract="true"</literal>. - Of course, if it is not abstract, an additional table (defaults to - <literal>PAYMENT</literal> in the example above) is needed to hold instances - of the superclass. - </para> - - </sect2> - - <sect2 id="inheritance-tableperconcreate-polymorphism"> - <title>Table per concrete class, using implicit polymorphism</title> - - <para> - An alternative approach is to make use of implicit polymorphism: - </para> - - <programlisting><![CDATA[<class name="CreditCardPayment" table="CREDIT_PAYMENT"> - <id name="id" type="long" column="CREDIT_PAYMENT_ID"> - <generator class="native"/> - </id> - <property name="amount" column="CREDIT_AMOUNT"/> - ... -</class> - -<class name="CashPayment" table="CASH_PAYMENT"> - <id name="id" type="long" column="CASH_PAYMENT_ID"> - <generator class="native"/> - </id> - <property name="amount" column="CASH_AMOUNT"/> - ... -</class> - -<class name="ChequePayment" table="CHEQUE_PAYMENT"> - <id name="id" type="long" column="CHEQUE_PAYMENT_ID"> - <generator class="native"/> - </id> - <property name="amount" column="CHEQUE_AMOUNT"/> - ... -</class>]]></programlisting> - - <para> - Notice that nowhere do we mention the <literal>Payment</literal> interface - explicitly. Also notice that properties of <literal>Payment</literal> are - mapped in each of the subclasses. If you want to avoid duplication, consider - using XML entities - (e.g. <literal>[ &lt;!ENTITY allproperties SYSTEM "allproperties.xml"&gt; ]</literal> - in the <literal>DOCTYPE</literal> declartion and - <literal>&amp;allproperties;</literal> in the mapping). - </para> - - <para> - The disadvantage of this approach is that Hibernate does not generate SQL - <literal>UNION</literal>s when performing polymorphic queries. - </para> - - <para> - For this mapping strategy, a polymorphic association to <literal>Payment</literal> - is usually mapped using <literal>&lt;any&gt;</literal>. - </para> - - <programlisting><![CDATA[<any name="payment" meta-type="string" id-type="long"> - <meta-value value="CREDIT" class="CreditCardPayment"/> - <meta-value value="CASH" class="CashPayment"/> - <meta-value value="CHEQUE" class="ChequePayment"/> - <column name="PAYMENT_CLASS"/> - <column name="PAYMENT_ID"/> -</any>]]></programlisting> - - </sect2> - - <sect2 id="inheritace-mixingpolymorphism"> - <title>Mixing implicit polymorphism with other inheritance mappings</title> - - <para> - There is one further thing to notice about this mapping. Since the subclasses - are each mapped in their own <literal>&lt;class&gt;</literal> element (and since - <literal>Payment</literal> is just an interface), each of the subclasses could - easily be part of another inheritance hierarchy! (And you can still use polymorphic - queries against the <literal>Payment</literal> interface.) - </para> - - <programlisting><![CDATA[<class name="CreditCardPayment" table="CREDIT_PAYMENT"> - <id name="id" type="long" column="CREDIT_PAYMENT_ID"> - <generator class="native"/> - </id> - <discriminator column="CREDIT_CARD" type="string"/> - <property name="amount" column="CREDIT_AMOUNT"/> - ... - <subclass name="MasterCardPayment" discriminator-value="MDC"/> - <subclass name="VisaPayment" discriminator-value="VISA"/> -</class> - -<class name="NonelectronicTransaction" table="NONELECTRONIC_TXN"> - <id name="id" type="long" column="TXN_ID"> - <generator class="native"/> - </id> - ... - <joined-subclass name="CashPayment" table="CASH_PAYMENT"> - <key column="PAYMENT_ID"/> - <property name="amount" column="CASH_AMOUNT"/> - ... - </joined-subclass> - <joined-subclass name="ChequePayment" table="CHEQUE_PAYMENT"> - <key column="PAYMENT_ID"/> - <property name="amount" column="CHEQUE_AMOUNT"/> - ... - </joined-subclass> -</class>]]></programlisting> - - <para> - Once again, we don't mention <literal>Payment</literal> explicitly. If we - execute a query against the <literal>Payment</literal> interface - for - example, <literal>from Payment</literal> - Hibernate - automatically returns instances of <literal>CreditCardPayment</literal> - (and its subclasses, since they also implement <literal>Payment</literal>), - <literal>CashPayment</literal> and <literal>ChequePayment</literal> but - not instances of <literal>NonelectronicTransaction</literal>. - </para> - - </sect2> - - </sect1> - - <sect1 id="inheritance-limitations"> - <title>Limitations</title> - - <para> - There are certain limitations to the "implicit polymorphism" approach to - the table per concrete-class mapping strategy. There are somewhat less - restrictive limitations to <literal>&lt;union-subclass&gt;</literal> - mappings. - </para> - - <para> - The following table shows the limitations of table per concrete-class - mappings, and of implicit polymorphism, in Hibernate. - </para> - - <table frame="topbot"> - <title>Features of inheritance mappings</title> - <tgroup cols='8' align='left' colsep='1' rowsep='1'> - <colspec colname='c1' colwidth="1*"/> - <colspec colname='c2' colwidth="1*"/> - <colspec colname='c3' colwidth="1*"/> - <colspec colname='c4' colwidth="1*"/> - <colspec colname='c5' colwidth="1*"/> - <colspec colname='c6' colwidth="1*"/> - <colspec colname='c7' colwidth="1*"/> - <colspec colname='c8' colwidth="1*"/> - <thead> - <row> - <entry>Inheritance strategy</entry> - <entry>Polymorphic many-to-one</entry> - <entry>Polymorphic one-to-one</entry> - <entry>Polymorphic one-to-many</entry> - <entry>Polymorphic many-to-many</entry> - <entry>Polymorphic <literal>load()/get()</literal></entry> - <entry>Polymorphic queries</entry> - <entry>Polymorphic joins</entry> - <entry>Outer join fetching</entry> - </row> - </thead> - <tbody> - <row> - <entry>table per class-hierarchy</entry> - <entry><literal>&lt;many-to-one&gt;</literal></entry> - <entry><literal>&lt;one-to-one&gt;</literal></entry> - <entry><literal>&lt;one-to-many&gt;</literal></entry> - <entry><literal>&lt;many-to-many&gt;</literal></entry> - <entry><literal>s.get(Payment.class, id)</literal></entry> - <entry><literal>from Payment p</literal></entry> - <entry><literal>from Order o join o.payment p</literal></entry> - <entry><emphasis>supported</emphasis></entry> - </row> - <row> - <entry>table per subclass</entry> - <entry><literal>&lt;many-to-one&gt;</literal></entry> - <entry><literal>&lt;one-to-one&gt;</literal></entry> - <entry><literal>&lt;one-to-many&gt;</literal></entry> - <entry><literal>&lt;many-to-many&gt;</literal></entry> - <entry><literal>s.get(Payment.class, id)</literal></entry> - <entry><literal>from Payment p</literal></entry> - <entry><literal>from Order o join o.payment p</literal></entry> - <entry><emphasis>supported</emphasis></entry> - </row> - <row> - <entry>table per concrete-class (union-subclass)</entry> - <entry><literal>&lt;many-to-one&gt;</literal></entry> - <entry><literal>&lt;one-to-one&gt;</literal></entry> - <entry><literal>&lt;one-to-many&gt;</literal> (for <literal>inverse="true"</literal> only)</entry> - <entry><literal>&lt;many-to-many&gt;</literal></entry> - <entry><literal>s.get(Payment.class, id)</literal></entry> - <entry><literal>from Payment p</literal></entry> - <entry><literal>from Order o join o.payment p</literal></entry> - <entry><emphasis>supported</emphasis></entry> - </row> - <row> - <entry>table per concrete class (implicit polymorphism)</entry> - <entry><literal>&lt;any&gt;</literal></entry> - <entry><emphasis>not supported</emphasis></entry> - <entry><emphasis>not supported</emphasis></entry> - <entry><literal>&lt;many-to-any&gt;</literal></entry> - <entry><literal>s.createCriteria(Payment.class).add( Restrictions.idEq(id) ).uniqueResult()</literal></entry> - <entry><literal>from Payment p</literal></entry> - <entry><emphasis>not supported</emphasis></entry> - <entry><emphasis>not supported</emphasis></entry> - </row> - </tbody> - </tgroup> - </table> - - </sect1> - -</chapter> Deleted: core/trunk/documentation/envers/src/main/docbook/en-US/content/performance.xml =================================================================== --- core/trunk/documentation/envers/src/main/docbook/en-US/content/performance.xml 2008-11-04 17:31:01 UTC (rev 15499) +++ core/trunk/documentation/envers/src/main/docbook/en-US/content/performance.xml 2008-11-04 17:31:43 UTC (rev 15500) @@ -1,1439 +0,0 @@ -<?xml version='1.0' encoding="UTF-8"?> -<!-- - ~ Hibernate, Relational Persistence for Idiomatic Java - ~ - ~ Copyright (c) 2008, Red Hat Middleware LLC or third-party contributors as - ~ indicated by the @author tags or express copyright attribution - ~ statements applied by the authors. All third-party contributions are - ~ distributed under license by Red Hat Middleware LLC. - ~ - ~ This copyrighted material is made available to anyone wishing to use, modify, - ~ copy, or redistribute it subject to the terms and conditions of the GNU - ~ Lesser General Public License, as published by the Free Software Foundation. - ~ - ~ This program is distributed in the hope that it will be useful, - ~ but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY - ~ or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License - ~ for more details. - ~ - ~ You should have received a copy of the GNU Lesser General Public License - ~ along with this distribution; if not, write to: - ~ Free Software Foundation, Inc. - ~ 51 Franklin Street, Fifth Floor - ~ Boston, MA 02110-1301 USA - --> - -<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd"> - -<chapter id="performance"> - <title>Improving performance</title> - - <sect1 id="performance-fetching" revision="2"> - <title>Fetching strategies</title> - - <para> - A <emphasis>fetching strategy</emphasis> is the strategy Hibernate will use for - retrieving associated objects if the application needs to navigate the association. - Fetch strategies may be declared in the O/R mapping metadata, or over-ridden by a - particular HQL or <literal>Criteria</literal> query. - </para> - - <para> - Hibernate3 defines the following fetching strategies: - </para> - - <itemizedlist> - <listitem> - <para> - <emphasis>Join fetching</emphasis> - Hibernate retrieves the - associated instance or collection in the same <literal>SELECT</literal>, - using an <literal>OUTER JOIN</literal>. - </para> - </listitem> - <listitem> - <para> - <emphasis>Select fetching</emphasis> - a second <literal>SELECT</literal> - is used to retrieve the associated entity or collection. Unless - you explicitly disable lazy fetching by specifying <literal>lazy="false"</literal>, - this second select will only be executed when you actually access the - association. - </para> - </listitem> - <listitem> - <para> - <emphasis>Subselect fetching</emphasis> - a second <literal>SELECT</literal> - is used to retrieve the associated collections for all entities retrieved in a - previous query or fetch. Unless you explicitly disable lazy fetching by specifying - <literal>lazy="false"</literal>, this second select will only be executed when you - actually access the association. - </para> - </listitem> - <listitem> - <para> - <emphasis>Batch fetching</emphasis> - an optimization strategy - for select fetching - Hibernate retrieves a batch of entity instances - or collections in a single <literal>SELECT</literal>, by specifying - a list of primary keys or foreign keys. - </para> - </listitem> - </itemizedlist> - - <para> - Hibernate also distinguishes between: - </para> - - <itemizedlist> - <listitem> - <para> - <emphasis>Immediate fetching</emphasis> - an association, collection or - attribute is fetched immediately, when the owner is loaded. - </para> - </listitem> - <listitem> - <para> - <emphasis>Lazy collection fetching</emphasis> - a collection is fetched - when the application invokes an operation upon that collection. (This - is the default for collections.) - </para> - </listitem> - <listitem> - <para> - <emphasis>"Extra-lazy" collection fetching</emphasis> - individual - elements of the collection are accessed from the database as needed. - Hibernate tries not to fetch the whole collection into memory unless - absolutely needed (suitable for very large collections) - </para> - </listitem> - <listitem> - <para> - <emphasis>Proxy fetching</emphasis> - a single-valued association is - fetched when a method other than the identifier getter is invoked - upon the associated object. - </para> - </listitem> - <listitem> - <para> - <emphasis>"No-proxy" fetching</emphasis> - a single-valued association is - fetched when the instance variable is accessed. Compared to proxy fetching, - this approach is less lazy (the association is fetched even when only the - identifier is accessed) but more transparent, since no proxy is visible to - the application. This approach requires buildtime bytecode instrumentation - and is rarely necessary. - </para> - </listitem> - <listitem> - <para> - <emphasis>Lazy attribute fetching</emphasis> - an attribute or single - valued association is fetched when the instance variable is accessed. - This approach requires buildtime bytecode instrumentation and is rarely - necessary. - </para> - </listitem> - </itemizedlist> - - <para> - We have two orthogonal notions here: <emphasis>when</emphasis> is the association - fetched, and <emphasis>how</emphasis> is it fetched (what SQL is used). Don't - confuse them! We use <literal>fetch</literal> to tune performance. We may use - <literal>lazy</literal> to define a contract for what data is always available - in any detached instance of a particular class. - </para> - - <sect2 id="performance-fetching-lazy"> - <title>Working with lazy associations</title> - - <para> - By default, Hibernate3 uses lazy select fetching for collections and lazy proxy - fetching for single-valued associations. These defaults make sense for almost - all associations in almost all applications. - </para> - - <para> - <emphasis>Note:</emphasis> if you set - <literal>hibernate.default_batch_fetch_size</literal>, Hibernate will use the - batch fetch optimization for lazy fetching (this optimization may also be enabled - at a more granular level). - </para> - - <para> - However, lazy fetching poses one problem that you must be aware of. Access to a - lazy association outside of the context of an open Hibernate session will result - in an exception. For example: - </para> - - <programlisting><![CDATA[s = sessions.openSession(); -Transaction tx = s.beginTransaction(); - -User u = (User) s.createQuery("from User u where u.name=:userName") - .setString("userName", userName).uniqueResult(); -Map permissions = u.getPermissions(); - -tx.commit(); -s.close(); - -Integer accessLevel = (Integer) permissions.get("accounts"); // Error!]]></programlisting> - - <para> - Since the permissions collection was not initialized when the - <literal>Session</literal> was closed, the collection will not be able to - load its state. <emphasis>Hibernate does not support lazy initialization - for detached objects</emphasis>. The fix is to move the code that reads - from the collection to just before the transaction is committed. - </para> - - <para> - Alternatively, we could use a non-lazy collection or association, - by specifying <literal>lazy="false"</literal> for the association mapping. - However, it is intended that lazy initialization be used for almost all - collections and associations. If you define too many non-lazy associations - in your object model, Hibernate will end up needing to fetch the entire - database into memory in every transaction! - </para> - - <para> - On the other hand, we often want to choose join fetching (which is non-lazy by - nature) instead of select fetching in a particular transaction. We'll now see - how to customize the fetching strategy. In Hibernate3, the mechanisms for - choosing a fetch strategy are identical for single-valued associations and - collections. - </para> - - </sect2> - - <sect2 id="performance-fetching-custom" revision="4"> - <title>Tuning fetch strategies</title> - - <para> - Select fetching (the default) is extremely vulnerable to N+1 selects problems, - so we might want to enable join fetching in the mapping document: - </para> - - <programlisting><![CDATA[<set name="permissions" - fetch="join"> - <key column="userId"/> - <one-to-many class="Permission"/> -</set]]></programlisting> - - <programlisting><![CDATA[<many-to-one name="mother" class="Cat" fetch="join"/>]]></programlisting> - - <para> - The <literal>fetch</literal> strategy defined in the mapping document affects: - </para> - - <itemizedlist> - <listitem> - <para> - retrieval via <literal>get()</literal> or <literal>load()</literal> - </para> - </listitem> - <listitem> - <para> - retrieval that happens implicitly when an association is navigated - </para> - </listitem> - <listitem> - <para> - <literal>Criteria</literal> queries - </para> - </listitem> - <listitem> - <para> - HQL queries if <literal>subselect</literal> fetching is used - </para> - </listitem> - </itemizedlist> - - <para> - No matter what fetching strategy you use, the defined non-lazy graph is guaranteed - to be loaded into memory. Note that this might result in several immediate selects - being used to execute a particular HQL query. - </para> - - <para> - Usually, we don't use the mapping document to customize fetching. Instead, we - keep the default behavior, and override it for a particular transaction, using - <literal>left join fetch</literal> in HQL. This tells Hibernate to fetch - the association eagerly in the first select, using an outer join. In the - <literal>Criteria</literal> query API, you would use - <literal>setFetchMode(FetchMode.JOIN)</literal>. - </para> - - <para> - If you ever feel like you wish you could change the fetching strategy used by - <literal>get()</literal> or <literal>load()</literal>, simply use a - <literal>Criteria</literal> query, for example: - </para> - - <programlisting><![CDATA[User user = (User) session.createCriteria(User.class) - .setFetchMode("permissions", FetchMode.JOIN) - .add( Restrictions.idEq(userId) ) - .uniqueResult();]]></programlisting> - - <para> - (This is Hibernate's equivalent of what some ORM solutions call a "fetch plan".) - </para> - - <para> - A completely different way to avoid problems with N+1 selects is to use the - second-level cache. - </para> - - </sect2> - - <sect2 id="performance-fetching-proxies" revision="2"> - <title>Single-ended association proxies</title> - - <para> - Lazy fetching for collections is implemented using Hibernate's own implementation - of persistent collections. However, a different mechanism is needed for lazy - behavior in single-ended associations. The target entity of the association must - be proxied. Hibernate implements lazy initializing proxies for persistent objects - using runtime bytecode enhancement (via the excellent CGLIB library). - </para> - - <para> - By default, Hibernate3 generates proxies (at startup) for all persistent classes - and uses them to enable lazy fetching of <literal>many-to-one</literal> and - <literal>one-to-one</literal> associations. - </para> - - <para> - The mapping file may declare an interface to use as the proxy interface for that - class, with the <literal>proxy</literal> attribute. By default, Hibernate uses a subclass - of the class. <emphasis>Note that the proxied class must implement a default constructor - with at least package visibility. We recommend this constructor for all persistent classes!</emphasis> - </para> - - <para> - There are some gotchas to be aware of when extending this approach to polymorphic - classes, eg. - </para> - - <programlisting><![CDATA[<class name="Cat" proxy="Cat"> - ...... - <subclass name="DomesticCat"> - ..... - </subclass> -</class>]]></programlisting> - - <para> - Firstly, instances of <literal>Cat</literal> will never be castable to - <literal>DomesticCat</literal>, even if the underlying instance is an - instance of <literal>DomesticCat</literal>: - </para> - - <programlisting><![CDATA[Cat cat = (Cat) session.load(Cat.class, id); // instantiate a proxy (does not hit the db) -if ( cat.isDomesticCat() ) { // hit the db to initialize the proxy - DomesticCat dc = (DomesticCat) cat; // Error! - .... -}]]></programlisting> - - <para> - Secondly, it is possible to break proxy <literal>==</literal>. - </para> - - <programlisting><![CDATA[Cat cat = (Cat) session.load(Cat.class, id); // instantiate a Cat proxy -DomesticCat dc = - (DomesticCat) session.load(DomesticCat.class, id); // acquire new DomesticCat proxy! -System.out.println(cat==dc); // false]]></programlisting> - - <para> - However, the situation is not quite as bad as it looks. Even though we now have two references - to different proxy objects, the underlying instance will still be the same object: - </para> - - <programlisting><![CDATA[cat.setWeight(11.0); // hit the db to initialize the proxy -System.out.println( dc.getWeight() ); // 11.0]]></programlisting> - - <para> - Third, you may not use a CGLIB proxy for a <literal>final</literal> class or a class - with any <literal>final</literal> methods. - </para> - - <para> - Finally, if your persistent object acquires any resources upon instantiation (eg. in - initializers or default constructor), then those resources will also be acquired by - the proxy. The proxy class is an actual subclass of the persistent class. - </para> - - <para> - These problems are all due to fundamental limitations in Java's single inheritance model. - If you wish to avoid these problems your persistent classes must each implement an interface - that declares its business methods. You should specify these interfaces in the mapping file. eg. - </para> - - <programlisting><![CDATA[<class name="CatImpl" proxy="Cat"> - ...... - <subclass name="DomesticCatImpl" proxy="DomesticCat"> - ..... - </subclass> -</class>]]></programlisting> - - <para> - where <literal>CatImpl</literal> implements the interface <literal>Cat</literal> and - <literal>DomesticCatImpl</literal> implements the interface <literal>DomesticCat</literal>. Then - proxies for instances of <literal>Cat</literal> and <literal>DomesticCat</literal> may be returned - by <literal>load()</literal> or <literal>iterate()</literal>. (Note that <literal>list()</literal> - does not usually return proxies.) - </para> - - <programlisting><![CDATA[Cat cat = (Cat) session.load(CatImpl.class, catid); -Iterator iter = session.createQuery("from CatImpl as cat where cat.name='fritz'").iterate(); -Cat fritz = (Cat) iter.next();]]></programlisting> - - <para> - Relationships are also lazily initialized. This means you must declare any properties to be of - type <literal>Cat</literal>, not <literal>CatImpl</literal>. - </para> - - <para> - Certain operations do <emphasis>not</emphasis> require proxy initialization - </para> - - <itemizedlist spacing="compact"> - <listitem> - <para> - <literal>equals()</literal>, if the persistent class does not override - <literal>equals()</literal> - </para> - </listitem> - <listitem> - <para> - <literal>hashCode()</literal>, if the persistent class does not override - <literal>hashCode()</literal> - </para> - </listitem> - <listitem> - <para> - The identifier getter method - </para> - </listitem> - </itemizedlist> - - <para> - Hibernate will detect persistent classes that override <literal>equals()</literal> or - <literal>hashCode()</literal>. - </para> - - <para> - By choosing <literal>lazy="no-proxy"</literal> instead of the default - <literal>lazy="proxy"</literal>, we can avoid the problems associated with typecasting. - However, we will require buildtime bytecode instrumentation, and all operations - will result in immediate proxy initialization. - </para> - - </sect2> - - <sect2 id="performance-fetching-initialization" revision="1"> - <title>Initializing collections and proxies</title> - - <para> - A <literal>LazyInitializationException</literal> will be thrown by Hibernate if an uninitialized - collection or proxy is accessed outside of the scope of the <literal>Session</literal>, ie. when - the entity owning the collection or having the reference to the proxy is in the detached state. - </para> - - <para> - Sometimes we need to ensure that a proxy or collection is initialized before closing the - <literal>Session</literal>. Of course, we can alway force initialization by calling - <literal>cat.getSex()</literal> or <literal>cat.getKittens().size()</literal>, for example. - But that is confusing to readers of the code and is not convenient for generic code. - </para> - - <para> - The static methods <literal>Hibernate.initialize()</literal> and <literal>Hibernate.isInitialized()</literal> - provide the application with a convenient way of working with lazily initialized collections or - proxies. <literal>Hibernate.initialize(cat)</literal> will force the initialization of a proxy, - <literal>cat</literal>, as long as its <literal>Session</literal> is still open. - <literal>Hibernate.initialize( cat.getKittens() )</literal> has a similar effect for the collection - of kittens. - </para> - - <para> - Another option is to keep the <literal>Session</literal> open until all needed - collections and proxies have been loaded. In some application architectures, - particularly where the code that accesses data using Hibernate, and the code that - uses it are in different application layers or different physical processes, it - can be a problem to ensure that the <literal>Session</literal> is open when a - collection is initialized. There are two basic ways to deal with this issue: - </para> - - <itemizedlist> - <listitem> - <para> - In a web-based application, a servlet filter can be used to close the - <literal>Session</literal> only at the very end of a user request, once - the rendering of the view is complete (the <emphasis>Open Session in - View</emphasis> pattern). Of course, this places heavy demands on the - correctness of the exception handling of your application infrastructure. - It is vitally important that the <literal>Session</literal> is closed and the - transaction ended before returning to the user, even when an exception occurs - during rendering of the view. See the Hibernate Wiki for examples of this - "Open Session in View" pattern. - </para> - </listitem> - <listitem> - <para> - In an application with a separate business tier, the business logic must - "prepare" all collections that will be needed by the web tier before - returning. This means that the business tier should load all the data and - return all the data already initialized to the presentation/web tier that - is required for a particular use case. Usually, the application calls - <literal>Hibernate.initialize()</literal> for each collection that will - be needed in the web tier (this call must occur before the session is closed) - or retrieves the collection eagerly using a Hibernate query with a - <literal>FETCH</literal> clause or a <literal>FetchMode.JOIN</literal> in - <literal>Criteria</literal>. This is usually easier if you adopt the - <emphasis>Command</emphasis> pattern instead of a <emphasis>Session Facade</emphasis>. - </para> - </listitem> - <listitem> - <para> - You may also attach a previously loaded object to a new <literal>Session</literal> - with <literal>merge()</literal> or <literal>lock()</literal> before - accessing uninitialized collections (or other proxies). No, Hibernate does not, - and certainly <emphasis>should</emphasis> not do this automatically, since it - would introduce ad hoc transaction semantics! - </para> - </listitem> - </itemizedlist> - - <para> - Sometimes you don't want to initialize a large collection, but still need some - information about it (like its size) or a subset of the data. - </para> - - <para> - You can use a collection filter to get the size of a collection without initializing it: - </para> - - <programlisting><![CDATA[( (Integer) s.createFilter( collection, "select count(*)" ).list().get(0) ).intValue()]]></programlisting> - - <para> - The <literal>createFilter()</literal> method is also used to efficiently retrieve subsets - of a collection without needing to initialize the whole collection: - </para> - - <programlisting><![CDATA[s.createFilter( lazyCollection, "").setFirstResult(0).setMaxResults(10).list();]]></programlisting> - - </sect2> - - <sect2 id="performance-fetching-batch"> - <title>Using batch fetching</title> - - <para> - Hibernate can make efficient use of batch fetching, that is, Hibernate can load several uninitialized - proxies if one proxy is accessed (or collections. Batch fetching is an optimization of the lazy select - fetching strategy. There are two ways you can tune batch fetching: on the class and the collection level. - </para> - - <para> - Batch fetching for classes/entities is easier to understand. Imagine you have the following situation - at runtime: You have 25 <literal>Cat</literal> instances loaded in a <literal>Session</literal>, each - <literal>Cat</literal> has a reference to its <literal>owner</literal>, a <literal>Person</literal>. - The <literal>Person</literal> class is mapped with a proxy, <literal>lazy="true"</literal>. If you now - iterate through all cats and call <literal>getOwner()</literal> on each, Hibernate will by default - execute 25 <literal>SELECT</literal> statements, to retrieve the proxied owners. You can tune this - behavior by specifying a <literal>batch-size</literal> in the mapping of <literal>Person</literal>: - </para> - - <programlisting><![CDATA[<class name="Person" batch-size="10">...</class>]]></programlisting> - - <para> - Hibernate will now execute only three queries, the pattern is 10, 10, 5. - </para> - - <para> - You may also enable batch fetching of collections. For example, if each <literal>Person</literal> has - a lazy collection of <literal>Cat</literal>s, and 10 persons are currently loaded in the - <literal>Session</literal>, iterating through all persons will generate 10 <literal>SELECT</literal>s, - one for every call to <literal>getCats()</literal>. If you enable batch fetching for the - <literal>cats</literal> collection in the mapping of <literal>Person</literal>, Hibernate can pre-fetch - collections: - </para> - - <programlisting><![CDATA[<class name="Person"> - <set name="cats" batch-size="3"> - ... - </set> -</class>]]></programlisting> - - <para> - With a <literal>batch-size</literal> of 3, Hibernate will load 3, 3, 3, 1 collections in four - <literal>SELECT</literal>s. Again, the value of the attribute depends on the expected number of - uninitialized collections in a particular <literal>Session</literal>. - </para> - - <para> - Batch fetching of collections is particularly useful if you have a nested tree of items, ie. - the typical bill-of-materials pattern. (Although a <emphasis>nested set</emphasis> or a - <emphasis>materialized path</emphasis> might be a better option for read-mostly trees.) - </para> - - </sect2> - - <sect2 id="performance-fetching-subselect"> - <title>Using subselect fetching</title> - - <para> - If one lazy collection or single-valued proxy has to be fetched, Hibernate loads all of - them, re-running the original query in a subselect. This works in the same way as - batch-fetching, without the piecemeal loading. - </para> - - <!-- TODO: Write more about this --> - - </sect2> - - <sect2 id="performance-fetching-lazyproperties"> - <title>Using lazy property fetching</title> - - <para> - Hibernate3 supports the lazy fetching of individual properties. This optimization technique - is also known as <emphasis>fetch groups</emphasis>. Please note that this is mostly a - marketing feature, as in practice, optimizing row reads is much more important than - optimization of column reads. However, only loading some properties of a class might - be useful in extreme cases, when legacy tables have hundreds of columns and the data model - can not be improved. - </para> - - <para> - To enable lazy property loading, set the <literal>lazy</literal> attribute on your - particular property mappings: - </para> - - <programlisting><![CDATA[<class name="Document"> - <id name="id"> - <generator class="native"/> - </id> - <property name="name" not-null="true" length="50"/> - <property name="summary" not-null="true" length="200" lazy="true"/> - <property name="text" not-null="true" length="2000" lazy="true"/> -</class>]]></programlisting> - - <para> - Lazy property loading requires buildtime bytecode instrumentation! If your persistent - classes are not enhanced, Hibernate will silently ignore lazy property settings and - fall back to immediate fetching. - </para> - - <para> - For bytecode instrumentation, use the following Ant task: - </para> - - <programlisting><![CDATA[<target name="instrument" depends="compile"> - <taskdef name="instrument" classname="org.hibernate.tool.instrument.InstrumentTask"> - <classpath path="${jar.path}"/> - <classpath path="${classes.dir}"/> - <classpath refid="lib.class.path"/> - </taskdef> - - <instrument verbose="true"> - <fileset dir="${testclasses.dir}/org/hibernate/auction/model"> - <include name="*.class"/> - </fileset> - </instrument> -</target>]]></programlisting> - - <para> - A different (better?) way to avoid unnecessary column reads, at least for - read-only transactions is to use the projection features of HQL or Criteria - queries. This avoids the need for buildtime bytecode processing and is - certainly a preferred solution. - </para> - - <para> - You may force the usual eager fetching of properties using <literal>fetch all - properties</literal> in HQL. - </para> - - </sect2> - - </sect1> - - <sect1 id="performance-cache" revision="1"> - <title>The Second Level Cache</title> - - <para> - A Hibernate <literal>Session</literal> is a transaction-level cache of persistent data. It is - possible to configure a cluster or JVM-level (<literal>SessionFactory</literal>-level) cache on - a class-by-class and collection-by-collection basis. You may even plug in a clustered cache. Be - careful. Caches are never aware of changes made to the persistent store by another application - (though they may be configured to regularly expire cached data). - </para> - - <para revision="1"> - You have the option to tell Hibernate which caching implementation to use by - specifying the name of a class that implements <literal>org.hibernate.cache.CacheProvider</literal> - using the property <literal>hibernate.cache.provider_class</literal>. Hibernate - comes bundled with a number of built-in integrations with open-source cache providers - (listed below); additionally, you could implement your own and plug it in as - outlined above. Note that versions prior to 3.2 defaulted to use EhCache as the - default cache provider; that is no longer the case as of 3.2. - </para> - - <table frame="topbot" id="cacheproviders" revision="1"> - <title>Cache Providers</title> - <tgroup cols='5' align='left' colsep='1' rowsep='1'> - <colspec colname='c1' colwidth="1*"/> - <colspec colname='c2' colwidth="3*"/> - <colspec colname='c3' colwidth="1*"/> - <colspec colname='c4' colwidth="1*"/> - <colspec colname='c5' colwidth="1*"/> - <thead> - <row> - <entry>Cache</entry> - <entry>Provider class</entry> - <entry>Type</entry> - <entry>Cluster Safe</entry> - <entry>Query Cache Supported</entry> - </row> - </thead> - <tbody> - <row> - <entry>Hashtable (not intended for production use)</entry> - <entry><literal>org.hibernate.cache.HashtableCacheProvider</literal></entry> - <entry>memory</entry> - <entry></entry> - <entry>yes</entry> - </row> - <row> - <entry>EHCache</entry> - <entry><literal>org.hibernate.cache.EhCacheProvider</literal></entry> - <entry>memory, disk</entry> - <entry></entry> - <entry>yes</entry> - </row> - <row> - <entry>OSCache</entry> - <entry><literal>org.hibernate.cache.OSCacheProvider</literal></entry> - <entry>memory, disk</entry> - <entry></entry> - <entry>yes</entry> - </row> - <row> - <entry>SwarmCache</entry> - <entry><literal>org.hibernate.cache.SwarmCacheProvider</literal></entry> - <entry>clustered (ip multicast)</entry> - <entry>yes (clustered invalidation)</entry> - <entry></entry> - </row> - <row> - <entry>JBoss Cache 1.x</entry> - <entry><literal>org.hibernate.cache.TreeCacheProvider</literal></entry> - <entry>clustered (ip multicast), transactional</entry> - <entry>yes (replication)</entry> - <entry>yes (clock sync req.)</entry> - </row> - <row> - <entry>JBoss Cache 2</entry> - <entry><literal>org.hibernate.cache.jbc2.JBossCacheRegionFactory</literal></entry> - <entry>clustered (ip multicast), transactional</entry> - <entry>yes (replication or invalidation)</entry> - <entry>yes (clock sync req.)</entry> - </row> - </tbody> - </tgroup> - </table> - - <sect2 id="performance-cache-mapping" revision="2"> - <title>Cache mappings</title> - - <para> - The <literal>&lt;cache&gt;</literal> element of a class or collection mapping has the - following form: - </para> - - <programlistingco> - <areaspec> - <area id="cache1" coords="2 70"/> - <area id="cache2" coords="3 70"/> - <area id="cache3" coords="4 70"/> - </areaspec> - <programlisting><![CDATA[<cache - usage="transactional|read-write|nonstrict-read-write|read-only" - region="RegionName" - include="all|non-lazy" -/>]]></programlisting> - <calloutlist> - <callout arearefs="cache1"> - <para> - <literal>usage</literal> (required) specifies the caching strategy: - <literal>transactional</literal>, - <literal>read-write</literal>, - <literal>nonstrict-read-write</literal> or - <literal>read-only</literal> - </para> - </callout> - <callout arearefs="cache2"> - <para> - <literal>region</literal> (optional, defaults to the class or - collection role name) specifies the name of the second level cache - region - </para> - </callout> - <callout arearefs="cache3"> - <para> - <literal>include</literal> (optional, defaults to <literal>all</literal>) - <literal>non-lazy</literal> specifies that properties of the entity mapped - with <literal>lazy="true"</literal> may not be cached when attribute-level - lazy fetching is enabled - </para> - </callout> - </calloutlist> - </programlistingco> - - <para> - Alternatively (preferably?), you may specify <literal>&lt;class-cache&gt;</literal> and - <literal>&lt;collection-cache&gt;</literal> elements in <literal>hibernate.cfg.xml</literal>. - </para> - - <para> - The <literal>usage</literal> attribute specifies a <emphasis>cache concurrency strategy</emphasis>. - </para> - - </sect2> - - <sect2 id="performance-cache-readonly"> - <title>Strategy: read only</title> - - <para> - If your application needs to read but never modify instances of a persistent class, a - <literal>read-only</literal> cache may be used. This is the simplest and best performing - strategy. It's even perfectly safe for use in a cluster. - </para> - - <programlisting><![CDATA[<class name="eg.Immutable" mutable="false"> - <cache usage="read-only"/> - .... -</class>]]></programlisting> - - </sect2> - - - <sect2 id="performance-cache-readwrite"> - <title>Strategy: read/write</title> - - <para> - If the application needs to update data, a <literal>read-write</literal> cache might be appropriate. - This cache strategy should never be used if serializable transaction isolation level is required. - If the cache is used in a JTA environment, you must specify the property - <literal>hibernate.transaction.manager_lookup_class</literal>, naming a strategy for obtaining the - JTA <literal>TransactionManager</literal>. In other environments, you should ensure that the transaction - is completed when <literal>Session.close()</literal> or <literal>Session.disconnect()</literal> is called. - If you wish to use this strategy in a cluster, you should ensure that the underlying cache implementation - supports locking. The built-in cache providers do <emphasis>not</emphasis>. - </para> - - <programlisting><![CDATA[<class name="eg.Cat" .... > - <cache usage="read-write"/> - .... - <set name="kittens" ... > - <cache usage="read-write"/> - .... - </set> -</class>]]></programlisting> - - </sect2> - - <sect2 id="performance-cache-nonstrict"> - <title>Strategy: nonstrict read/write</title> - - <para> - If the application only occasionally needs to update data (ie. if it is extremely unlikely that two - transactions would try to update the same item simultaneously) and strict transaction isolation is - not required, a <literal>nonstrict-read-write</literal> cache might be appropriate. If the cache is - used in a JTA environment, you must specify <literal>hibernate.transaction.manager_lookup_class</literal>. - In other environments, you should ensure that the transaction is completed when - <literal>Session.close()</literal> or <literal>Session.disconnect()</literal> is called. - </para> - - </sect2> - - <sect2 id="performance-cache-transactional"> - <title>Strategy: transactional</title> - - <para> - The <literal>transactional</literal> cache strategy provides support for fully transactional cache - providers such as JBoss TreeCache. Such a cache may only be used in a JTA environment and you must - specify <literal>hibernate.transaction.manager_lookup_class</literal>. - </para> - - </sect2> - - <sect2 id="performance-cache-compat-matrix"> - <title>Cache-provider/concurrency-strategy compatibility</title> - - <important> - <para> - None of the cache providers support all of the cache concurrency strategies. - </para> - </important> - - <para> - The following table shows which providers are compatible with which concurrency strategies. - </para> - - <table frame="topbot"> - <title>Cache Concurrency Strategy Support</title> - <tgroup cols='5' align='left' colsep='1' rowsep='1'> - <colspec colname='c1' colwidth="1*"/> - <colspec colname='c2' colwidth="1*"/> - <colspec colname='c3' colwidth="1*"/> - <colspec colname='c4' colwidth="1*"/> - <colspec colname='c5' colwidth="1*"/> - <thead> - <row> - <entry>Cache</entry> - <entry>read-only</entry> - <entry>nonstrict-read-write</entry> - <entry>read-write</entry> - <entry>transactional</entry> - </row> - </thead> - <tbody> - <row> - <entry>Hashtable (not intended for production use)</entry> - <entry>yes</entry> - <entry>yes</entry> - <entry>yes</entry> - <entry></entry> - </row> - <row> - <entry>EHCache</entry> - <entry>yes</entry> - <entry>yes</entry> - <entry>yes</entry> - <entry></entry> - </row> - <row> - <entry>OSCache</entry> - <entry>yes</entry> - <entry>yes</entry> - <entry>yes</entry> - <entry></entry> - </row> - <row> - <entry>SwarmCache</entry> - <entry>yes</entry> - <entry>yes</entry> - <entry></entry> - <entry></entry> - </row> - <row> - <entry>JBoss Cache 1.x</entry> - <entry>yes</entry> - <entry></entry> - <entry></entry> - <entry>yes</entry> - </row> - <row> - <entry>JBoss Cache 2</entry> - <entry>yes</entry> - <entry></entry> - <entry></entry> - <entry>yes</entry> - </row> - </tbody> - </tgroup> - </table> - - </sect2> - - </sect1> - - <sect1 id="performance-sessioncache" revision="2"> - <title>Managing the caches</title> - - <para> - Whenever you pass an object to <literal>save()</literal>, <literal>update()</literal> - or <literal>saveOrUpdate()</literal> and whenever you retrieve an object using - <literal>load()</literal>, <literal>get()</literal>, <literal>list()</literal>, - <literal>iterate()</literal> or <literal>scroll()</literal>, that object is added - to the internal cache of the <literal>Session</literal>. - </para> - <para> - When <literal>flush()</literal> is subsequently called, the state of that object will - be synchronized with the database. If you do not want this synchronization to occur or - if you are processing a huge number of objects and need to manage memory efficiently, - the <literal>evict()</literal> method may be used to remove the object and its collections - from the first-level cache. - </para> - - <programlisting><![CDATA[ScrollableResult cats = sess.createQuery("from Cat as cat").scroll(); //a huge result set -while ( cats.next() ) { - Cat cat = (Cat) cats.get(0); - doSomethingWithACat(cat); - sess.evict(cat); -}]]></programlisting> - - <para> - The <literal>Session</literal> also provides a <literal>contains()</literal> method to determine - if an instance belongs to the session cache. - </para> - - <para> - To completely evict all objects from the session cache, call <literal>Session.clear()</literal> - </para> - - <para> - For the second-level cache, there are methods defined on <literal>SessionFactory</literal> for - evicting the cached state of an instance, entire class, collection instance or entire collection - role. - </para> - - <programlisting><![CDATA[sessionFactory.evict(Cat.class, catId); //evict a particular Cat -sessionFactory.evict(Cat.class); //evict all Cats -sessionFactory.evictCollection("Cat.kittens", catId); //evict a particular collection of kittens -sessionFactory.evictCollection("Cat.kittens"); //evict all kitten collections]]></programlisting> - - <para> - The <literal>CacheMode</literal> controls how a particular session interacts with the second-level - cache. - </para> - - <itemizedlist> - <listitem> - <para> - <literal>CacheMode.NORMAL</literal> - read items from and write items to the second-level cache - </para> - </listitem> - <listitem> - <para> - <literal>CacheMode.GET</literal> - read items from the second-level cache, but don't write to - the second-level cache except when updating data - </para> - </listitem> - <listitem> - <para> - <literal>CacheMode.PUT</literal> - write items to the second-level cache, but don't read from - the second-level cache - </para> - </listitem> - <listitem> - <para> - <literal>CacheMode.REFRESH</literal> - write items to the second-level cache, but don't read from - the second-level cache, bypass the effect of <literal>hibernate.cache.use_minimal_puts</literal>, forcing - a refresh of the second-level cache for all items read from the database - </para> - </listitem> - </itemizedlist> - - <para> - To browse the contents of a second-level or query cache region, use the <literal>Statistics</literal> - API: - </para> - - <programlisting><![CDATA[Map cacheEntries = sessionFactory.getStatistics() - .getSecondLevelCacheStatistics(regionName) - .getEntries();]]></programlisting> - - <para> - You'll need to enable statistics, and, optionally, force Hibernate to keep the cache entries in a - more human-understandable format: - </para> - - <programlisting><![CDATA[hibernate.generate_statistics true -hibernate.cache.use_structured_entries true]]></programlisting> - - </sect1> - - <sect1 id="performance-querycache" revision="1"> - <title>The Query Cache</title> - - <para> - Query result sets may also be cached. This is only useful for queries that are run - frequently with the same parameters. To use the query cache you must first enable it: - </para> - - <programlisting><![CDATA[hibernate.cache.use_query_cache true]]></programlisting> - - <para> - This setting causes the creation of two new cache regions - one holding cached query - result sets (<literal>org.hibernate.cache.StandardQueryCache</literal>), the other - holding timestamps of the most recent updates to queryable tables - (<literal>org.hibernate.cache.UpdateTimestampsCache</literal>). Note that the query - cache does not cache the state of the actual entities in the result set; it caches - only identifier values and results of value type. So the query cache should always be - used in conjunction with the second-level cache. - </para> - - <para> - Most queries do not benefit from caching, so by default queries are not cached. To - enable caching, call <literal>Query.setCacheable(true)</literal>. This call allows - the query to look for existing cache results or add its results to the cache when - it is executed. - </para> - - <para> - If you require fine-grained control over query cache expiration policies, you may - specify a named cache region for a particular query by calling - <literal>Query.setCacheRegion()</literal>. - </para> - - <programlisting><![CDATA[List blogs = sess.createQuery("from Blog blog where blog.blogger = :blogger") - .setEntity("blogger", blogger) - .setMaxResults(15) - .setCacheable(true) - .setCacheRegion("frontpages") - .list();]]></programlisting> - - <para> - If the query should force a refresh of its query cache region, you should call - <literal>Query.setCacheMode(CacheMode.REFRESH)</literal>. This is particularly useful - in cases where underlying data may have been updated via a separate process (i.e., - not modified through Hibernate) and allows the application to selectively refresh - particular query result sets. This is a more efficient alternative to eviction of - a query cache region via <literal>SessionFactory.evictQueries()</literal>. - </para> - - </sect1> - - <sect1 id="performance-collections"> - <title>Understanding Collection performance</title> - - <para> - We've already spent quite some time talking about collections. - In this section we will highlight a couple more issues about - how collections behave at runtime. - </para> - - <sect2 id="performance-collections-taxonomy"> - <title>Taxonomy</title> - - <para>Hibernate defines three basic kinds of collections:</para> - - <itemizedlist> - <listitem> - <para>collections of values</para> - </listitem> - <listitem> - <para>one to many associations</para> - </listitem> - <listitem> - <para>many to many associations</para> - </listitem> - </itemizedlist> - - <para> - This classification distinguishes the various table and foreign key - relationships but does not tell us quite everything we need to know - about the relational model. To fully understand the relational structure - and performance characteristics, we must also consider the structure of - the primary key that is used by Hibernate to update or delete collection - rows. This suggests the following classification: - </para> - - <itemizedlist> - <listitem> - <para>indexed collections</para> - </listitem> - <listitem> - <para>sets</para> - </listitem> - <listitem> - <para>bags</para> - </listitem> - </itemizedlist> - - <para> - All indexed collections (maps, lists, arrays) have a primary key consisting - of the <literal>&lt;key&gt;</literal> and <literal>&lt;index&gt;</literal> - columns. In this case collection updates are usually extremely efficient - - the primary key may be efficiently indexed and a particular row may be efficiently - located when Hibernate tries to update or delete it. - </para> - - <para> - Sets have a primary key consisting of <literal>&lt;key&gt;</literal> and element - columns. This may be less efficient for some types of collection element, particularly - composite elements or large text or binary fields; the database may not be able to index - a complex primary key as efficiently. On the other hand, for one to many or many to many - associations, particularly in the case of synthetic identifiers, it is likely to be just - as efficient. (Side-note: if you want <literal>SchemaExport</literal> to actually create - the primary key of a <literal>&lt;set&gt;</literal> for you, you must declare all columns - as <literal>not-null="true"</literal>.) - </para> - - <para> - <literal>&lt;idbag&gt;</literal> mappings define a surrogate key, so they are - always very efficient to update. In fact, they are the best case. - </para> - - <para> - Bags are the worst case. Since a bag permits duplicate element values and has no - index column, no primary key may be defined. Hibernate has no way of distinguishing - between duplicate rows. Hibernate resolves this problem by completely removing - (in a single <literal>DELETE</literal>) and recreating the collection whenever it - changes. This might be very inefficient. - </para> - - <para> - Note that for a one-to-many association, the "primary key" may not be the physical - primary key of the database table - but even in this case, the above classification - is still useful. (It still reflects how Hibernate "locates" individual rows of the - collection.) - </para> - - </sect2> - - <sect2 id="performance-collections-mostefficientupdate"> - <title>Lists, maps, idbags and sets are the most efficient collections to update</title> - - <para> - From the discussion above, it should be clear that indexed collections - and (usually) sets allow the most efficient operation in terms of adding, - removing and updating elements. - </para> - - <para> - There is, arguably, one more advantage that indexed collections have over sets for - many to many associations or collections of values. Because of the structure of a - <literal>Set</literal>, Hibernate doesn't ever <literal>UPDATE</literal> a row when - an element is "changed". Changes to a <literal>Set</literal> always work via - <literal>INSERT</literal> and <literal>DELETE</literal> (of individual rows). Once - again, this consideration does not apply to one to many associations. - </para> - - <para> - After observing that arrays cannot be lazy, we would conclude that lists, maps and - idbags are the most performant (non-inverse) collection types, with sets not far - behind. Sets are expected to be the most common kind of collection in Hibernate - applications. This is because the "set" semantics are most natural in the relational - model. - </para> - - <para> - However, in well-designed Hibernate domain models, we usually see that most collections - are in fact one-to-many associations with <literal>inverse="true"</literal>. For these - associations, the update is handled by the many-to-one end of the association, and so - considerations of collection update performance simply do not apply. - </para> - - </sect2> - - <sect2 id="performance-collections-mostefficentinverse"> - <title>Bags and lists are the most efficient inverse collections</title> - - <para> - Just before you ditch bags forever, there is a particular case in which bags (and also lists) - are much more performant than sets. For a collection with <literal>inverse="true"</literal> - (the standard bidirectional one-to-many relationship idiom, for example) we can add elements - to a bag or list without needing to initialize (fetch) the bag elements! This is because - <literal>Collection.add()</literal> or <literal>Collection.addAll()</literal> must always - return true for a bag or <literal>List</literal> (unlike a <literal>Set</literal>). This can - make the following common code much faster. - </para> - - <programlisting><![CDATA[Parent p = (Parent) sess.load(Parent.class, id); -Child c = new Child(); -c.setParent(p); -p.getChildren().add(c); //no need to fetch the collection! -sess.flush();]]></programlisting> - - </sect2> - - <sect2 id="performance-collections-oneshotdelete"> - <title>One shot delete</title> - - <para> - Occasionally, deleting collection elements one by one can be extremely inefficient. Hibernate - isn't completely stupid, so it knows not to do that in the case of an newly-empty collection - (if you called <literal>list.clear()</literal>, for example). In this case, Hibernate will - issue a single <literal>DELETE</literal> and we are done! - </para> - - <para> - Suppose we add a single element to a collection of size twenty and then remove two elements. - Hibernate will issue one <literal>INSERT</literal> statement and two <literal>DELETE</literal> - statements (unless the collection is a bag). This is certainly desirable. - </para> - - <para> - However, suppose that we remove eighteen elements, leaving two and then add thee new elements. - There are two possible ways to proceed - </para> - - <itemizedlist> - <listitem> - <para>delete eighteen rows one by one and then insert three rows</para> - </listitem> - <listitem> - <para>remove the whole collection (in one SQL <literal>DELETE</literal>) and insert - all five current elements (one by one)</para> - </listitem> - </itemizedlist> - - <para> - Hibernate isn't smart enough to know that the second option is probably quicker in this case. - (And it would probably be undesirable for Hibernate to be that smart; such behaviour might - confuse database triggers, etc.) - </para> - - <para> - Fortunately, you can force this behaviour (ie. the second strategy) at any time by discarding - (ie. dereferencing) the original collection and returning a newly instantiated collection with - all the current elements. This can be very useful and powerful from time to time. - </para> - - <para> - Of course, one-shot-delete does not apply to collections mapped <literal>inverse="true"</literal>. - </para> - - </sect2> - - </sect1> - - <sect1 id="performance-monitoring" revision="1"> - <title>Monitoring performance</title> - - <para> - Optimization is not much use without monitoring and access to performance numbers. - Hibernate provides a full range of figures about its internal operations. - Statistics in Hibernate are available per <literal>SessionFactory</literal>. - </para> - - <sect2 id="performance-monitoring-sf" revision="2"> - <title>Monitoring a SessionFactory</title> - - <para> - You can access <literal>SessionFactory</literal> metrics in two ways. - Your first option is to call <literal>sessionFactory.getStatistics()</literal> and - read or display the <literal>Statistics</literal> yourself. - </para> - - <para> - Hibernate can also use JMX to publish metrics if you enable the - <literal>StatisticsService</literal> MBean. You may enable a single MBean for all your - <literal>SessionFactory</literal> or one per factory. See the following code for - minimalistic configuration examples: - </para> - - <programlisting><![CDATA[// MBean service registration for a specific SessionFactory -Hashtable tb = new Hashtable(); -tb.put("type", "statistics"); -tb.put("sessionFactory", "myFinancialApp"); -ObjectName on = new ObjectName("hibernate", tb); // MBean object name - -StatisticsService stats = new StatisticsService(); // MBean implementation -stats.setSessionFactory(sessionFactory); // Bind the stats to a SessionFactory -server.registerMBean(stats, on); // Register the Mbean on the server]]></programlisting> - - -<programlisting><![CDATA[// MBean service registration for all SessionFactory's -Hashtable tb = new Hashtable(); -tb.put("type", "statistics"); -tb.put("sessionFactory", "all"); -ObjectName on = new ObjectName("hibernate", tb); // MBean object name - -StatisticsService stats = new StatisticsService(); // MBean implementation -server.registerMBean(stats, on); // Register the MBean on the server]]></programlisting> - - <para> - TODO: This doesn't make sense: In the first case, we retrieve and use the MBean directly. In the second one, we must give - the JNDI name in which the session factory is held before using it. Use - <literal>hibernateStatsBean.setSessionFactoryJNDIName("my/JNDI/Name")</literal> - </para> - <para> - You can (de)activate the monitoring for a <literal>SessionFactory</literal> - </para> - <itemizedlist> - <listitem> - <para> - at configuration time, set <literal>hibernate.generate_statistics</literal> to <literal>false</literal> - </para> - </listitem> - </itemizedlist> - <itemizedlist> - <listitem> - <para> - at runtime: <literal>sf.getStatistics().setStatisticsEnabled(true)</literal> - or <literal>hibernateStatsBean.setStatisticsEnabled(true)</literal> - </para> - </listitem> - </itemizedlist> - - <para> - Statistics can be reset programmatically using the <literal>clear()</literal> method. - A summary can be sent to a logger (info level) using the <literal>logSummary()</literal> - method. - </para> - - </sect2> - - <sect2 id="performance-monitoring-metrics" revision="1"> - <title>Metrics</title> - - <para> - Hibernate provides a number of metrics, from very basic to the specialized information - only relevant in certain scenarios. All available counters are described in the - <literal>Statistics</literal> interface API, in three categories: - </para> - <itemizedlist> - <listitem> - <para> - Metrics related to the general <literal>Session</literal> usage, such as - number of open sessions, retrieved JDBC connections, etc. - </para> - </listitem> - <listitem> - <para> - Metrics related to he entities, collections, queries, and caches as a - whole (aka global metrics), - </para> - </listitem> - <listitem> - <para> - Detailed metrics related to a particular entity, collection, query or - cache region. - </para> - </listitem> - </itemizedlist> - - <para> - For example, you can check the cache hit, miss, and put ratio of entities, collections - and queries, and the average time a query needs. Beware that the number of milliseconds - is subject to approximation in Java. Hibernate is tied to the JVM precision, on some - platforms this might even only be accurate to 10 seconds. - </para> - - <para> - Simple getters are used to access the global metrics (i.e. not tied to a particular entity, - collection, cache region, etc.). You can access the metrics of a particular entity, collection - or cache region through its name, and through its HQL or SQL representation for queries. Please - refer to the <literal>Statistics</literal>, <literal>EntityStatistics</literal>, - <literal>CollectionStatistics</literal>, <literal>SecondLevelCacheStatistics</literal>, - and <literal>QueryStatistics</literal> API Javadoc for more information. The following - code shows a simple example: - </para> - - <programlisting><![CDATA[Statistics stats = HibernateUtil.sessionFactory.getStatistics(); - -double queryCacheHitCount = stats.getQueryCacheHitCount(); -double queryCacheMissCount = stats.getQueryCacheMissCount(); -double queryCacheHitRatio = - queryCacheHitCount / (queryCacheHitCount + queryCacheMissCount); - -log.info("Query Hit ratio:" + queryCacheHitRatio); - -EntityStatistics entityStats = - stats.getEntityStatistics( Cat.class.getName() ); -long changes = - entityStats.getInsertCount() - + entityStats.getUpdateCount() - + entityStats.getDeleteCount(); -log.info(Cat.class.getName() + " changed " + changes + "times" );]]></programlisting> - - <para> - To work on all entities, collections, queries and region caches, you can retrieve - the list of names of entities, collections, queries and region caches with the - following methods: <literal>getQueries()</literal>, <literal>getEntityNames()</literal>, - <literal>getCollectionRoleNames()</literal>, and - <literal>getSecondLevelCacheRegionNames()</literal>. - </para> - - </sect2> - - </sect1> - -</chapter> Deleted: core/trunk/documentation/envers/src/main/docbook/en-US/content/persistent_classes.xml =================================================================== --- core/trunk/documentation/envers/src/main/docbook/en-US/content/persistent_classes.xml 2008-11-04 17:31:01 UTC (rev 15499) +++ core/trunk/documentation/envers/src/main/docbook/en-US/content/persistent_classes.xml 2008-11-04 17:31:43 UTC (rev 15500) @@ -1,561 +0,0 @@ -<?xml version='1.0' encoding="UTF-8"?> -<!-- - ~ Hibernate, Relational Persistence for Idiomatic Java - ~ - ~ Copyright (c) 2008, Red Hat Middleware LLC or third-party contributors as - ~ indicated by the @author tags or express copyright attribution - ~ statements applied by the authors. All third-party contributions are - ~ distributed under license by Red Hat Middleware LLC. - ~ - ~ This copyrighted material is made available to anyone wishing to use, modify, - ~ copy, or redistribute it subject to the terms and conditions of the GNU - ~ Lesser General Public License, as published by the Free Software Foundation. - ~ - ~ This program is distributed in the hope that it will be useful, - ~ but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY - ~ or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License - ~ for more details. - ~ - ~ You should have received a copy of the GNU Lesser General Public License - ~ along with this distribution; if not, write to: - ~ Free Software Foundation, Inc. - ~ 51 Franklin Street, Fifth Floor - ~ Boston, MA 02110-1301 USA - --> - -<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd"> - -<chapter id="persistent-classes" revision="2"> - <title>Persistent Classes</title> - - <para> - Persistent classes are classes in an application that implement the entities - of the business problem (e.g. Customer and Order in an E-commerce application). - Not all instances of a persistent class are considered to be in the persistent - state - an instance may instead be transient or detached. - </para> - - <para> - Hibernate works best if these classes follow some simple rules, also known - as the Plain Old Java Object (POJO) programming model. However, none of these - rules are hard requirements. Indeed, Hibernate3 assumes very little about - the nature of your persistent objects. You may express a domain model in other - ways: using trees of <literal>Map</literal> instances, for example. - </para> - - <sect1 id="persistent-classes-pojo"> - <title>A simple POJO example</title> - - <para> - Most Java applications require a persistent class representing felines. - </para> - - <programlisting><![CDATA[package eg; -import java.util.Set; -import java.util.Date; - -public class Cat { - private Long id; // identifier - - private Date birthdate; - private Color color; - private char sex; - private float weight; - private int litterId; - - private Cat mother; - private Set kittens = new HashSet(); - - private void setId(Long id) { - this.id=id; - } - public Long getId() { - return id; - } - - void setBirthdate(Date date) { - birthdate = date; - } - public Date getBirthdate() { - return birthdate; - } - - void setWeight(float weight) { - this.weight = weight; - } - public float getWeight() { - return weight; - } - - public Color getColor() { - return color; - } - void setColor(Color color) { - this.color = color; - } - - void setSex(char sex) { - this.sex=sex; - } - public char getSex() { - return sex; - } - - void setLitterId(int id) { - this.litterId = id; - } - public int getLitterId() { - return litterId; - } - - void setMother(Cat mother) { - this.mother = mother; - } - public Cat getMother() { - return mother; - } - void setKittens(Set kittens) { - this.kittens = kittens; - } - public Set getKittens() { - return kittens; - } - - // addKitten not needed by Hibernate - public void addKitten(Cat kitten) { - kitten.setMother(this); - kitten.setLitterId( kittens.size() ); - kittens.add(kitten); - } -}]]></programlisting> - - <para> - There are four main rules to follow here: - </para> - - - <sect2 id="persistent-classes-pojo-constructor" revision="1"> - <title>Implement a no-argument constructor</title> - - <para> - <literal>Cat</literal> has a no-argument constructor. All persistent classes must - have a default constructor (which may be non-public) so that Hibernate can instantiate - them using <literal>Constructor.newInstance()</literal>. We strongly recommend having a - default constructor with at least <emphasis>package</emphasis> visibility for runtime proxy - generation in Hibernate. - </para> - </sect2> - - <sect2 id="persistent-classes-pojo-identifier" revision="2"> - <title>Provide an identifier property (optional)</title> - - <para> - <literal>Cat</literal> has a property called <literal>id</literal>. This property - maps to the primary key column of a database table. The property might have been called - anything, and its type might have been any primitive type, any primitive "wrapper" - type, <literal>java.lang.String</literal> or <literal>java.util.Date</literal>. (If - your legacy database table has composite keys, you can even use a user-defined class - with properties of these types - see the section on composite identifiers later.) - </para> - - <para> - The identifier property is strictly optional. You can leave them off and let Hibernate - keep track of object identifiers internally. We do not recommend this, however. - </para> - - <para> - In fact, some functionality is available only to classes which declare an - identifier property: - </para> - - <itemizedlist spacing="compact"> - <listitem> - <para> - Transitive reattachment for detached objects (cascade update or cascade - merge) - see <xref linkend="objectstate-transitive"/> - </para> - </listitem> - <listitem> - <para> - <literal>Session.saveOrUpdate()</literal> - </para> - </listitem> - <listitem> - <para> - <literal>Session.merge()</literal> - </para> - </listitem> - </itemizedlist> - - <para> - We recommend you declare consistently-named identifier properties on persistent - classes. We further recommend that you use a nullable (ie. non-primitive) type. - </para> - </sect2> - - <sect2 id="persistent-classes-pojo-final"> - <title>Prefer non-final classes (optional)</title> - <para> - A central feature of Hibernate, <emphasis>proxies</emphasis>, depends upon the - persistent class being either non-final, or the implementation of an interface - that declares all public methods. - </para> - <para> - You can persist <literal>final</literal> classes that do not implement an interface - with Hibernate, but you won't be able to use proxies for lazy association fetching - - which will limit your options for performance tuning. - </para> - <para> - You should also avoid declaring <literal>public final</literal> methods on the - non-final classes. If you want to use a class with a <literal>public final</literal> - method, you must explicitly disable proxying by setting <literal>lazy="false"</literal>. - </para> - </sect2> - - <sect2 id="persistent-classes-pojo-accessors" revision="2"> - <title>Declare accessors and mutators for persistent fields (optional)</title> - - <para> - <literal>Cat</literal> declares accessor methods for all its persistent fields. - Many other ORM tools directly persist instance variables. We believe it is - better to provide an indirection between the relational schema and internal - data structures of the class. By default, Hibernate persists JavaBeans style - properties, and recognizes method names of the form <literal>getFoo</literal>, - <literal>isFoo</literal> and <literal>setFoo</literal>. You may switch to direct - field access for particular properties, if needed. - </para> - - <para> - Properties need <emphasis>not</emphasis> be declared public - Hibernate can - persist a property with a default, <literal>protected</literal> or - <literal>private</literal> get / set pair. - </para> - - </sect2> - - </sect1> - - <sect1 id="persistent-classes-inheritance"> - <title>Implementing inheritance</title> - - <para> - A subclass must also observe the first and second rules. It inherits its - identifier property from the superclass, <literal>Cat</literal>. - </para> - - <programlisting><![CDATA[package eg; - -public class DomesticCat extends Cat { - private String name; - - public String getName() { - return name; - } - protected void setName(String name) { - this.name=name; - } -}]]></programlisting> - </sect1> - - <sect1 id="persistent-classes-equalshashcode" revision="1"> - <title>Implementing <literal>equals()</literal> and <literal>hashCode()</literal></title> - - <para> - You have to override the <literal>equals()</literal> and <literal>hashCode()</literal> - methods if you - </para> - <itemizedlist spacing="compact"> - <listitem> - <para> - intend to put instances of persistent classes in a <literal>Set</literal> - (the recommended way to represent many-valued associations) - <emphasis>and</emphasis> - </para> - </listitem> - <listitem> - <para> - intend to use reattachment of detached instances - </para> - </listitem> - </itemizedlist> - - <para> - Hibernate guarantees equivalence of persistent identity (database row) and Java identity - only inside a particular session scope. So as soon as we mix instances retrieved in - different sessions, we must implement <literal>equals()</literal> and - <literal>hashCode()</literal> if we wish to have meaningful semantics for - <literal>Set</literal>s. - </para> - - <para> - The most obvious way is to implement <literal>equals()</literal>/<literal>hashCode()</literal> - by comparing the identifier value of both objects. If the value is the same, both must - be the same database row, they are therefore equal (if both are added to a <literal>Set</literal>, - we will only have one element in the <literal>Set</literal>). Unfortunately, we can't use that - approach with generated identifiers! Hibernate will only assign identifier values to objects - that are persistent, a newly created instance will not have any identifier value! Furthermore, - if an instance is unsaved and currently in a <literal>Set</literal>, saving it will assign - an identifier value to the object. If <literal>equals()</literal> and <literal>hashCode()</literal> - are based on the identifier value, the hash code would change, breaking the contract of the - <literal>Set</literal>. See the Hibernate website for a full discussion of this problem. Note - that this is not a Hibernate issue, but normal Java semantics of object identity and equality. - </para> - - <para> - We recommend implementing <literal>equals()</literal> and <literal>hashCode()</literal> - using <emphasis>Business key equality</emphasis>. Business key equality means that the - <literal>equals()</literal> method compares only the properties that form the business - key, a key that would identify our instance in the real world (a - <emphasis>natural</emphasis> candidate key): - </para> - - <programlisting><![CDATA[public class Cat { - - ... - public boolean equals(Object other) { - if (this == other) return true; - if ( !(other instanceof Cat) ) return false; - - final Cat cat = (Cat) other; - - if ( !cat.getLitterId().equals( getLitterId() ) ) return false; - if ( !cat.getMother().equals( getMother() ) ) return false; - - return true; - } - - public int hashCode() { - int result; - result = getMother().hashCode(); - result = 29 * result + getLitterId(); - return result; - } - -}]]></programlisting> - - <para> - Note that a business key does not have to be as solid as a database - primary key candidate (see <xref linkend="transactions-basics-identity"/>). - Immutable or unique properties are usually good - candidates for a business key. - </para> - - </sect1> - - <sect1 id="persistent-classes-dynamicmodels"> - <title>Dynamic models</title> - - <para> - <emphasis>Note that the following features are currently considered - experimental and may change in the near future.</emphasis> - </para> - - <para> - Persistent entities don't necessarily have to be represented as POJO classes - or as JavaBean objects at runtime. Hibernate also supports dynamic models - (using <literal>Map</literal>s of <literal>Map</literal>s at runtime) and the - representation of entities as DOM4J trees. With this approach, you don't - write persistent classes, only mapping files. - </para> - - <para> - By default, Hibernate works in normal POJO mode. You may set a default entity - representation mode for a particular <literal>SessionFactory</literal> using the - <literal>default_entity_mode</literal> configuration option (see - <xref linkend="configuration-optional-properties"/>. - </para> - - <para> - The following examples demonstrates the representation using <literal>Map</literal>s. - First, in the mapping file, an <literal>entity-name</literal> has to be declared - instead of (or in addition to) a class name: - </para> - - <programlisting><![CDATA[<hibernate-mapping> - - <class entity-name="Customer"> - - <id name="id" - type="long" - column="ID"> - <generator class="sequence"/> - </id> - - <property name="name" - column="NAME" - type="string"/> - - <property name="address" - column="ADDRESS" - type="string"/> - - <many-to-one name="organization" - column="ORGANIZATION_ID" - class="Organization"/> - - <bag name="orders" - inverse="true" - lazy="false" - cascade="all"> - <key column="CUSTOMER_ID"/> - <one-to-many class="Order"/> - </bag> - - </class> - -</hibernate-mapping>]]></programlisting> - - <para> - - Note that even though associations are declared using target class names, - the target type of an associations may also be a dynamic entity instead - of a POJO. - </para> - - <para> - After setting the default entity mode to <literal>dynamic-map</literal> - for the <literal>SessionFactory</literal>, we can at runtime work with - <literal>Map</literal>s of <literal>Map</literal>s: - </para> - - <programlisting><![CDATA[Session s = openSession(); -Transaction tx = s.beginTransaction(); -Session s = openSession(); - -// Create a customer -Map david = new HashMap(); -david.put("name", "David"); - -// Create an organization -Map foobar = new HashMap(); -foobar.put("name", "Foobar Inc."); - -// Link both -david.put("organization", foobar); - -// Save both -s.save("Customer", david); -s.save("Organization", foobar); - -tx.commit(); -s.close();]]></programlisting> - - <para> - The advantages of a dynamic mapping are quick turnaround time for prototyping - without the need for entity class implementation. However, you lose compile-time - type checking and will very likely deal with many exceptions at runtime. Thanks - to the Hibernate mapping, the database schema can easily be normalized and sound, - allowing to add a proper domain model implementation on top later on. - </para> - - <para> - Entity representation modes can also be set on a per <literal>Session</literal> - basis: - </para> - - <programlisting><![CDATA[Session dynamicSession = pojoSession.getSession(EntityMode.MAP); - -// Create a customer -Map david = new HashMap(); -david.put("name", "David"); -dynamicSession.save("Customer", david); -... -dynamicSession.flush(); -dynamicSession.close() -... -// Continue on pojoSession -]]></programlisting> - - - <para> - Please note that the call to <literal>getSession()</literal> using an - <literal>EntityMode</literal> is on the <literal>Session</literal> API, not the - <literal>SessionFactory</literal>. That way, the new <literal>Session</literal> - shares the underlying JDBC connection, transaction, and other context - information. This means you don't have tocall <literal>flush()</literal> - and <literal>close()</literal> on the secondary <literal>Session</literal>, and - also leave the transaction and connection handling to the primary unit of work. - </para> - - <para> - More information about the XML representation capabilities can be found - in <xref linkend="xml"/>. - </para> - - </sect1> - - <sect1 id="persistent-classes-tuplizers" revision="1"> - <title>Tuplizers</title> - - <para> - <literal>org.hibernate.tuple.Tuplizer</literal>, and its sub-interfaces, are responsible - for managing a particular representation of a piece of data, given that representation's - <literal>org.hibernate.EntityMode</literal>. If a given piece of data is thought of as - a data structure, then a tuplizer is the thing which knows how to create such a data structure - and how to extract values from and inject values into such a data structure. For example, - for the POJO entity mode, the correpsonding tuplizer knows how create the POJO through its - constructor and how to access the POJO properties using the defined property accessors. - There are two high-level types of Tuplizers, represented by the - <literal>org.hibernate.tuple.entity.EntityTuplizer</literal> and <literal>org.hibernate.tuple.component.ComponentTuplizer</literal> - interfaces. <literal>EntityTuplizer</literal>s are responsible for managing the above mentioned - contracts in regards to entities, while <literal>ComponentTuplizer</literal>s do the same for - components. - </para> - - <para> - Users may also plug in their own tuplizers. Perhaps you require that a <literal>java.util.Map</literal> - implementation other than <literal>java.util.HashMap</literal> be used while in the - dynamic-map entity-mode; or perhaps you need to define a different proxy generation strategy - than the one used by default. Both would be achieved by defining a custom tuplizer - implementation. Tuplizers definitions are attached to the entity or component mapping they - are meant to manage. Going back to the example of our customer entity: - </para> - - <programlisting><![CDATA[<hibernate-mapping> - <class entity-name="Customer"> - <!-- - Override the dynamic-map entity-mode - tuplizer for the customer entity - --> - <tuplizer entity-mode="dynamic-map" - class="CustomMapTuplizerImpl"/> - - <id name="id" type="long" column="ID"> - <generator class="sequence"/> - </id> - - <!-- other properties --> - ... - </class> -</hibernate-mapping> - - -public class CustomMapTuplizerImpl - extends org.hibernate.tuple.entity.DynamicMapEntityTuplizer { - // override the buildInstantiator() method to plug in our custom map... - protected final Instantiator buildInstantiator( - org.hibernate.mapping.PersistentClass mappingInfo) { - return new CustomMapInstantiator( mappingInfo ); - } - - private static final class CustomMapInstantiator - extends org.hibernate.tuple.DynamicMapInstantitor { - // override the generateMap() method to return our custom map... - protected final Map generateMap() { - return new CustomMap(); - } - } -}]]></programlisting> - - - </sect1> - - <sect1 id="persistent-classes-extensions"> - <title>Extentsions</title> - <para> - TODO: Document user-extension framework in the property and proxy packages - </para> - </sect1> - -</chapter> - Deleted: core/trunk/documentation/envers/src/main/docbook/en-US/content/preface.xml =================================================================== --- core/trunk/documentation/envers/src/main/docbook/en-US/content/preface.xml 2008-11-04 17:31:01 UTC (rev 15499) +++ core/trunk/documentation/envers/src/main/docbook/en-US/content/preface.xml 2008-11-04 17:31:43 UTC (rev 15500) @@ -1,132 +0,0 @@ -<?xml version='1.0' encoding="UTF-8"?> -<!-- - ~ Hibernate, Relational Persistence for Idiomatic Java - ~ - ~ Copyright (c) 2008, Red Hat Middleware LLC or third-party contributors as - ~ indicated by the @author tags or express copyright attribution - ~ statements applied by the authors. All third-party contributions are - ~ distributed under license by Red Hat Middleware LLC. - ~ - ~ This copyrighted material is made available to anyone wishing to use, modify, - ~ copy, or redistribute it subject to the terms and conditions of the GNU - ~ Lesser General Public License, as published by the Free Software Foundation. - ~ - ~ This program is distributed in the hope that it will be useful, - ~ but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY - ~ or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License - ~ for more details. - ~ - ~ You should have received a copy of the GNU Lesser General Public License - ~ along with this distribution; if not, write to: - ~ Free Software Foundation, Inc. - ~ 51 Franklin Street, Fifth Floor - ~ Boston, MA 02110-1301 USA - --> - -<!DOCTYPE preface PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd"> - -<preface id="preface"> - <title>Preface</title> - - <para> - Working with object-oriented software and a relational database can be cumbersome - and time consuming in today's enterprise environments. Hibernate is an object/relational - mapping tool for Java environments. The term object/relational mapping (ORM) refers to - the technique of mapping a data representation from an object model to a relational - data model with a SQL-based schema. - </para> - - <para> - Hibernate not only takes care of the mapping from Java classes to - database tables (and from Java data types to SQL data types), but also provides data - query and retrieval facilities and can significantly reduce development time otherwise - spent with manual data handling in SQL and JDBC. - </para> - - <para> - Hibernates goal is to relieve the developer from 95 percent of common data persistence - related programming tasks. Hibernate may not be the best solution for data-centric - applications that only use stored-procedures to implement the business logic in the - database, it is most useful with object-oriented domain models and business logic in - the Java-based middle-tier. However, Hibernate can certainly help you to remove or - encapsulate vendor-specific SQL code and will help with the common task of result set - translation from a tabular representation to a graph of objects. - </para> - - <para> - If you are new to Hibernate and Object/Relational Mapping or even Java, - please follow these steps: - </para> - - <orderedlist> - <listitem> - <para> - Read <xref linkend="tutorial"/> for a tutorial with step-by-step - instructions. The source code for the tutorial is included in the - distribution in the <literal>doc/reference/tutorial/</literal> - directory. - </para> - </listitem> - <listitem> - <para> - Read <xref linkend="architecture"/> to understand the environments where - Hibernate can be used. - </para> - </listitem> - <listitem> - <para> - Have a look at the <literal>eg/</literal> directory in the Hibernate - distribution, it contains a simple standalone application. Copy your - JDBC driver to the <literal>lib/</literal> directory and edit - <literal>etc/hibernate.properties</literal>, specifying correct values for - your database. From a command prompt in the distribution directory, - type <literal>ant eg</literal> (using Ant), or under Windows, type - <literal>build eg</literal>. - </para> - </listitem> - <listitem> - <para> - Use this reference documentation as your primary source of information. - Consider reading <emphasis>Java Persistence with Hibernate</emphasis> - (http://www.manning.com/bauer2) if you need more help with application - design or if you prefer a step-by-step tutorial. Also visit - http://caveatemptor.hibernate.org and download the example application - for Java Persistence with Hibernate. - </para> - </listitem> - <listitem> - <para> - FAQs are answered on the Hibernate website. - </para> - </listitem> - <listitem> - <para> - Third party demos, examples, and tutorials are linked on the Hibernate - website. - </para> - </listitem> - <listitem> - <para> - The Community Area on the Hibernate website is a good resource for - design patterns and various integration solutions (Tomcat, JBoss AS, - Struts, EJB, etc.). - </para> - </listitem> - </orderedlist> - - <para> - If you have questions, use the user forum linked on the Hibernate website. We also - provide a JIRA issue trackings system for bug reports and feature requests. If you - are interested in the development of Hibernate, join the developer mailing list. If - you are interested in translating this documentation into your language, contact us - on the developer mailing list. - </para> - - <para> - Commercial development support, production support, and training for Hibernate is - available through JBoss Inc. (see http://www.hibernate.org/SupportTraining/). - Hibernate is a Professional Open Source project and a critical component of the - JBoss Enterprise Middleware System (JEMS) suite of products. - </para> - -</preface> Deleted: core/trunk/documentation/envers/src/main/docbook/en-US/content/query_criteria.xml =================================================================== --- core/trunk/documentation/envers/src/main/docbook/en-US/content/query_criteria.xml 2008-11-04 17:31:01 UTC (rev 15499) +++ core/trunk/documentation/envers/src/main/docbook/en-US/content/query_criteria.xml 2008-11-04 17:31:43 UTC (rev 15500) @@ -1,463 +0,0 @@ -<?xml version='1.0' encoding="UTF-8"?> -<!-- - ~ Hibernate, Relational Persistence for Idiomatic Java - ~ - ~ Copyright (c) 2008, Red Hat Middleware LLC or third-party contributors as - ~ indicated by the @author tags or express copyright attribution - ~ statements applied by the authors. All third-party contributions are - ~ distributed under license by Red Hat Middleware LLC. - ~ - ~ This copyrighted material is made available to anyone wishing to use, modify, - ~ copy, or redistribute it subject to the terms and conditions of the GNU - ~ Lesser General Public License, as published by the Free Software Foundation. - ~ - ~ This program is distributed in the hope that it will be useful, - ~ but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY - ~ or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License - ~ for more details. - ~ - ~ You should have received a copy of the GNU Lesser General Public License - ~ along with this distribution; if not, write to: - ~ Free Software Foundation, Inc. - ~ 51 Franklin Street, Fifth Floor - ~ Boston, MA 02110-1301 USA - --> - -<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd"> - -<chapter id="querycriteria"> - <title>Criteria Queries</title> - - <para> - Hibernate features an intuitive, extensible criteria query API. - </para> - - <sect1 id="querycriteria-creating"> - <title>Creating a <literal>Criteria</literal> instance</title> - - <para> - The interface <literal>org.hibernate.Criteria</literal> represents a query against - a particular persistent class. The <literal>Session</literal> is a factory for - <literal>Criteria</literal> instances. - </para> - - <programlisting><![CDATA[Criteria crit = sess.createCriteria(Cat.class); -crit.setMaxResults(50); -List cats = crit.list();]]></programlisting> - - </sect1> - - <sect1 id="querycriteria-narrowing"> - <title>Narrowing the result set</title> - - <para> - An individual query criterion is an instance of the interface - <literal>org.hibernate.criterion.Criterion</literal>. The class - <literal>org.hibernate.criterion.Restrictions</literal> defines - factory methods for obtaining certain built-in - <literal>Criterion</literal> types. - </para> - - <programlisting><![CDATA[List cats = sess.createCriteria(Cat.class) - .add( Restrictions.like("name", "Fritz%") ) - .add( Restrictions.between("weight", minWeight, maxWeight) ) - .list();]]></programlisting> - - <para> - Restrictions may be grouped logically. - </para> - - <programlisting><![CDATA[List cats = sess.createCriteria(Cat.class) - .add( Restrictions.like("name", "Fritz%") ) - .add( Restrictions.or( - Restrictions.eq( "age", new Integer(0) ), - Restrictions.isNull("age") - ) ) - .list();]]></programlisting> - - <programlisting><![CDATA[List cats = sess.createCriteria(Cat.class) - .add( Restrictions.in( "name", new String[] { "Fritz", "Izi", "Pk" } ) ) - .add( Restrictions.disjunction() - .add( Restrictions.isNull("age") ) - .add( Restrictions.eq("age", new Integer(0) ) ) - .add( Restrictions.eq("age", new Integer(1) ) ) - .add( Restrictions.eq("age", new Integer(2) ) ) - ) ) - .list();]]></programlisting> - - <para> - There are quite a range of built-in criterion types (<literal>Restrictions</literal> - subclasses), but one that is especially useful lets you specify SQL directly. - </para> - - <programlisting><![CDATA[List cats = sess.createCriteria(Cat.class) - .add( Restrictions.sqlRestriction("lower({alias}.name) like lower(?)", "Fritz%", Hibernate.STRING) ) - .list();]]></programlisting> - - <para> - The <literal>{alias}</literal> placeholder with be replaced by the row alias - of the queried entity. - </para> - - <para> - An alternative approach to obtaining a criterion is to get it from a - <literal>Property</literal> instance. You can create a <literal>Property</literal> - by calling <literal>Property.forName()</literal>. - </para> - - <programlisting><![CDATA[ -Property age = Property.forName("age"); -List cats = sess.createCriteria(Cat.class) - .add( Restrictions.disjunction() - .add( age.isNull() ) - .add( age.eq( new Integer(0) ) ) - .add( age.eq( new Integer(1) ) ) - .add( age.eq( new Integer(2) ) ) - ) ) - .add( Property.forName("name").in( new String[] { "Fritz", "Izi", "Pk" } ) ) - .list();]]></programlisting> - - </sect1> - - <sect1 id="querycriteria-ordering"> - <title>Ordering the results</title> - - <para> - You may order the results using <literal>org.hibernate.criterion.Order</literal>. - </para> - - <programlisting><![CDATA[List cats = sess.createCriteria(Cat.class) - .add( Restrictions.like("name", "F%") - .addOrder( Order.asc("name") ) - .addOrder( Order.desc("age") ) - .setMaxResults(50) - .list();]]></programlisting> - - <programlisting><![CDATA[List cats = sess.createCriteria(Cat.class) - .add( Property.forName("name").like("F%") ) - .addOrder( Property.forName("name").asc() ) - .addOrder( Property.forName("age").desc() ) - .setMaxResults(50) - .list();]]></programlisting> - - </sect1> - - <sect1 id="querycriteria-associations" revision="2"> - <title>Associations</title> - - <para> - You may easily specify constraints upon related entities by navigating - associations using <literal>createCriteria()</literal>. - </para> - - <programlisting><![CDATA[List cats = sess.createCriteria(Cat.class) - .add( Restrictions.like("name", "F%") ) - .createCriteria("kittens") - .add( Restrictions.like("name", "F%") ) - .list();]]></programlisting> - - <para> - note that the second <literal>createCriteria()</literal> returns a new - instance of <literal>Criteria</literal>, which refers to the elements of - the <literal>kittens</literal> collection. - </para> - - <para> - The following, alternate form is useful in certain circumstances. - </para> - - <programlisting><![CDATA[List cats = sess.createCriteria(Cat.class) - .createAlias("kittens", "kt") - .createAlias("mate", "mt") - .add( Restrictions.eqProperty("kt.name", "mt.name") ) - .list();]]></programlisting> - - <para> - (<literal>createAlias()</literal> does not create a new instance of - <literal>Criteria</literal>.) - </para> - - <para> - Note that the kittens collections held by the <literal>Cat</literal> instances - returned by the previous two queries are <emphasis>not</emphasis> pre-filtered - by the criteria! If you wish to retrieve just the kittens that match the - criteria, you must use a <literal>ResultTransformer</literal>. - </para> - - <programlisting><![CDATA[List cats = sess.createCriteria(Cat.class) - .createCriteria("kittens", "kt") - .add( Restrictions.eq("name", "F%") ) - .setResultTransformer(Criteria.ALIAS_TO_ENTITY_MAP) - .list(); -Iterator iter = cats.iterator(); -while ( iter.hasNext() ) { - Map map = (Map) iter.next(); - Cat cat = (Cat) map.get(Criteria.ROOT_ALIAS); - Cat kitten = (Cat) map.get("kt"); -}]]></programlisting> - - </sect1> - - <sect1 id="querycriteria-dynamicfetching" revision="1"> - <title>Dynamic association fetching</title> - - <para> - You may specify association fetching semantics at runtime using - <literal>setFetchMode()</literal>. - </para> - - <programlisting><![CDATA[List cats = sess.createCriteria(Cat.class) - .add( Restrictions.like("name", "Fritz%") ) - .setFetchMode("mate", FetchMode.EAGER) - .setFetchMode("kittens", FetchMode.EAGER) - .list();]]></programlisting> - - <para> - This query will fetch both <literal>mate</literal> and <literal>kittens</literal> - by outer join. See <xref linkend="performance-fetching"/> for more information. - </para> - - </sect1> - - <sect1 id="querycriteria-examples"> - <title>Example queries</title> - - <para> - The class <literal>org.hibernate.criterion.Example</literal> allows - you to construct a query criterion from a given instance. - </para> - - <programlisting><![CDATA[Cat cat = new Cat(); -cat.setSex('F'); -cat.setColor(Color.BLACK); -List results = session.createCriteria(Cat.class) - .add( Example.create(cat) ) - .list();]]></programlisting> - - <para> - Version properties, identifiers and associations are ignored. By default, - null valued properties are excluded. - </para> - - <para> - You can adjust how the <literal>Example</literal> is applied. - </para> - - <programlisting><![CDATA[Example example = Example.create(cat) - .excludeZeroes() //exclude zero valued properties - .excludeProperty("color") //exclude the property named "color" - .ignoreCase() //perform case insensitive string comparisons - .enableLike(); //use like for string comparisons -List results = session.createCriteria(Cat.class) - .add(example) - .list();]]></programlisting> - - <para> - You can even use examples to place criteria upon associated objects. - </para> - - <programlisting><![CDATA[List results = session.createCriteria(Cat.class) - .add( Example.create(cat) ) - .createCriteria("mate") - .add( Example.create( cat.getMate() ) ) - .list();]]></programlisting> - - </sect1> - - <sect1 id="querycriteria-projection"> - <title>Projections, aggregation and grouping</title> - <para> - The class <literal>org.hibernate.criterion.Projections</literal> is a - factory for <literal>Projection</literal> instances. We apply a - projection to a query by calling <literal>setProjection()</literal>. - </para> - - <programlisting><![CDATA[List results = session.createCriteria(Cat.class) - .setProjection( Projections.rowCount() ) - .add( Restrictions.eq("color", Color.BLACK) ) - .list();]]></programlisting> - - <programlisting><![CDATA[List results = session.createCriteria(Cat.class) - .setProjection( Projections.projectionList() - .add( Projections.rowCount() ) - .add( Projections.avg("weight") ) - .add( Projections.max("weight") ) - .add( Projections.groupProperty("color") ) - ) - .list();]]></programlisting> - - <para> - There is no explicit "group by" necessary in a criteria query. Certain - projection types are defined to be <emphasis>grouping projections</emphasis>, - which also appear in the SQL <literal>group by</literal> clause. - </para> - - <para> - An alias may optionally be assigned to a projection, so that the projected value - may be referred to in restrictions or orderings. Here are two different ways to - do this: - </para> - - <programlisting><![CDATA[List results = session.createCriteria(Cat.class) - .setProjection( Projections.alias( Projections.groupProperty("color"), "colr" ) ) - .addOrder( Order.asc("colr") ) - .list();]]></programlisting> - - <programlisting><![CDATA[List results = session.createCriteria(Cat.class) - .setProjection( Projections.groupProperty("color").as("colr") ) - .addOrder( Order.asc("colr") ) - .list();]]></programlisting> - - <para> - The <literal>alias()</literal> and <literal>as()</literal> methods simply wrap a - projection instance in another, aliased, instance of <literal>Projection</literal>. - As a shortcut, you can assign an alias when you add the projection to a - projection list: - </para> - - <programlisting><![CDATA[List results = session.createCriteria(Cat.class) - .setProjection( Projections.projectionList() - .add( Projections.rowCount(), "catCountByColor" ) - .add( Projections.avg("weight"), "avgWeight" ) - .add( Projections.max("weight"), "maxWeight" ) - .add( Projections.groupProperty("color"), "color" ) - ) - .addOrder( Order.desc("catCountByColor") ) - .addOrder( Order.desc("avgWeight") ) - .list();]]></programlisting> - - <programlisting><![CDATA[List results = session.createCriteria(Domestic.class, "cat") - .createAlias("kittens", "kit") - .setProjection( Projections.projectionList() - .add( Projections.property("cat.name"), "catName" ) - .add( Projections.property("kit.name"), "kitName" ) - ) - .addOrder( Order.asc("catName") ) - .addOrder( Order.asc("kitName") ) - .list();]]></programlisting> - - <para> - You can also use <literal>Property.forName()</literal> to express projections: - </para> - - <programlisting><![CDATA[List results = session.createCriteria(Cat.class) - .setProjection( Property.forName("name") ) - .add( Property.forName("color").eq(Color.BLACK) ) - .list();]]></programlisting> - - <programlisting><![CDATA[List results = session.createCriteria(Cat.class) - .setProjection( Projections.projectionList() - .add( Projections.rowCount().as("catCountByColor") ) - .add( Property.forName("weight").avg().as("avgWeight") ) - .add( Property.forName("weight").max().as("maxWeight") ) - .add( Property.forName("color").group().as("color" ) - ) - .addOrder( Order.desc("catCountByColor") ) - .addOrder( Order.desc("avgWeight") ) - .list();]]></programlisting> - - </sect1> - - <sect1 id="querycriteria-detachedqueries"> - <title>Detached queries and subqueries</title> - <para> - The <literal>DetachedCriteria</literal> class lets you create a query outside the scope - of a session, and then later execute it using some arbitrary <literal>Session</literal>. - </para> - - <programlisting><![CDATA[DetachedCriteria query = DetachedCriteria.forClass(Cat.class) - .add( Property.forName("sex").eq('F') ); - -Session session = ....; -Transaction txn = session.beginTransaction(); -List results = query.getExecutableCriteria(session).setMaxResults(100).list(); -txn.commit(); -session.close();]]></programlisting> - - <para> - A <literal>DetachedCriteria</literal> may also be used to express a subquery. Criterion - instances involving subqueries may be obtained via <literal>Subqueries</literal> or - <literal>Property</literal>. - </para> - - <programlisting><![CDATA[DetachedCriteria avgWeight = DetachedCriteria.forClass(Cat.class) - .setProjection( Property.forName("weight").avg() ); -session.createCriteria(Cat.class) - .add( Property.forName("weight").gt(avgWeight) ) - .list();]]></programlisting> - - <programlisting><![CDATA[DetachedCriteria weights = DetachedCriteria.forClass(Cat.class) - .setProjection( Property.forName("weight") ); -session.createCriteria(Cat.class) - .add( Subqueries.geAll("weight", weights) ) - .list();]]></programlisting> - - <para> - Even correlated subqueries are possible: - </para> - - <programlisting><![CDATA[DetachedCriteria avgWeightForSex = DetachedCriteria.forClass(Cat.class, "cat2") - .setProjection( Property.forName("weight").avg() ) - .add( Property.forName("cat2.sex").eqProperty("cat.sex") ); -session.createCriteria(Cat.class, "cat") - .add( Property.forName("weight").gt(avgWeightForSex) ) - .list();]]></programlisting> - - </sect1> - - <!--TODO: ResultSetTransformer + aliasing. AliasToBeanTransformer allow returning arbitrary - user objects - similar to setResultClass in JDO2. General use of ResultTransformer - could also be explained. --> - - <sect1 id="query-criteria-naturalid"> - <title>Queries by natural identifier</title> - - <para> - For most queries, including criteria queries, the query cache is not very efficient, - because query cache invalidation occurs too frequently. However, there is one special - kind of query where we can optimize the cache invalidation algorithm: lookups by a - constant natural key. In some applications, this kind of query occurs frequently. - The criteria API provides special provision for this use case. - </para> - - <para> - First, you should map the natural key of your entity using - <literal>&lt;natural-id&gt;</literal>, and enable use of the second-level cache. - </para> - - <programlisting><![CDATA[<class name="User"> - <cache usage="read-write"/> - <id name="id"> - <generator class="increment"/> - </id> - <natural-id> - <property name="name"/> - <property name="org"/> - </natural-id> - <property name="password"/> -</class>]]></programlisting> - - <para> - Note that this functionality is not intended for use with entities with - <emphasis>mutable</emphasis> natural keys. - </para> - - <para> - Next, enable the Hibernate query cache. - </para> - - <para> - Now, <literal>Restrictions.naturalId()</literal> allows us to make use of - the more efficient cache algorithm. - </para> - - <programlisting><![CDATA[session.createCriteria(User.class) - .add( Restrictions.naturalId() - .set("name", "gavin") - .set("org", "hb") - ).setCacheable(true) - .uniqueResult();]]></programlisting> - - </sect1> - -</chapter> Deleted: core/trunk/documentation/envers/src/main/docbook/en-US/content/query_hql.xml =================================================================== --- core/trunk/documentation/envers/src/main/docbook/en-US/content/query_hql.xml 2008-11-04 17:31:01 UTC (rev 15499) +++ core/trunk/documentation/envers/src/main/docbook/en-US/content/query_hql.xml 2008-11-04 17:31:43 UTC (rev 15500) @@ -1,1261 +0,0 @@ -<?xml version='1.0' encoding="UTF-8"?> -<!-- - ~ Hibernate, Relational Persistence for Idiomatic Java - ~ - ~ Copyright (c) 2008, Red Hat Middleware LLC or third-party contributors as - ~ indicated by the @author tags or express copyright attribution - ~ statements applied by the authors. All third-party contributions are - ~ distributed under license by Red Hat Middleware LLC. - ~ - ~ This copyrighted material is made available to anyone wishing to use, modify, - ~ copy, or redistribute it subject to the terms and conditions of the GNU - ~ Lesser General Public License, as published by the Free Software Foundation. - ~ - ~ This program is distributed in the hope that it will be useful, - ~ but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY - ~ or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License - ~ for more details. - ~ - ~ You should have received a copy of the GNU Lesser General Public License - ~ along with this distribution; if not, write to: - ~ Free Software Foundation, Inc. - ~ 51 Franklin Street, Fifth Floor - ~ Boston, MA 02110-1301 USA - --> - -<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd"> - -<chapter id="queryhql" revision="1"> - <title>HQL: The Hibernate Query Language</title> - - <para> - Hibernate is equipped with an extremely powerful query language that (quite intentionally) - looks very much like SQL. But don't be fooled by the syntax; HQL is fully object-oriented, - understanding notions like inheritence, polymorphism and association. - </para> - - <sect1 id="queryhql-casesensitivity"> - <title>Case Sensitivity</title> - - <para> - Queries are case-insensitive, except for names of Java classes and properties. - So <literal>SeLeCT</literal> is the same as - <literal>sELEct</literal> is the same as - <literal>SELECT</literal> but - <literal>org.hibernate.eg.FOO</literal> is not - <literal>org.hibernate.eg.Foo</literal> and - <literal>foo.barSet</literal> is not - <literal>foo.BARSET</literal>. - </para> - - <para> - This manual uses lowercase HQL keywords. Some users find queries with uppercase keywords - more readable, but we find this convention ugly when embedded in Java code. - </para> - - </sect1> - - <sect1 id="queryhql-from"> - <title>The from clause</title> - - <para> - The simplest possible Hibernate query is of the form: - </para> - - <programlisting><![CDATA[from eg.Cat]]></programlisting> - - <para> - which simply returns all instances of the class <literal>eg.Cat</literal>. - We don't usually need to qualify the class name, since <literal>auto-import</literal> - is the default. So we almost always just write: - </para> - - <programlisting><![CDATA[from Cat]]></programlisting> - - <para> - Most of the time, you will need to assign an <emphasis>alias</emphasis>, since - you will want to refer to the <literal>Cat</literal> in other parts of the - query. - </para> - - <programlisting><![CDATA[from Cat as cat]]></programlisting> - - <para> - This query assigns the alias <literal>cat</literal> to <literal>Cat</literal> - instances, so we could use that alias later in the query. The <literal>as</literal> - keyword is optional; we could also write: - </para> - - <programlisting><![CDATA[from Cat cat]]></programlisting> - - <para> - Multiple classes may appear, resulting in a cartesian product or "cross" join. - </para> - - <programlisting><![CDATA[from Formula, Parameter]]></programlisting> - <programlisting><![CDATA[from Formula as form, Parameter as param]]></programlisting> - - <para> - It is considered good practice to name query aliases using an initial lowercase, - consistent with Java naming standards for local variables - (eg. <literal>domesticCat</literal>). - </para> - - </sect1> - - <sect1 id="queryhql-joins" revision="2"> - <title>Associations and joins</title> - - <para> - We may also assign aliases to associated entities, or even to elements of a - collection of values, using a <literal>join</literal>. - </para> - - <programlisting><![CDATA[from Cat as cat - inner join cat.mate as mate - left outer join cat.kittens as kitten]]></programlisting> - - <programlisting><![CDATA[from Cat as cat left join cat.mate.kittens as kittens]]></programlisting> - - <programlisting><![CDATA[from Formula form full join form.parameter param]]></programlisting> - - <para> - The supported join types are borrowed from ANSI SQL - </para> - - <itemizedlist spacing="compact"> - <listitem> - <para> - <literal>inner join</literal> - </para> - </listitem> - <listitem> - <para> - <literal>left outer join</literal> - </para> - </listitem> - <listitem> - <para> - <literal>right outer join</literal> - </para> - </listitem> - <listitem> - <para> - <literal>full join</literal> (not usually useful) - </para> - </listitem> - </itemizedlist> - - <para> - The <literal>inner join</literal>, <literal>left outer join</literal> and - <literal>right outer join</literal> constructs may be abbreviated. - </para> - - <programlisting><![CDATA[from Cat as cat - join cat.mate as mate - left join cat.kittens as kitten]]></programlisting> - - <para> - You may supply extra join conditions using the HQL <literal>with</literal> - keyword. - </para> - - <programlisting><![CDATA[from Cat as cat - left join cat.kittens as kitten - with kitten.bodyWeight > 10.0]]></programlisting> - - <para> - In addition, a "fetch" join allows associations or collections of values to be - initialized along with their parent objects, using a single select. This is particularly - useful in the case of a collection. It effectively overrides the outer join and - lazy declarations of the mapping file for associations and collections. See - <xref linkend="performance-fetching"/> for more information. - </para> - - <programlisting><![CDATA[from Cat as cat - inner join fetch cat.mate - left join fetch cat.kittens]]></programlisting> - - <para> - A fetch join does not usually need to assign an alias, because the associated objects - should not be used in the <literal>where</literal> clause (or any other clause). Also, - the associated objects are not returned directly in the query results. Instead, they may - be accessed via the parent object. The only reason we might need an alias is if we are - recursively join fetching a further collection: - </para> - - <programlisting><![CDATA[from Cat as cat - inner join fetch cat.mate - left join fetch cat.kittens child - left join fetch child.kittens]]></programlisting> - - <para> - Note that the <literal>fetch</literal> construct may not be used in queries called using - <literal>iterate()</literal> (though <literal>scroll()</literal> can be used). Nor should - <literal>fetch</literal> be used together with <literal>setMaxResults()</literal> or - <literal>setFirstResult()</literal> as these operations are based on the result rows, which - usually contain duplicates for eager collection fetching, hence, the number of rows is not what - you'd expect. - Nor may <literal>fetch</literal> be used together with an ad hoc <literal>with</literal> condition. - It is possible to create a cartesian product by join fetching more than one collection in a - query, so take care in this case. Join fetching multiple collection roles also sometimes gives - unexpected results for bag mappings, so be careful about how you formulate your queries in this - case. Finally, note that <literal>full join fetch</literal> and <literal>right join fetch</literal> - are not meaningful. - </para> - - <para> - If you are using property-level lazy fetching (with bytecode instrumentation), it is - possible to force Hibernate to fetch the lazy properties immediately (in the first - query) using <literal>fetch all properties</literal>. - </para> - - <programlisting><![CDATA[from Document fetch all properties order by name]]></programlisting> - <programlisting><![CDATA[from Document doc fetch all properties where lower(doc.name) like '%cats%']]></programlisting> - - </sect1> - - <sect1 id="queryhql-joins-forms"> - <title>Forms of join syntax</title> - - <para> - HQL supports two forms of association joining: <literal>implicit</literal> and <literal>explicit</literal>. - </para> - - <para> - The queries shown in the previous section all use the <literal>explicit</literal> form where - the join keyword is explicitly used in the from clause. This is the recommended form. - </para> - - <para> - The <literal>implicit</literal> form does not use the join keyword. Instead, the - associations are "dereferenced" using dot-notation. <literal>implicit</literal> joins - can appear in any of the HQL clauses. <literal>implicit</literal> join result - in inner joins in the resulting SQL statement. - </para> - - <programlisting><![CDATA[from Cat as cat where cat.mate.name like '%s%']]></programlisting> - </sect1> - - <sect1 id="queryhql-identifier-property"> - <title>Refering to identifier property</title> - - <para> - There are, generally speaking, 2 ways to refer to an entity's identifier property: - </para> - <itemizedlist spacing="compact"> - <listitem> - <para> - The special property (lowercase) <literal>id</literal> may be used to reference the identifier - property of an entity <emphasis>provided that entity does not define a non-identifier property - named id</emphasis>. - </para> - </listitem> - <listitem> - <para> - If the entity defines a named identifier property, you may use that property name. - </para> - </listitem> - </itemizedlist> - - <para> - References to composite identifier properties follow the same naming rules. If the - entity has a non-identifier property named id, the composite identifier property can only - be referenced by its defined named; otherwise, the special <literal>id</literal> property - can be used to rerference the identifier property. - </para> - - <para> - Note: this has changed significantly starting in version 3.2.2. In previous versions, - <literal>id</literal> <emphasis>always</emphasis> referred to the identifier property no - matter what its actual name. A ramification of that decision was that non-identifier - properties named <literal>id</literal> could never be referenced in Hibernate queries. - </para> - </sect1> - - <sect1 id="queryhql-select"> - <title>The select clause</title> - - <para> - The <literal>select</literal> clause picks which objects and properties to return in - the query result set. Consider: - </para> - - <programlisting><![CDATA[select mate -from Cat as cat - inner join cat.mate as mate]]></programlisting> - - <para> - The query will select <literal>mate</literal>s of other <literal>Cat</literal>s. - Actually, you may express this query more compactly as: - </para> - - <programlisting><![CDATA[select cat.mate from Cat cat]]></programlisting> - - <para> - Queries may return properties of any value type including properties of component type: - </para> - - <programlisting><![CDATA[select cat.name from DomesticCat cat -where cat.name like 'fri%']]></programlisting> - - <programlisting><![CDATA[select cust.name.firstName from Customer as cust]]></programlisting> - - <para> - Queries may return multiple objects and/or properties as an array of type - <literal>Object[]</literal>, - </para> - - <programlisting><![CDATA[select mother, offspr, mate.name -from DomesticCat as mother - inner join mother.mate as mate - left outer join mother.kittens as offspr]]></programlisting> - - <para> - or as a <literal>List</literal>, - </para> - - <programlisting><![CDATA[select new list(mother, offspr, mate.name) -from DomesticCat as mother - inner join mother.mate as mate - left outer join mother.kittens as offspr]]></programlisting> - - <para> - or as an actual typesafe Java object, - </para> - - <programlisting><![CDATA[select new Family(mother, mate, offspr) -from DomesticCat as mother - join mother.mate as mate - left join mother.kittens as offspr]]></programlisting> - - <para> - assuming that the class <literal>Family</literal> has an appropriate constructor. - </para> - - <para> - You may assign aliases to selected expressions using <literal>as</literal>: - </para> - - <programlisting><![CDATA[select max(bodyWeight) as max, min(bodyWeight) as min, count(*) as n -from Cat cat]]></programlisting> - - <para> - This is most useful when used together with <literal>select new map</literal>: - </para> - - <programlisting><![CDATA[select new map( max(bodyWeight) as max, min(bodyWeight) as min, count(*) as n ) -from Cat cat]]></programlisting> - - <para> - This query returns a <literal>Map</literal> from aliases to selected values. - </para> - - </sect1> - - <sect1 id="queryhql-aggregation"> - <title>Aggregate functions</title> - - <para> - HQL queries may even return the results of aggregate functions on properties: - </para> - - <programlisting><![CDATA[select avg(cat.weight), sum(cat.weight), max(cat.weight), count(cat) -from Cat cat]]></programlisting> - -<!-- NO LONGER SUPPORTED - <para> - Collections may also appear inside aggregate functions in the <literal>select</literal> - clause. - </para> - - <programlisting><![CDATA[select cat, count( elements(cat.kittens) ) -from Cat cat group by cat]]></programlisting> ---> - - <para> - The supported aggregate functions are - </para> - - <itemizedlist spacing="compact"> - <listitem> - <para> - <literal>avg(...), sum(...), min(...), max(...)</literal> - </para> - </listitem> - <listitem> - <para> - <literal>count(*)</literal> - </para> - </listitem> - <listitem> - <para> - <literal>count(...), count(distinct ...), count(all...)</literal> - </para> - </listitem> - </itemizedlist> - - <para> - You may use arithmetic operators, concatenation, and recognized SQL functions - in the select clause: - </para> - - <programlisting><![CDATA[select cat.weight + sum(kitten.weight) -from Cat cat - join cat.kittens kitten -group by cat.id, cat.weight]]></programlisting> - - <programlisting><![CDATA[select firstName||' '||initial||' '||upper(lastName) from Person]]></programlisting> - - <para> - The <literal>distinct</literal> and <literal>all</literal> keywords may be used and - have the same semantics as in SQL. - </para> - - <programlisting><![CDATA[select distinct cat.name from Cat cat - -select count(distinct cat.name), count(cat) from Cat cat]]></programlisting> - - </sect1> - - <sect1 id="queryhql-polymorphism"> - <title>Polymorphic queries</title> - - <para> - A query like: - </para> - - <programlisting><![CDATA[from Cat as cat]]></programlisting> - - <para> - returns instances not only of <literal>Cat</literal>, but also of subclasses like - <literal>DomesticCat</literal>. Hibernate queries may name <emphasis>any</emphasis> Java - class or interface in the <literal>from</literal> clause. The query will return instances - of all persistent classes that extend that class or implement the interface. The following - query would return all persistent objects: - </para> - - <programlisting><![CDATA[from java.lang.Object o]]></programlisting> - - <para> - The interface <literal>Named</literal> might be implemented by various persistent - classes: - </para> - - <programlisting><![CDATA[from Named n, Named m where n.name = m.name]]></programlisting> - - <para> - Note that these last two queries will require more than one SQL <literal>SELECT</literal>. This - means that the <literal>order by</literal> clause does not correctly order the whole result set. - (It also means you can't call these queries using <literal>Query.scroll()</literal>.) - </para> - - </sect1> - - <sect1 id="queryhql-where" revision="1"> - <title>The where clause</title> - - <para> - The <literal>where</literal> clause allows you to narrow the list of instances returned. - If no alias exists, you may refer to properties by name: - </para> - - <programlisting><![CDATA[from Cat where name='Fritz']]></programlisting> - - <para> - If there is an alias, use a qualified property name: - </para> - - <programlisting><![CDATA[from Cat as cat where cat.name='Fritz']]></programlisting> - - <para> - returns instances of <literal>Cat</literal> named 'Fritz'. - </para> - - <programlisting><![CDATA[select foo -from Foo foo, Bar bar -where foo.startDate = bar.date]]></programlisting> - - <para> - will return all instances of <literal>Foo</literal> for which - there exists an instance of <literal>bar</literal> with a - <literal>date</literal> property equal to the - <literal>startDate</literal> property of the - <literal>Foo</literal>. Compound path expressions make the - <literal>where</literal> clause extremely powerful. Consider: - </para> - - <programlisting><![CDATA[from Cat cat where cat.mate.name is not null]]></programlisting> - - <para> - This query translates to an SQL query with a table (inner) join. If you were to write - something like - </para> - - <programlisting><![CDATA[from Foo foo -where foo.bar.baz.customer.address.city is not null]]></programlisting> - - <para> - you would end up with a query that would require four table joins in SQL. - </para> - - <para> - The <literal>=</literal> operator may be used to compare not only properties, but also - instances: - </para> - - <programlisting><![CDATA[from Cat cat, Cat rival where cat.mate = rival.mate]]></programlisting> - - <programlisting><![CDATA[select cat, mate -from Cat cat, Cat mate -where cat.mate = mate]]></programlisting> - - <para> - The special property (lowercase) <literal>id</literal> may be used to reference the - unique identifier of an object. See <xref linkend="queryhql-identifier-property"/> - for more information. - </para> - - <programlisting><![CDATA[from Cat as cat where cat.id = 123 - -from Cat as cat where cat.mate.id = 69]]></programlisting> - - <para> - The second query is efficient. No table join is required! - </para> - - <para> - Properties of composite identifiers may also be used. Suppose <literal>Person</literal> - has a composite identifier consisting of <literal>country</literal> and - <literal>medicareNumber</literal>. Again, see <xref linkend="queryhql-identifier-property"/> - for more information regarding referencing identifier properties. - </para> - - <programlisting><![CDATA[from bank.Person person -where person.id.country = 'AU' - and person.id.medicareNumber = 123456]]></programlisting> - - <programlisting><![CDATA[from bank.Account account -where account.owner.id.country = 'AU' - and account.owner.id.medicareNumber = 123456]]></programlisting> - - <para> - Once again, the second query requires no table join. - </para> - - <para> - Likewise, the special property <literal>class</literal> accesses the discriminator value - of an instance in the case of polymorphic persistence. A Java class name embedded in the - where clause will be translated to its discriminator value. - </para> - - <programlisting><![CDATA[from Cat cat where cat.class = DomesticCat]]></programlisting> - - <para> - You may also use components or composite user types, or properties of said - component types. See <xref linkend="queryhql-components"/> for more details. - </para> - - <para> - An "any" type has the special properties <literal>id</literal> and <literal>class</literal>, - allowing us to express a join in the following way (where <literal>AuditLog.item</literal> - is a property mapped with <literal>&lt;any&gt;</literal>). - </para> - - <programlisting><![CDATA[from AuditLog log, Payment payment -where log.item.class = 'Payment' and log.item.id = payment.id]]></programlisting> - - <para> - Notice that <literal>log.item.class</literal> and <literal>payment.class</literal> - would refer to the values of completely different database columns in the above query. - </para> - - </sect1> - - <sect1 id="queryhql-expressions"> - <title>Expressions</title> - - <para> - Expressions allowed in the <literal>where</literal> clause include - most of the kind of things you could write in SQL: - </para> - - <itemizedlist spacing="compact"> - <listitem> - <para> - mathematical operators <literal>+, -, *, /</literal> - </para> - </listitem> - <listitem> - <para> - binary comparison operators <literal>=, &gt;=, &lt;=, &lt;&gt;, !=, like</literal> - </para> - </listitem> - <listitem> - <para> - logical operations <literal>and, or, not</literal> - </para> - </listitem> - <listitem> - <para> - Parentheses <literal>( )</literal>, indicating grouping - </para> - </listitem> - <listitem> - <para> - <literal>in</literal>, - <literal>not in</literal>, - <literal>between</literal>, - <literal>is null</literal>, - <literal>is not null</literal>, - <literal>is empty</literal>, - <literal>is not empty</literal>, - <literal>member of</literal> and - <literal>not member of</literal> - </para> - </listitem> - <listitem> - <para> - "Simple" case, <literal>case ... when ... then ... else ... end</literal>, and - "searched" case, <literal>case when ... then ... else ... end</literal> - </para> - </listitem> - <listitem> - <para> - string concatenation <literal>...||...</literal> or <literal>concat(...,...)</literal> - </para> - </listitem> - <listitem> - <para> - <literal>current_date()</literal>, <literal>current_time()</literal>, - <literal>current_timestamp()</literal> - </para> - </listitem> - <listitem> - <para> - <literal>second(...)</literal>, <literal>minute(...)</literal>, - <literal>hour(...)</literal>, <literal>day(...)</literal>, - <literal>month(...)</literal>, <literal>year(...)</literal>, - </para> - </listitem> - <listitem> - <para> - Any function or operator defined by EJB-QL 3.0: <literal>substring(), trim(), - lower(), upper(), length(), locate(), abs(), sqrt(), bit_length(), mod()</literal> - </para> - </listitem> - <listitem> - <para> - <literal>coalesce()</literal> and <literal>nullif()</literal> - </para> - </listitem> - <listitem> - <para> - <literal>str()</literal> for converting numeric or temporal values to a - readable string - </para> - </listitem> - <listitem> - <para> - <literal>cast(... as ...)</literal>, where the second argument is the name of - a Hibernate type, and <literal>extract(... from ...)</literal> if ANSI - <literal>cast()</literal> and <literal>extract()</literal> is supported by - the underlying database - </para> - </listitem> - <listitem> - <para> - the HQL <literal>index()</literal> function, that applies to aliases of - a joined indexed collection - </para> - </listitem> - <listitem> - <para> - HQL functions that take collection-valued path expressions: <literal>size(), - minelement(), maxelement(), minindex(), maxindex()</literal>, along with the - special <literal>elements()</literal> and <literal>indices</literal> functions - which may be quantified using <literal>some, all, exists, any, in</literal>. - </para> - </listitem> - <listitem> - <para> - Any database-supported SQL scalar function like <literal>sign()</literal>, - <literal>trunc()</literal>, <literal>rtrim()</literal>, <literal>sin()</literal> - </para> - </listitem> - <listitem> - <para> - JDBC-style positional parameters <literal>?</literal> - </para> - </listitem> - <listitem> - <para> - named parameters <literal>:name</literal>, <literal>:start_date</literal>, <literal>:x1</literal> - </para> - </listitem> - <listitem> - <para> - SQL literals <literal>'foo'</literal>, <literal>69</literal>, <literal>6.66E+2</literal>, - <literal>'1970-01-01 10:00:01.0'</literal> - </para> - </listitem> - <listitem> - <para> - Java <literal>public static final</literal> constants <literal>eg.Color.TABBY</literal> - </para> - </listitem> - </itemizedlist> - - <para> - <literal>in</literal> and <literal>between</literal> may be used as follows: - </para> - - <programlisting><![CDATA[from DomesticCat cat where cat.name between 'A' and 'B']]></programlisting> - - <programlisting><![CDATA[from DomesticCat cat where cat.name in ( 'Foo', 'Bar', 'Baz' )]]></programlisting> - - <para> - and the negated forms may be written - </para> - - <programlisting><![CDATA[from DomesticCat cat where cat.name not between 'A' and 'B']]></programlisting> - - <programlisting><![CDATA[from DomesticCat cat where cat.name not in ( 'Foo', 'Bar', 'Baz' )]]></programlisting> - - <para> - Likewise, <literal>is null</literal> and <literal>is not null</literal> may be used to test - for null values. - </para> - - <para> - Booleans may be easily used in expressions by declaring HQL query substitutions in Hibernate - configuration: - </para> - - <programlisting><![CDATA[<property name="hibernate.query.substitutions">true 1, false 0</property>]]></programlisting> - - <para> - This will replace the keywords <literal>true</literal> and <literal>false</literal> with the - literals <literal>1</literal> and <literal>0</literal> in the translated SQL from this HQL: - </para> - - <programlisting><![CDATA[from Cat cat where cat.alive = true]]></programlisting> - - <para> - You may test the size of a collection with the special property <literal>size</literal>, or - the special <literal>size()</literal> function. - </para> - - <programlisting><![CDATA[from Cat cat where cat.kittens.size > 0]]></programlisting> - - <programlisting><![CDATA[from Cat cat where size(cat.kittens) > 0]]></programlisting> - - <para> - For indexed collections, you may refer to the minimum and maximum indices using - <literal>minindex</literal> and <literal>maxindex</literal> functions. Similarly, - you may refer to the minimum and maximum elements of a collection of basic type - using the <literal>minelement</literal> and <literal>maxelement</literal> - functions. - </para> - - <programlisting><![CDATA[from Calendar cal where maxelement(cal.holidays) > current_date]]></programlisting> - - <programlisting><![CDATA[from Order order where maxindex(order.items) > 100]]></programlisting> - - <programlisting><![CDATA[from Order order where minelement(order.items) > 10000]]></programlisting> - - <para> - The SQL functions <literal>any, some, all, exists, in</literal> are supported when passed the element - or index set of a collection (<literal>elements</literal> and <literal>indices</literal> functions) - or the result of a subquery (see below). - </para> - - <programlisting><![CDATA[select mother from Cat as mother, Cat as kit -where kit in elements(foo.kittens)]]></programlisting> - - <programlisting><![CDATA[select p from NameList list, Person p -where p.name = some elements(list.names)]]></programlisting> - - <programlisting><![CDATA[from Cat cat where exists elements(cat.kittens)]]></programlisting> - - <programlisting><![CDATA[from Player p where 3 > all elements(p.scores)]]></programlisting> - - <programlisting><![CDATA[from Show show where 'fizard' in indices(show.acts)]]></programlisting> - - <para> - Note that these constructs - <literal>size</literal>, <literal>elements</literal>, - <literal>indices</literal>, <literal>minindex</literal>, <literal>maxindex</literal>, - <literal>minelement</literal>, <literal>maxelement</literal> - may only be used in - the where clause in Hibernate3. - </para> - - <para> - Elements of indexed collections (arrays, lists, maps) may be referred to by - index (in a where clause only): - </para> - - <programlisting><![CDATA[from Order order where order.items[0].id = 1234]]></programlisting> - - <programlisting><![CDATA[select person from Person person, Calendar calendar -where calendar.holidays['national day'] = person.birthDay - and person.nationality.calendar = calendar]]></programlisting> - - <programlisting><![CDATA[select item from Item item, Order order -where order.items[ order.deliveredItemIndices[0] ] = item and order.id = 11]]></programlisting> - - <programlisting><![CDATA[select item from Item item, Order order -where order.items[ maxindex(order.items) ] = item and order.id = 11]]></programlisting> - - <para> - The expression inside <literal>[]</literal> may even be an arithmetic expression. - </para> - - <programlisting><![CDATA[select item from Item item, Order order -where order.items[ size(order.items) - 1 ] = item]]></programlisting> - - <para> - HQL also provides the built-in <literal>index()</literal> function, for elements - of a one-to-many association or collection of values. - </para> - - <programlisting><![CDATA[select item, index(item) from Order order - join order.items item -where index(item) < 5]]></programlisting> - - <para> - Scalar SQL functions supported by the underlying database may be used - </para> - - <programlisting><![CDATA[from DomesticCat cat where upper(cat.name) like 'FRI%']]></programlisting> - - <para> - If you are not yet convinced by all this, think how much longer and less readable the - following query would be in SQL: - </para> - - <programlisting><![CDATA[select cust -from Product prod, - Store store - inner join store.customers cust -where prod.name = 'widget' - and store.location.name in ( 'Melbourne', 'Sydney' ) - and prod = all elements(cust.currentOrder.lineItems)]]></programlisting> - - <para> - <emphasis>Hint:</emphasis> something like - </para> - - <programlisting><![CDATA[SELECT cust.name, cust.address, cust.phone, cust.id, cust.current_order -FROM customers cust, - stores store, - locations loc, - store_customers sc, - product prod -WHERE prod.name = 'widget' - AND store.loc_id = loc.id - AND loc.name IN ( 'Melbourne', 'Sydney' ) - AND sc.store_id = store.id - AND sc.cust_id = cust.id - AND prod.id = ALL( - SELECT item.prod_id - FROM line_items item, orders o - WHERE item.order_id = o.id - AND cust.current_order = o.id - )]]></programlisting> - - </sect1> - - <sect1 id="queryhql-ordering"> - <title>The order by clause</title> - - <para> - The list returned by a query may be ordered by any property of a returned class or components: - </para> - - <programlisting><![CDATA[from DomesticCat cat -order by cat.name asc, cat.weight desc, cat.birthdate]]></programlisting> - - <para> - The optional <literal>asc</literal> or <literal>desc</literal> indicate ascending or descending order - respectively. - </para> - </sect1> - - <sect1 id="queryhql-grouping" revision="1"> - <title>The group by clause</title> - - <para> - A query that returns aggregate values may be grouped by any property of a returned class or components: - </para> - - <programlisting><![CDATA[select cat.color, sum(cat.weight), count(cat) -from Cat cat -group by cat.color]]></programlisting> - - <programlisting><![CDATA[select foo.id, avg(name), max(name) -from Foo foo join foo.names name -group by foo.id]]></programlisting> - - <para> - A <literal>having</literal> clause is also allowed. - </para> - - <programlisting><![CDATA[select cat.color, sum(cat.weight), count(cat) -from Cat cat -group by cat.color -having cat.color in (eg.Color.TABBY, eg.Color.BLACK)]]></programlisting> - - <para> - SQL functions and aggregate functions are allowed in the <literal>having</literal> - and <literal>order by</literal> clauses, if supported by the underlying database - (eg. not in MySQL). - </para> - - <programlisting><![CDATA[select cat -from Cat cat - join cat.kittens kitten -group by cat.id, cat.name, cat.other, cat.properties -having avg(kitten.weight) > 100 -order by count(kitten) asc, sum(kitten.weight) desc]]></programlisting> - - <para> - Note that neither the <literal>group by</literal> clause nor the - <literal>order by</literal> clause may contain arithmetic expressions. - Also note that Hibernate currently does not expand a grouped entity, - so you can't write <literal>group by cat</literal> if all properties - of <literal>cat</literal> are non-aggregated. You have to list all - non-aggregated properties explicitly. - </para> - - </sect1> - - <sect1 id="queryhql-subqueries" revision="3"> - <title>Subqueries</title> - - <para> - For databases that support subselects, Hibernate supports subqueries within queries. A subquery must - be surrounded by parentheses (often by an SQL aggregate function call). Even correlated subqueries - (subqueries that refer to an alias in the outer query) are allowed. - </para> - - <programlisting><![CDATA[from Cat as fatcat -where fatcat.weight > ( - select avg(cat.weight) from DomesticCat cat -)]]></programlisting> - - <programlisting><![CDATA[from DomesticCat as cat -where cat.name = some ( - select name.nickName from Name as name -)]]></programlisting> - - <programlisting><![CDATA[from Cat as cat -where not exists ( - from Cat as mate where mate.mate = cat -)]]></programlisting> - - <programlisting><![CDATA[from DomesticCat as cat -where cat.name not in ( - select name.nickName from Name as name -)]]></programlisting> - - <programlisting><![CDATA[select cat.id, (select max(kit.weight) from cat.kitten kit) -from Cat as cat]]></programlisting> - - <para> - Note that HQL subqueries may occur only in the select or where clauses. - </para> - - <para> - Note that subqueries can also utilize <literal>row value constructor</literal> syntax. See - <xref linkend="queryhql-tuple"/> for more details. - </para> - - </sect1> - - <sect1 id="queryhql-examples"> - <title>HQL examples</title> - - <para> - Hibernate queries can be quite powerful and complex. In fact, the power of the query language - is one of Hibernate's main selling points. Here are some example queries very similar to queries - that I used on a recent project. Note that most queries you will write are much simpler than these! - </para> - - <para> - The following query returns the order id, number of items and total value of the order for all - unpaid orders for a particular customer and given minimum total value, ordering the results by - total value. In determining the prices, it uses the current catalog. The resulting SQL query, - against the <literal>ORDER</literal>, <literal>ORDER_LINE</literal>, <literal>PRODUCT</literal>, - <literal>CATALOG</literal> and <literal>PRICE</literal> tables has four inner joins and an - (uncorrelated) subselect. - </para> - - <programlisting><![CDATA[select order.id, sum(price.amount), count(item) -from Order as order - join order.lineItems as item - join item.product as product, - Catalog as catalog - join catalog.prices as price -where order.paid = false - and order.customer = :customer - and price.product = product - and catalog.effectiveDate < sysdate - and catalog.effectiveDate >= all ( - select cat.effectiveDate - from Catalog as cat - where cat.effectiveDate < sysdate - ) -group by order -having sum(price.amount) > :minAmount -order by sum(price.amount) desc]]></programlisting> - - <para> - What a monster! Actually, in real life, I'm not very keen on subqueries, so my query was - really more like this: - </para> - - <programlisting><![CDATA[select order.id, sum(price.amount), count(item) -from Order as order - join order.lineItems as item - join item.product as product, - Catalog as catalog - join catalog.prices as price -where order.paid = false - and order.customer = :customer - and price.product = product - and catalog = :currentCatalog -group by order -having sum(price.amount) > :minAmount -order by sum(price.amount) desc]]></programlisting> - - <para> - The next query counts the number of payments in each status, excluding all payments in the - <literal>AWAITING_APPROVAL</literal> status where the most recent status change was made by the - current user. It translates to an SQL query with two inner joins and a correlated subselect - against the <literal>PAYMENT</literal>, <literal>PAYMENT_STATUS</literal> and - <literal>PAYMENT_STATUS_CHANGE</literal> tables. - </para> - - <programlisting><![CDATA[select count(payment), status.name -from Payment as payment - join payment.currentStatus as status - join payment.statusChanges as statusChange -where payment.status.name <> PaymentStatus.AWAITING_APPROVAL - or ( - statusChange.timeStamp = ( - select max(change.timeStamp) - from PaymentStatusChange change - where change.payment = payment - ) - and statusChange.user <> :currentUser - ) -group by status.name, status.sortOrder -order by status.sortOrder]]></programlisting> - - <para> - If I would have mapped the <literal>statusChanges</literal> collection as a list, instead of a set, - the query would have been much simpler to write. - </para> - - <programlisting><![CDATA[select count(payment), status.name -from Payment as payment - join payment.currentStatus as status -where payment.status.name <> PaymentStatus.AWAITING_APPROVAL - or payment.statusChanges[ maxIndex(payment.statusChanges) ].user <> :currentUser -group by status.name, status.sortOrder -order by status.sortOrder]]></programlisting> - - <para> - The next query uses the MS SQL Server <literal>isNull()</literal> function to return all - the accounts and unpaid payments for the organization to which the current user belongs. - It translates to an SQL query with three inner joins, an outer join and a subselect against - the <literal>ACCOUNT</literal>, <literal>PAYMENT</literal>, <literal>PAYMENT_STATUS</literal>, - <literal>ACCOUNT_TYPE</literal>, <literal>ORGANIZATION</literal> and - <literal>ORG_USER</literal> tables. - </para> - - <programlisting><![CDATA[select account, payment -from Account as account - left outer join account.payments as payment -where :currentUser in elements(account.holder.users) - and PaymentStatus.UNPAID = isNull(payment.currentStatus.name, PaymentStatus.UNPAID) -order by account.type.sortOrder, account.accountNumber, payment.dueDate]]></programlisting> - - <para> - For some databases, we would need to do away with the (correlated) subselect. - </para> - - <programlisting><![CDATA[select account, payment -from Account as account - join account.holder.users as user - left outer join account.payments as payment -where :currentUser = user - and PaymentStatus.UNPAID = isNull(payment.currentStatus.name, PaymentStatus.UNPAID) -order by account.type.sortOrder, account.accountNumber, payment.dueDate]]></programlisting> - - </sect1> - - <sect1 id="queryhql-bulk" revision="2"> - <title>Bulk update and delete</title> - - <para> - HQL now supports <literal>update</literal>, <literal>delete</literal> and - <literal>insert ... select ...</literal> statements. - See <xref linkend="batch-direct"/> for details. - </para> - </sect1> - - <sect1 id="queryhql-tipstricks"> - <title>Tips &amp; Tricks</title> - - <para> - You can count the number of query results without actually returning them: - </para> - - <programlisting><![CDATA[( (Integer) session.createQuery("select count(*) from ....").iterate().next() ).intValue()]]></programlisting> - - <para> - To order a result by the size of a collection, use the following query: - </para> - - <programlisting><![CDATA[select usr.id, usr.name -from User as usr - left join usr.messages as msg -group by usr.id, usr.name -order by count(msg)]]></programlisting> - - <para> - If your database supports subselects, you can place a condition upon selection - size in the where clause of your query: - </para> - - <programlisting><![CDATA[from User usr where size(usr.messages) >= 1]]></programlisting> - - <para> - If your database doesn't support subselects, use the following query: - </para> - - <programlisting><![CDATA[select usr.id, usr.name -from User usr.name - join usr.messages msg -group by usr.id, usr.name -having count(msg) >= 1]]></programlisting> - - <para> - As this solution can't return a <literal>User</literal> with zero messages - because of the inner join, the following form is also useful: - </para> - - <programlisting><![CDATA[select usr.id, usr.name -from User as usr - left join usr.messages as msg -group by usr.id, usr.name -having count(msg) = 0]]></programlisting> - - <para> - Properties of a JavaBean can be bound to named query parameters: - </para> - - <programlisting><![CDATA[Query q = s.createQuery("from foo Foo as foo where foo.name=:name and foo.size=:size"); -q.setProperties(fooBean); // fooBean has getName() and getSize() -List foos = q.list();]]></programlisting> - - <para> - Collections are pageable by using the <literal>Query</literal> interface with a filter: - </para> - - <programlisting><![CDATA[Query q = s.createFilter( collection, "" ); // the trivial filter -q.setMaxResults(PAGE_SIZE); -q.setFirstResult(PAGE_SIZE * pageNumber); -List page = q.list();]]></programlisting> - - <para> - Collection elements may be ordered or grouped using a query filter: - </para> - - <programlisting><![CDATA[Collection orderedCollection = s.filter( collection, "order by this.amount" ); -Collection counts = s.filter( collection, "select this.type, count(this) group by this.type" );]]></programlisting> - - <para> - You can find the size of a collection without initializing it: - </para> - - <programlisting><![CDATA[( (Integer) session.createQuery("select count(*) from ....").iterate().next() ).intValue();]]></programlisting> - - </sect1> - - <sect1 id="queryhql-components"> - <title>Components</title> - - <para> - Components might be used in just about every way that simple value types can be used in HQL - queries. They can appear in the <literal>select</literal> clause: - </para> - - <programlisting><![CDATA[select p.name from Person p]]></programlisting> - <programlisting><![CDATA[select p.name.first from Person p]]></programlisting> - - <para> - where the Person's name property is a component. Components can also be used - in the <literal>where</literal> clause: - </para> - - <programlisting><![CDATA[from Person p where p.name = :name]]></programlisting> - <programlisting><![CDATA[from Person p where p.name.first = :firstName]]></programlisting> - - <para> - Components can also be used in the <literal>order by</literal> clause: - </para> - - <programlisting><![CDATA[from Person p order by p.name]]></programlisting> - <programlisting><![CDATA[from Person p order by p.name.first]]></programlisting> - - <para> - Another common use of components is in <link linkend="queryhql-tuple">row value constructors</link>. - </para> - </sect1> - - <sect1 id="queryhql-tuple"> - <title>Row value constructor syntax</title> - - <para> - HQL supports the use of ANSI SQL <literal>row value constructor</literal> syntax (sometimes - called <literal>tuple</literal> syntax), even though the underlying database may not support - that notion. Here we are generally referring to multi-valued comparisons, typically associated - with components. Consider an entity Person which defines a name component: - </para> - - <programlisting><![CDATA[from Person p where p.name.first='John' and p.name.last='Jingleheimer-Schmidt']]></programlisting> - - <para> - That's valid syntax, although a little verbose. It be nice to make this a bit more concise and use - <literal>row value constructor</literal> syntax: - </para> - - <programlisting><![CDATA[from Person p where p.name=('John', 'Jingleheimer-Schmidt')]]></programlisting> - - <para> - It can also be useful to specify this in the <literal>select</literal> clause: - </para> - - <programlisting><![CDATA[select p.name from Person p]]></programlisting> - - <para> - Another time using <literal>row value constructor</literal> syntax can be beneficial - is when using subqueries needing to compare against multiple values: - </para> - - <programlisting><![CDATA[from Cat as cat -where not ( cat.name, cat.color ) in ( - select cat.name, cat.color from DomesticCat cat -)]]></programlisting> - - <para> - One thing to consider when deciding if you want to use this syntax is that the query will - be dependent upon the ordering of the component sub-properties in the metadata. - </para> - - </sect1> - -</chapter> - Deleted: core/trunk/documentation/envers/src/main/docbook/en-US/content/query_sql.xml =================================================================== --- core/trunk/documentation/envers/src/main/docbook/en-US/content/query_sql.xml 2008-11-04 17:31:01 UTC (rev 15499) +++ core/trunk/documentation/envers/src/main/docbook/en-US/content/query_sql.xml 2008-11-04 17:31:43 UTC (rev 15500) @@ -1,784 +0,0 @@ -<?xml version='1.0' encoding="UTF-8"?> -<!-- - ~ Hibernate, Relational Persistence for Idiomatic Java - ~ - ~ Copyright (c) 2008, Red Hat Middleware LLC or third-party contributors as - ~ indicated by the @author tags or express copyright attribution - ~ statements applied by the authors. All third-party contributions are - ~ distributed under license by Red Hat Middleware LLC. - ~ - ~ This copyrighted material is made available to anyone wishing to use, modify, - ~ copy, or redistribute it subject to the terms and conditions of the GNU - ~ Lesser General Public License, as published by the Free Software Foundation. - ~ - ~ This program is distributed in the hope that it will be useful, - ~ but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY - ~ or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License - ~ for more details. - ~ - ~ You should have received a copy of the GNU Lesser General Public License - ~ along with this distribution; if not, write to: - ~ Free Software Foundation, Inc. - ~ 51 Franklin Street, Fifth Floor - ~ Boston, MA 02110-1301 USA - --> - -<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd"> - -<chapter id="querysql" revision="2"> - <title>Native SQL</title> - - <para>You may also express queries in the native SQL dialect of your - database. This is useful if you want to utilize database specific features - such as query hints or the <literal>CONNECT</literal> keyword in Oracle. It - also provides a clean migration path from a direct SQL/JDBC based - application to Hibernate.</para> - - <para>Hibernate3 allows you to specify handwritten SQL (including stored - procedures) for all create, update, delete, and load operations.</para> - - <sect1 id="querysql-creating" revision="4"> - <title>Using a <literal>SQLQuery</literal></title> - - <para>Execution of native SQL queries is controlled via the - <literal>SQLQuery</literal> interface, which is obtained by calling - <literal>Session.createSQLQuery()</literal>. The following describes how - to use this API for querying.</para> - - <sect2> - <title>Scalar queries</title> - - <para>The most basic SQL query is to get a list of scalars - (values).</para> - - <programlisting><![CDATA[sess.createSQLQuery("SELECT * FROM CATS").list(); -sess.createSQLQuery("SELECT ID, NAME, BIRTHDATE FROM CATS").list(); -]]></programlisting> - - <para>These will both return a List of Object arrays (Object[]) with - scalar values for each column in the CATS table. Hibernate will use - ResultSetMetadata to deduce the actual order and types of the returned - scalar values.</para> - - <para>To avoid the overhead of using - <literal>ResultSetMetadata</literal> or simply to be more explicit in - what is returned one can use <literal>addScalar()</literal>.</para> - - <programlisting><![CDATA[sess.createSQLQuery("SELECT * FROM CATS") - .addScalar("ID", Hibernate.LONG) - .addScalar("NAME", Hibernate.STRING) - .addScalar("BIRTHDATE", Hibernate.DATE) -]]></programlisting> - - <para>This query specified:</para> - - <itemizedlist> - <listitem> - <para>the SQL query string</para> - </listitem> - - <listitem> - <para>the columns and types to return</para> - </listitem> - </itemizedlist> - - <para>This will still return Object arrays, but now it will not use - <literal>ResultSetMetadata</literal> but will instead explicitly get the - ID, NAME and BIRTHDATE column as respectively a Long, String and a Short - from the underlying resultset. This also means that only these three - columns will be returned, even though the query is using - <literal>*</literal> and could return more than the three listed - columns.</para> - - <para>It is possible to leave out the type information for all or some - of the scalars.</para> - - <programlisting><![CDATA[sess.createSQLQuery("SELECT * FROM CATS") - .addScalar("ID", Hibernate.LONG) - .addScalar("NAME") - .addScalar("BIRTHDATE") -]]></programlisting> - - <para>This is essentially the same query as before, but now - <literal>ResultSetMetaData</literal> is used to decide the type of NAME - and BIRTHDATE where as the type of ID is explicitly specified.</para> - - <para>How the java.sql.Types returned from ResultSetMetaData is mapped - to Hibernate types is controlled by the Dialect. If a specific type is - not mapped or does not result in the expected type it is possible to - customize it via calls to <literal>registerHibernateType</literal> in - the Dialect.</para> - </sect2> - - <sect2> - <title>Entity queries</title> - - <para>The above queries were all about returning scalar values, - basically returning the "raw" values from the resultset. The following - shows how to get entity objects from a native sql query via - <literal>addEntity()</literal>.</para> - - <programlisting><![CDATA[sess.createSQLQuery("SELECT * FROM CATS").addEntity(Cat.class); -sess.createSQLQuery("SELECT ID, NAME, BIRTHDATE FROM CATS").addEntity(Cat.class); -]]></programlisting> - - <para>This query specified:</para> - - <itemizedlist> - <listitem> - <para>the SQL query string</para> - </listitem> - - <listitem> - <para>the entity returned by the query</para> - </listitem> - </itemizedlist> - - <para>Assuming that Cat is mapped as a class with the columns ID, NAME - and BIRTHDATE the above queries will both return a List where each - element is a Cat entity.</para> - - <para>If the entity is mapped with a <literal>many-to-one</literal> to - another entity it is required to also return this when performing the - native query, otherwise a database specific "column not found" error - will occur. The additional columns will automatically be returned when - using the * notation, but we prefer to be explicit as in the following - example for a <literal>many-to-one</literal> to a - <literal>Dog</literal>:</para> - - <programlisting><![CDATA[sess.createSQLQuery("SELECT ID, NAME, BIRTHDATE, DOG_ID FROM CATS").addEntity(Cat.class); -]]></programlisting> - - <para>This will allow cat.getDog() to function properly.</para> - </sect2> - - <sect2> - <title>Handling associations and collections</title> - - <para>It is possible to eagerly join in the <literal>Dog</literal> to - avoid the possible extra roundtrip for initializing the proxy. This is - done via the <literal>addJoin()</literal> method, which allows you to - join in an association or collection.</para> - - <programlisting><![CDATA[sess.createSQLQuery("SELECT c.ID, NAME, BIRTHDATE, DOG_ID, D_ID, D_NAME FROM CATS c, DOGS d WHERE c.DOG_ID = d.D_ID") - .addEntity("cat", Cat.class) - .addJoin("cat.dog"); -]]></programlisting> - - <para>In this example the returned <literal>Cat</literal>'s will have - their <literal>dog</literal> property fully initialized without any - extra roundtrip to the database. Notice that we added a alias name - ("cat") to be able to specify the target property path of the join. It - is possible to do the same eager joining for collections, e.g. if the - <literal>Cat</literal> had a one-to-many to <literal>Dog</literal> - instead.</para> - - <programlisting><![CDATA[sess.createSQLQuery("SELECT ID, NAME, BIRTHDATE, D_ID, D_NAME, CAT_ID FROM CATS c, DOGS d WHERE c.ID = d.CAT_ID") - .addEntity("cat", Cat.class) - .addJoin("cat.dogs"); -]]></programlisting> - - <para> - At this stage we are reaching the limits of what is possible with native queries without starting to - enhance the sql queries to make them usable in Hibernate; the problems starts to arise when returning - multiple entities of the same type or when the default alias/column names are not enough. - </para> - </sect2> - - <sect2> - <title>Returning multiple entities</title> - - <para>Until now the result set column names are assumed to be the same - as the column names specified in the mapping document. This can be - problematic for SQL queries which join multiple tables, since the same - column names may appear in more than one table.</para> - - <para>Column alias injection is needed in the following query (which - most likely will fail):</para> - - <programlisting><![CDATA[sess.createSQLQuery("SELECT c.*, m.* FROM CATS c, CATS m WHERE c.MOTHER_ID = c.ID") - .addEntity("cat", Cat.class) - .addEntity("mother", Cat.class) -]]></programlisting> - - <para>The intention for this query is to return two Cat instances per - row, a cat and its mother. This will fail since there is a conflict of - names since they are mapped to the same column names and on some - databases the returned column aliases will most likely be on the form - "c.ID", "c.NAME", etc. which are not equal to the columns specified in - the mappings ("ID" and "NAME").</para> - - <para>The following form is not vulnerable to column name - duplication:</para> - - <programlisting><![CDATA[sess.createSQLQuery("SELECT {cat.*}, {mother.*} FROM CATS c, CATS m WHERE c.MOTHER_ID = c.ID") - .addEntity("cat", Cat.class) - .addEntity("mother", Cat.class) -]]></programlisting> - - <para>This query specified:</para> - - <itemizedlist> - <listitem> - <para>the SQL query string, with placeholders for Hibernate to - inject column aliases</para> - </listitem> - - <listitem> - <para>the entities returned by the query</para> - </listitem> - </itemizedlist> - - <para>The {cat.*} and {mother.*} notation used above is a shorthand for - "all properties". Alternatively, you may list the columns explicitly, but - even in this case we let Hibernate inject the SQL column aliases for - each property. The placeholder for a column alias is just the property - name qualified by the table alias. In the following example, we retrieve - Cats and their mothers from a different table (cat_log) to the one - declared in the mapping metadata. Notice that we may even use the - property aliases in the where clause if we like.</para> - - <programlisting><![CDATA[String sql = "SELECT ID as {c.id}, NAME as {c.name}, " + - "BIRTHDATE as {c.birthDate}, MOTHER_ID as {c.mother}, {mother.*} " + - "FROM CAT_LOG c, CAT_LOG m WHERE {c.mother} = c.ID"; - -List loggedCats = sess.createSQLQuery(sql) - .addEntity("cat", Cat.class) - .addEntity("mother", Cat.class).list() -]]></programlisting> - - <sect3 id="querysql-aliasreferences" revision="2"> - <title>Alias and property references</title> - - <para>For most cases the above alias injection is needed, but for - queries relating to more complex mappings like composite properties, - inheritance discriminators, collections etc. there are some specific - aliases to use to allow Hibernate to inject the proper aliases.</para> - - <para>The following table shows the different possibilities of using - the alias injection. Note: the alias names in the result are examples, - each alias will have a unique and probably different name when - used.</para> - - <table frame="topbot" id="aliasinjection-summary"> - <title>Alias injection names</title> - - <tgroup cols="3"> - <colspec colwidth="1*" /> - - <colspec colwidth="1*" /> - - <colspec colwidth="2.5*" /> - - <thead> - <row> - <entry>Description</entry> - - <entry>Syntax</entry> - - <entry>Example</entry> - </row> - </thead> - - <tbody> - <row> - <entry>A simple property</entry> - - <entry><literal>{[aliasname].[propertyname]</literal></entry> - - <entry><literal>A_NAME as {item.name}</literal></entry> - </row> - - <row> - <entry>A composite property</entry> - - <entry><literal>{[aliasname].[componentname].[propertyname]}</literal></entry> - - <entry><literal>CURRENCY as {item.amount.currency}, VALUE as - {item.amount.value}</literal></entry> - </row> - - <row> - <entry>Discriminator of an entity</entry> - - <entry><literal>{[aliasname].class}</literal></entry> - - <entry><literal>DISC as {item.class}</literal></entry> - </row> - - <row> - <entry>All properties of an entity</entry> - - <entry><literal>{[aliasname].*}</literal></entry> - - <entry><literal>{item.*}</literal></entry> - </row> - - <row> - <entry>A collection key</entry> - - <entry><literal>{[aliasname].key}</literal></entry> - - <entry><literal>ORGID as {coll.key}</literal></entry> - </row> - - <row> - <entry>The id of an collection</entry> - - <entry><literal>{[aliasname].id}</literal></entry> - - <entry><literal>EMPID as {coll.id}</literal></entry> - </row> - - <row> - <entry>The element of an collection</entry> - - <entry><literal>{[aliasname].element}</literal></entry> - - <entry><literal>XID as {coll.element}</literal></entry> - </row> - - <row> - <entry>roperty of the element in the collection</entry> - - <entry><literal>{[aliasname].element.[propertyname]}</literal></entry> - - <entry><literal>NAME as {coll.element.name}</literal></entry> - </row> - - <row> - <entry>All properties of the element in the collection</entry> - - <entry><literal>{[aliasname].element.*}</literal></entry> - - <entry><literal>{coll.element.*}</literal></entry> - </row> - - <row> - <entry>All properties of the the collection</entry> - - <entry><literal>{[aliasname].*}</literal></entry> - - <entry><literal>{coll.*}</literal></entry> - </row> - </tbody> - </tgroup> - </table> - </sect3> - </sect2> - - <sect2> - <title>Returning non-managed entities</title> - - <para>It is possible to apply a ResultTransformer to native sql queries. Allowing it to e.g. return non-managed entities.</para> - - <programlisting><![CDATA[sess.createSQLQuery("SELECT NAME, BIRTHDATE FROM CATS") - .setResultTransformer(Transformers.aliasToBean(CatDTO.class))]]></programlisting> - - <para>This query specified:</para> - - <itemizedlist> - <listitem> - <para>the SQL query string</para> - </listitem> - - <listitem> - <para>a result transformer</para> - </listitem> - </itemizedlist> - - <para> - The above query will return a list of <literal>CatDTO</literal> which has been instantiated and injected the values of NAME and BIRTHNAME into its corresponding - properties or fields. - </para> - </sect2> - - <sect2> - <title>Handling inheritance</title> - - <para>Native sql queries which query for entities that is mapped as part - of an inheritance must include all properties for the baseclass and all - it subclasses.</para> - </sect2> - - <sect2> - <title>Parameters</title> - - <para>Native sql queries support positional as well as named - parameters:</para> - - <programlisting><![CDATA[Query query = sess.createSQLQuery("SELECT * FROM CATS WHERE NAME like ?").addEntity(Cat.class); -List pusList = query.setString(0, "Pus%").list(); - -query = sess.createSQLQuery("SELECT * FROM CATS WHERE NAME like :name").addEntity(Cat.class); -List pusList = query.setString("name", "Pus%").list(); ]]></programlisting> - </sect2> - - - - </sect1> - - <sect1 id="querysql-namedqueries" revision="3"> - <title>Named SQL queries</title> - - <para>Named SQL queries may be defined in the mapping document and called - in exactly the same way as a named HQL query. In this case, we do - <emphasis>not</emphasis> need to call - <literal>addEntity()</literal>.</para> - - <programlisting><![CDATA[<sql-query name="persons"> - <return alias="person" class="eg.Person"/> - SELECT person.NAME AS {person.name}, - person.AGE AS {person.age}, - person.SEX AS {person.sex} - FROM PERSON person - WHERE person.NAME LIKE :namePattern -</sql-query>]]></programlisting> - - <programlisting><![CDATA[List people = sess.getNamedQuery("persons") - .setString("namePattern", namePattern) - .setMaxResults(50) - .list();]]></programlisting> - - <para>The <literal>&lt;return-join&gt;</literal> and - <literal>&lt;load-collection&gt;</literal> elements are used to join - associations and define queries which initialize collections, - respectively.</para> - - <programlisting><![CDATA[<sql-query name="personsWith"> - <return alias="person" class="eg.Person"/> - <return-join alias="address" property="person.mailingAddress"/> - SELECT person.NAME AS {person.name}, - person.AGE AS {person.age}, - person.SEX AS {person.sex}, - address.STREET AS {address.street}, - address.CITY AS {address.city}, - address.STATE AS {address.state}, - address.ZIP AS {address.zip} - FROM PERSON person - JOIN ADDRESS address - ON person.ID = address.PERSON_ID AND address.TYPE='MAILING' - WHERE person.NAME LIKE :namePattern -</sql-query>]]></programlisting> - - <para>A named SQL query may return a scalar value. You must declare the - column alias and Hibernate type using the - <literal>&lt;return-scalar&gt;</literal> element:</para> - - <programlisting><![CDATA[<sql-query name="mySqlQuery"> - <return-scalar column="name" type="string"/> - <return-scalar column="age" type="long"/> - SELECT p.NAME AS name, - p.AGE AS age, - FROM PERSON p WHERE p.NAME LIKE 'Hiber%' -</sql-query>]]></programlisting> - - <para>You can externalize the resultset mapping informations in a - <literal>&lt;resultset&gt;</literal> element to either reuse them across - several named queries or through the - <literal>setResultSetMapping()</literal> API.</para> - - <programlisting><![CDATA[<resultset name="personAddress"> - <return alias="person" class="eg.Person"/> - <return-join alias="address" property="person.mailingAddress"/> -</resultset> - -<sql-query name="personsWith" resultset-ref="personAddress"> - SELECT person.NAME AS {person.name}, - person.AGE AS {person.age}, - person.SEX AS {person.sex}, - address.STREET AS {address.street}, - address.CITY AS {address.city}, - address.STATE AS {address.state}, - address.ZIP AS {address.zip} - FROM PERSON person - JOIN ADDRESS address - ON person.ID = address.PERSON_ID AND address.TYPE='MAILING' - WHERE person.NAME LIKE :namePattern -</sql-query>]]></programlisting> - - <para>You can alternatively use the resultset mapping information in your - hbm files directly in java code.</para> - - <programlisting><![CDATA[List cats = sess.createSQLQuery( - "select {cat.*}, {kitten.*} from cats cat, cats kitten where kitten.mother = cat.id" - ) - .setResultSetMapping("catAndKitten") - .list();]]></programlisting> - - <sect2 id="propertyresults"> - <title>Using return-property to explicitly specify column/alias - names</title> - - <para>With <literal>&lt;return-property&gt;</literal> you can explicitly - tell Hibernate what column aliases to use, instead of using the - <literal>{}</literal>-syntax to let Hibernate inject its own - aliases.</para> - - <programlisting><![CDATA[<sql-query name="mySqlQuery"> - <return alias="person" class="eg.Person"> - <return-property name="name" column="myName"/> - <return-property name="age" column="myAge"/> - <return-property name="sex" column="mySex"/> - </return> - SELECT person.NAME AS myName, - person.AGE AS myAge, - person.SEX AS mySex, - FROM PERSON person WHERE person.NAME LIKE :name -</sql-query> -]]></programlisting> - - <para><literal>&lt;return-property&gt;</literal> also works with - multiple columns. This solves a limitation with the - <literal>{}</literal>-syntax which can not allow fine grained control of - multi-column properties.</para> - - <programlisting><![CDATA[<sql-query name="organizationCurrentEmployments"> - <return alias="emp" class="Employment"> - <return-property name="salary"> - <return-column name="VALUE"/> - <return-column name="CURRENCY"/> - </return-property> - <return-property name="endDate" column="myEndDate"/> - </return> - SELECT EMPLOYEE AS {emp.employee}, EMPLOYER AS {emp.employer}, - STARTDATE AS {emp.startDate}, ENDDATE AS {emp.endDate}, - REGIONCODE as {emp.regionCode}, EID AS {emp.id}, VALUE, CURRENCY - FROM EMPLOYMENT - WHERE EMPLOYER = :id AND ENDDATE IS NULL - ORDER BY STARTDATE ASC -</sql-query>]]></programlisting> - - <para>Notice that in this example we used - <literal>&lt;return-property&gt;</literal> in combination with the - <literal>{}</literal>-syntax for injection. Allowing users to choose how - they want to refer column and properties.</para> - - <para>If your mapping has a discriminator you must use - <literal>&lt;return-discriminator&gt;</literal> to specify the - discriminator column.</para> - </sect2> - - <sect2 id="sp_query" revision="1"> - <title>Using stored procedures for querying</title> - - <para>Hibernate 3 introduces support for queries via stored procedures - and functions. Most of the following documentation is equivalent for - both. The stored procedure/function must return a resultset as the first - out-parameter to be able to work with Hibernate. An example of such a - stored function in Oracle 9 and higher is as follows:</para> - - <programlisting><![CDATA[CREATE OR REPLACE FUNCTION selectAllEmployments - RETURN SYS_REFCURSOR -AS - st_cursor SYS_REFCURSOR; -BEGIN - OPEN st_cursor FOR - SELECT EMPLOYEE, EMPLOYER, - STARTDATE, ENDDATE, - REGIONCODE, EID, VALUE, CURRENCY - FROM EMPLOYMENT; - RETURN st_cursor; - END;]]></programlisting> - - <para>To use this query in Hibernate you need to map it via a named - query.</para> - - <programlisting><![CDATA[<sql-query name="selectAllEmployees_SP" callable="true"> - <return alias="emp" class="Employment"> - <return-property name="employee" column="EMPLOYEE"/> - <return-property name="employer" column="EMPLOYER"/> - <return-property name="startDate" column="STARTDATE"/> - <return-property name="endDate" column="ENDDATE"/> - <return-property name="regionCode" column="REGIONCODE"/> - <return-property name="id" column="EID"/> - <return-property name="salary"> - <return-column name="VALUE"/> - <return-column name="CURRENCY"/> - </return-property> - </return> - { ? = call selectAllEmployments() } -</sql-query>]]></programlisting> - - <para>Notice stored procedures currently only return scalars and - entities. <literal>&lt;return-join&gt;</literal> and - <literal>&lt;load-collection&gt;</literal> are not supported.</para> - - <sect3 id="querysql-limits-storedprocedures" revision="1"> - <title>Rules/limitations for using stored procedures</title> - - <para>To use stored procedures with Hibernate the procedures/functions - have to follow some rules. If they do not follow those rules they are - not usable with Hibernate. If you still want to use these procedures - you have to execute them via <literal>session.connection()</literal>. - The rules are different for each database, since database vendors have - different stored procedure semantics/syntax.</para> - - <para>Stored procedure queries can't be paged with - <literal>setFirstResult()/setMaxResults()</literal>.</para> - - <para>Recommended call form is standard SQL92: <literal>{ ? = call - functionName(&lt;parameters&gt;) }</literal> or <literal>{ ? = call - procedureName(&lt;parameters&gt;}</literal>. Native call syntax is not - supported.</para> - - <para>For Oracle the following rules apply:</para> - - <itemizedlist spacing="compact"> - <listitem> - <para>A function must return a result set. The first parameter of - a procedure must be an <literal>OUT</literal> that returns a - result set. This is done by using a - <literal>SYS_REFCURSOR</literal> type in Oracle 9 or 10. In Oracle - you need to define a <literal>REF CURSOR</literal> type, see - Oracle literature.</para> - </listitem> - </itemizedlist> - - <para>For Sybase or MS SQL server the following rules apply:</para> - - <itemizedlist spacing="compact"> - <listitem> - <para>The procedure must return a result set. Note that since - these servers can/will return multiple result sets and update - counts, Hibernate will iterate the results and take the first - result that is a result set as its return value. Everything else - will be discarded.</para> - </listitem> - - <listitem> - <para>If you can enable <literal>SET NOCOUNT ON</literal> in your - procedure it will probably be more efficient, but this is not a - requirement.</para> - </listitem> - </itemizedlist> - </sect3> - </sect2> - </sect1> - - <sect1 id="querysql-cud"> - <title>Custom SQL for create, update and delete</title> - - <para>Hibernate3 can use custom SQL statements for create, update, and - delete operations. The class and collection persisters in Hibernate - already contain a set of configuration time generated strings (insertsql, - deletesql, updatesql etc.). The mapping tags - <literal>&lt;sql-insert&gt;</literal>, - <literal>&lt;sql-delete&gt;</literal>, and - <literal>&lt;sql-update&gt;</literal> override these strings:</para> - - <programlisting><![CDATA[<class name="Person"> - <id name="id"> - <generator class="increment"/> - </id> - <property name="name" not-null="true"/> - <sql-insert>INSERT INTO PERSON (NAME, ID) VALUES ( UPPER(?), ? )</sql-insert> - <sql-update>UPDATE PERSON SET NAME=UPPER(?) WHERE ID=?</sql-update> - <sql-delete>DELETE FROM PERSON WHERE ID=?</sql-delete> -</class>]]></programlisting> - - <para>The SQL is directly executed in your database, so you are free to - use any dialect you like. This will of course reduce the portability of - your mapping if you use database specific SQL.</para> - - <para>Stored procedures are supported if the <literal>callable</literal> - attribute is set:</para> - - <programlisting><![CDATA[<class name="Person"> - <id name="id"> - <generator class="increment"/> - </id> - <property name="name" not-null="true"/> - <sql-insert callable="true">{call createPerson (?, ?)}</sql-insert> - <sql-delete callable="true">{? = call deletePerson (?)}</sql-delete> - <sql-update callable="true">{? = call updatePerson (?, ?)}</sql-update> -</class>]]></programlisting> - - <para>The order of the positional parameters are currently vital, as they - must be in the same sequence as Hibernate expects them.</para> - - <para>You can see the expected order by enabling debug logging for the - <literal>org.hibernate.persister.entity</literal> level. With this level - enabled Hibernate will print out the static SQL that is used to create, - update, delete etc. entities. (To see the expected sequence, remember to - not include your custom SQL in the mapping files as that will override the - Hibernate generated static sql.)</para> - - <para>The stored procedures are in most cases (read: better do it than - not) required to return the number of rows inserted/updated/deleted, as - Hibernate has some runtime checks for the success of the statement. - Hibernate always registers the first statement parameter as a numeric - output parameter for the CUD operations:</para> - - <programlisting><![CDATA[CREATE OR REPLACE FUNCTION updatePerson (uid IN NUMBER, uname IN VARCHAR2) - RETURN NUMBER IS -BEGIN - - update PERSON - set - NAME = uname, - where - ID = uid; - - return SQL%ROWCOUNT; - -END updatePerson;]]></programlisting> - </sect1> - - <sect1 id="querysql-load"> - <title>Custom SQL for loading</title> - - <para>You may also declare your own SQL (or HQL) queries for entity - loading:</para> - - <programlisting><![CDATA[<sql-query name="person"> - <return alias="pers" class="Person" lock-mode="upgrade"/> - SELECT NAME AS {pers.name}, ID AS {pers.id} - FROM PERSON - WHERE ID=? - FOR UPDATE -</sql-query>]]></programlisting> - - <para>This is just a named query declaration, as discussed earlier. You - may reference this named query in a class mapping:</para> - - <programlisting><![CDATA[<class name="Person"> - <id name="id"> - <generator class="increment"/> - </id> - <property name="name" not-null="true"/> - <loader query-ref="person"/> -</class>]]></programlisting> - - <para>This even works with stored procedures.</para> - - <para>You may even define a query for collection loading:</para> - - <programlisting><![CDATA[<set name="employments" inverse="true"> - <key/> - <one-to-many class="Employment"/> - <loader query-ref="employments"/> -</set>]]></programlisting> - - <programlisting><![CDATA[<sql-query name="employments"> - <load-collection alias="emp" role="Person.employments"/> - SELECT {emp.*} - FROM EMPLOYMENT emp - WHERE EMPLOYER = :id - ORDER BY STARTDATE ASC, EMPLOYEE ASC -</sql-query>]]></programlisting> - - <para>You could even define an entity loader that loads a collection by - join fetching:</para> - - <programlisting><![CDATA[<sql-query name="person"> - <return alias="pers" class="Person"/> - <return-join alias="emp" property="pers.employments"/> - SELECT NAME AS {pers.*}, {emp.*} - FROM PERSON pers - LEFT OUTER JOIN EMPLOYMENT emp - ON pers.ID = emp.PERSON_ID - WHERE ID=? -</sql-query>]]></programlisting> - </sect1> -</chapter> Deleted: core/trunk/documentation/envers/src/main/docbook/en-US/content/session_api.xml =================================================================== --- core/trunk/documentation/envers/src/main/docbook/en-US/content/session_api.xml 2008-11-04 17:31:01 UTC (rev 15499) +++ core/trunk/documentation/envers/src/main/docbook/en-US/content/session_api.xml 2008-11-04 17:31:43 UTC (rev 15500) @@ -1,1287 +0,0 @@ -<?xml version='1.0' encoding="UTF-8"?> -<!-- - ~ Hibernate, Relational Persistence for Idiomatic Java - ~ - ~ Copyright (c) 2008, Red Hat Middleware LLC or third-party contributors as - ~ indicated by the @author tags or express copyright attribution - ~ statements applied by the authors. All third-party contributions are - ~ distributed under license by Red Hat Middleware LLC. - ~ - ~ This copyrighted material is made available to anyone wishing to use, modify, - ~ copy, or redistribute it subject to the terms and conditions of the GNU - ~ Lesser General Public License, as published by the Free Software Foundation. - ~ - ~ This program is distributed in the hope that it will be useful, - ~ but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY - ~ or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License - ~ for more details. - ~ - ~ You should have received a copy of the GNU Lesser General Public License - ~ along with this distribution; if not, write to: - ~ Free Software Foundation, Inc. - ~ 51 Franklin Street, Fifth Floor - ~ Boston, MA 02110-1301 USA - --> - -<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd"> - -<chapter id="objectstate"> - <title>Working with objects</title> - - <para> - Hibernate is a full object/relational mapping solution that not only shields - the developer from the details of the underlying database management - system, but also offers <emphasis>state management</emphasis> of objects. This is, - contrary to the management of SQL <literal>statements</literal> in common JDBC/SQL - persistence layers, a very natural object-oriented view of persistence in Java - applications. - </para> - - <para> - In other words, Hibernate application developers should always think about the - <emphasis>state</emphasis> of their objects, and not necessarily about the - execution of SQL statements. This part is taken care of by Hibernate and is only - relevant for the application developer when tuning the performance of the system. - </para> - - <sect1 id="objectstate-overview"> - <title>Hibernate object states</title> - - <para> - Hibernate defines and supports the following object states: - </para> - - <itemizedlist> - <listitem> - <para> - <emphasis>Transient</emphasis> - an object is transient if it has just - been instantiated using the <literal>new</literal> operator, and it - is not associated with a Hibernate <literal>Session</literal>. It has no - persistent representation in the database and no identifier value has been - assigned. Transient instances will be destroyed by the garbage collector if - the application doesn't hold a reference anymore. Use the Hibernate - <literal>Session</literal> to make an object persistent (and let Hibernate - take care of the SQL statements that need to be executed for this transition). - </para> - </listitem> - <listitem> - <para> - <emphasis>Persistent</emphasis> - a persistent instance has a representation - in the database and an identifier value. It might just have been saved or loaded, - however, it is by definition in the scope of a <literal>Session</literal>. - Hibernate will detect any changes made to an object in persistent state and - synchronize the state with the database when the unit of work completes. - Developers don't execute manual <literal>UPDATE</literal> statements, or - <literal>DELETE</literal> statements when an object should be made transient. - </para> - </listitem> - <listitem> - <para> - <emphasis>Detached</emphasis> - a detached instance is an object that has been - persistent, but its <literal>Session</literal> has been closed. The reference - to the object is still valid, of course, and the detached instance might even - be modified in this state. A detached instance can be reattached to a new - <literal>Session</literal> at a later point in time, making it (and all the - modifications) persistent again. This feature enables a programming model for - long running units of work that require user think-time. We call them - <emphasis>application transactions</emphasis>, i.e. a unit of work from the - point of view of the user. - </para> - </listitem> - </itemizedlist> - - <para> - We'll now discuss the states and state transitions (and the Hibernate methods that - trigger a transition) in more detail. - </para> - - </sect1> - - <sect1 id="objectstate-makingpersistent" revision="1"> - <title>Making objects persistent</title> - - <para> - Newly instantiated instances of a a persistent class are considered - <emphasis>transient</emphasis> by Hibernate. We can make a transient - instance <emphasis>persistent</emphasis> by associating it with a - session: - </para> - - <programlisting><![CDATA[DomesticCat fritz = new DomesticCat(); -fritz.setColor(Color.GINGER); -fritz.setSex('M'); -fritz.setName("Fritz"); -Long generatedId = (Long) sess.save(fritz);]]></programlisting> - - <para> - If <literal>Cat</literal> has a generated identifier, the identifier is - generated and assigned to the <literal>cat</literal> when <literal>save()</literal> - is called. If <literal>Cat</literal> has an <literal>assigned</literal> - identifier, or a composite key, the identifier should be assigned to - the <literal>cat</literal> instance before calling <literal>save()</literal>. - You may also use <literal>persist()</literal> instead of <literal>save()</literal>, - with the semantics defined in the EJB3 early draft. - </para> - - <itemizedlist spacing="compact"> - <listitem> - <para> - <literal>persist()</literal> makes a transient instance persistent. - However, it doesn't guarantee that the identifier value will be assigned to - the persistent instance immediately, the assignment might happen at flush time. - <literal>persist()</literal> also guarantees that it will not execute an - <literal>INSERT</literal> statement if it is called outside of transaction - boundaries. This is useful in long-running conversations with an extended - Session/persistence context. - </para> - </listitem> - <listitem> - <para> - <literal>save()</literal> does guarantee to return an identifier. If an INSERT - has to be executed to get the identifier ( e.g. "identity" generator, not - "sequence"), this INSERT happens immediately, no matter if you are inside or - outside of a transaction. This is problematic in a long-running conversation - with an extended Session/persistence context. - </para> - </listitem> - </itemizedlist> - - <para> - Alternatively, you may assign the identifier using an overloaded version - of <literal>save()</literal>. - </para> - -<programlisting><![CDATA[DomesticCat pk = new DomesticCat(); -pk.setColor(Color.TABBY); -pk.setSex('F'); -pk.setName("PK"); -pk.setKittens( new HashSet() ); -pk.addKitten(fritz); -sess.save( pk, new Long(1234) );]]></programlisting> - - <para> - If the object you make persistent has associated objects (e.g. the - <literal>kittens</literal> collection in the previous example), - these objects may be made persistent in any order you like unless you - have a <literal>NOT NULL</literal> constraint upon a foreign key column. - There is never a risk of violating foreign key constraints. However, you - might violate a <literal>NOT NULL</literal> constraint if you - <literal>save()</literal> the objects in the wrong order. - </para> - - <para> - Usually you don't bother with this detail, as you'll very likely use Hibernate's - <emphasis>transitive persistence</emphasis> feature to save the associated - objects automatically. Then, even <literal>NOT NULL</literal> - constraint violations don't occur - Hibernate will take care of everything. - Transitive persistence is discussed later in this chapter. - </para> - - </sect1> - - <sect1 id="objectstate-loading"> - <title>Loading an object</title> - - <para> - The <literal>load()</literal> methods of <literal>Session</literal> gives you - a way to retrieve a persistent instance if you already know its identifier. - <literal>load()</literal> takes a class object and will load the state into - a newly instantiated instance of that class, in persistent state. - </para> - - <programlisting><![CDATA[Cat fritz = (Cat) sess.load(Cat.class, generatedId);]]></programlisting> - -<programlisting><![CDATA[// you need to wrap primitive identifiers -long id = 1234; -DomesticCat pk = (DomesticCat) sess.load( DomesticCat.class, new Long(id) );]]></programlisting> - - <para> - Alternatively, you can load state into a given instance: - </para> - -<programlisting><![CDATA[Cat cat = new DomesticCat(); -// load pk's state into cat -sess.load( cat, new Long(pkId) ); -Set kittens = cat.getKittens();]]></programlisting> - - <para> - Note that <literal>load()</literal> will throw an unrecoverable exception if - there is no matching database row. If the class is mapped with a proxy, - <literal>load()</literal> just returns an uninitialized proxy and does not - actually hit the database until you invoke a method of the proxy. This - behaviour is very useful if you wish to create an association to an object - without actually loading it from the database. It also allows multiple - instances to be loaded as a batch if <literal>batch-size</literal> is - defined for the class mapping. - </para> - - <para> - If you are not certain that a matching row exists, you should use the - <literal>get()</literal> method, which hits the database immediately and - returns null if there is no matching row. - </para> - - <programlisting><![CDATA[Cat cat = (Cat) sess.get(Cat.class, id); -if (cat==null) { - cat = new Cat(); - sess.save(cat, id); -} -return cat;]]></programlisting> - - <para> - You may even load an object using an SQL <literal>SELECT ... FOR UPDATE</literal>, - using a <literal>LockMode</literal>. See the API documentation for more information. - </para> - - <programlisting><![CDATA[Cat cat = (Cat) sess.get(Cat.class, id, LockMode.UPGRADE);]]></programlisting> - - <para> - Note that any associated instances or contained collections are - <emphasis>not</emphasis> selected <literal>FOR UPDATE</literal>, unless you decide - to specify <literal>lock</literal> or <literal>all</literal> as a - cascade style for the association. - </para> - - <para> - It is possible to re-load an object and all its collections at any time, using the - <literal>refresh()</literal> method. This is useful when database triggers are used to - initialize some of the properties of the object. - </para> - - <programlisting><![CDATA[sess.save(cat); -sess.flush(); //force the SQL INSERT -sess.refresh(cat); //re-read the state (after the trigger executes)]]></programlisting> - - <para> - An important question usually appears at this point: How much does Hibernate load - from the database and how many SQL <literal>SELECT</literal>s will it use? This - depends on the <emphasis>fetching strategy</emphasis> and is explained in - <xref linkend="performance-fetching"/>. - </para> - - </sect1> - - <sect1 id="objectstate-querying" revision="1"> - <title>Querying</title> - - <para> - If you don't know the identifiers of the objects you are looking for, - you need a query. Hibernate supports an easy-to-use but powerful object - oriented query language (HQL). For programmatic query creation, Hibernate - supports a sophisticated Criteria and Example query feature (QBC and QBE). - You may also express your query in the native SQL of your database, with - optional support from Hibernate for result set conversion into objects. - </para> - - <sect2 id="objectstate-querying-executing" revision="1"> - <title>Executing queries</title> - - <para> - HQL and native SQL queries are represented with an instance of <literal>org.hibernate.Query</literal>. - This interface offers methods for parameter binding, result set handling, and for the execution - of the actual query. You always obtain a <literal>Query</literal> using the current - <literal>Session</literal>: - </para> - - <programlisting><![CDATA[List cats = session.createQuery( - "from Cat as cat where cat.birthdate < ?") - .setDate(0, date) - .list(); - -List mothers = session.createQuery( - "select mother from Cat as cat join cat.mother as mother where cat.name = ?") - .setString(0, name) - .list(); - -List kittens = session.createQuery( - "from Cat as cat where cat.mother = ?") - .setEntity(0, pk) - .list(); - -Cat mother = (Cat) session.createQuery( - "select cat.mother from Cat as cat where cat = ?") - .setEntity(0, izi) - .uniqueResult();]] - -Query mothersWithKittens = (Cat) session.createQuery( - "select mother from Cat as mother left join fetch mother.kittens"); -Set uniqueMothers = new HashSet(mothersWithKittens.list());]]></programlisting> - - <para> - A query is usually executed by invoking <literal>list()</literal>, the - result of the query will be loaded completely into a collection in memory. - Entity instances retrieved by a query are in persistent state. The - <literal>uniqueResult()</literal> method offers a shortcut if you - know your query will only return a single object. Note that queries that - make use of eager fetching of collections usually return duplicates of - the root objects (but with their collections initialized). You can filter - these duplicates simply through a <literal>Set</literal>. - </para> - - <sect3 id="objectstate-querying-executing-iterate"> - <title>Iterating results</title> - - <para> - Occasionally, you might be able to achieve better performance by - executing the query using the <literal>iterate()</literal> method. - This will only usually be the case if you expect that the actual - entity instances returned by the query will already be in the session - or second-level cache. If they are not already cached, - <literal>iterate()</literal> will be slower than <literal>list()</literal> - and might require many database hits for a simple query, usually - <emphasis>1</emphasis> for the initial select which only returns identifiers, - and <emphasis>n</emphasis> additional selects to initialize the actual instances. - </para> - - <programlisting><![CDATA[// fetch ids -Iterator iter = sess.createQuery("from eg.Qux q order by q.likeliness").iterate(); -while ( iter.hasNext() ) { - Qux qux = (Qux) iter.next(); // fetch the object - // something we couldnt express in the query - if ( qux.calculateComplicatedAlgorithm() ) { - // delete the current instance - iter.remove(); - // dont need to process the rest - break; - } -}]]></programlisting> - </sect3> - - <sect3 id="objectstate-querying-executing-tuples"> - <title>Queries that return tuples</title> - - <para> - Hibernate queries sometimes return tuples of objects, in which case each tuple - is returned as an array: - </para> - - <programlisting><![CDATA[Iterator kittensAndMothers = sess.createQuery( - "select kitten, mother from Cat kitten join kitten.mother mother") - .list() - .iterator(); - -while ( kittensAndMothers.hasNext() ) { - Object[] tuple = (Object[]) kittensAndMothers.next(); - Cat kitten = (Cat) tuple[0]; - Cat mother = (Cat) tuple[1]; - .... -}]]></programlisting> - - </sect3> - - <sect3 id="objectstate-querying-executing-scalar" revision="1"> - <title>Scalar results</title> - - <para> - Queries may specify a property of a class in the <literal>select</literal> clause. - They may even call SQL aggregate functions. Properties or aggregates are considered - "scalar" results (and not entities in persistent state). - </para> - - <programlisting><![CDATA[Iterator results = sess.createQuery( - "select cat.color, min(cat.birthdate), count(cat) from Cat cat " + - "group by cat.color") - .list() - .iterator(); - -while ( results.hasNext() ) { - Object[] row = (Object[]) results.next(); - Color type = (Color) row[0]; - Date oldest = (Date) row[1]; - Integer count = (Integer) row[2]; - ..... -}]]></programlisting> - - </sect3> - - <sect3 id="objectstate-querying-executing-parameters"> - <title>Bind parameters</title> - - <para> - Methods on <literal>Query</literal> are provided for binding values to - named parameters or JDBC-style <literal>?</literal> parameters. - <emphasis>Contrary to JDBC, Hibernate numbers parameters from zero.</emphasis> - Named parameters are identifiers of the form <literal>:name</literal> in - the query string. The advantages of named parameters are: - </para> - - <itemizedlist spacing="compact"> - <listitem> - <para> - named parameters are insensitive to the order they occur in the - query string - </para> - </listitem> - <listitem> - <para> - they may occur multiple times in the same query - </para> - </listitem> - <listitem> - <para> - they are self-documenting - </para> - </listitem> - </itemizedlist> - - <programlisting><![CDATA[//named parameter (preferred) -Query q = sess.createQuery("from DomesticCat cat where cat.name = :name"); -q.setString("name", "Fritz"); -Iterator cats = q.iterate();]]></programlisting> - - <programlisting><![CDATA[//positional parameter -Query q = sess.createQuery("from DomesticCat cat where cat.name = ?"); -q.setString(0, "Izi"); -Iterator cats = q.iterate();]]></programlisting> - - <programlisting><![CDATA[//named parameter list -List names = new ArrayList(); -names.add("Izi"); -names.add("Fritz"); -Query q = sess.createQuery("from DomesticCat cat where cat.name in (:namesList)"); -q.setParameterList("namesList", names); -List cats = q.list();]]></programlisting> - - </sect3> - - <sect3 id="objectstate-querying-executing-pagination"> - <title>Pagination</title> - - <para> - If you need to specify bounds upon your result set (the maximum number of rows - you want to retrieve and / or the first row you want to retrieve) you should - use methods of the <literal>Query</literal> interface: - </para> - - <programlisting><![CDATA[Query q = sess.createQuery("from DomesticCat cat"); -q.setFirstResult(20); -q.setMaxResults(10); -List cats = q.list();]]></programlisting> - - <para> - Hibernate knows how to translate this limit query into the native - SQL of your DBMS. - </para> - - </sect3> - - <sect3 id="objectstate-querying-executing-scrolling"> - <title>Scrollable iteration</title> - - <para> - If your JDBC driver supports scrollable <literal>ResultSet</literal>s, the - <literal>Query</literal> interface may be used to obtain a - <literal>ScrollableResults</literal> object, which allows flexible - navigation of the query results. - </para> - - <programlisting><![CDATA[Query q = sess.createQuery("select cat.name, cat from DomesticCat cat " + - "order by cat.name"); -ScrollableResults cats = q.scroll(); -if ( cats.first() ) { - - // find the first name on each page of an alphabetical list of cats by name - firstNamesOfPages = new ArrayList(); - do { - String name = cats.getString(0); - firstNamesOfPages.add(name); - } - while ( cats.scroll(PAGE_SIZE) ); - - // Now get the first page of cats - pageOfCats = new ArrayList(); - cats.beforeFirst(); - int i=0; - while( ( PAGE_SIZE > i++ ) && cats.next() ) pageOfCats.add( cats.get(1) ); - -} -cats.close()]]></programlisting> - - <para> - Note that an open database connection (and cursor) is required for this - functionality, use <literal>setMaxResult()</literal>/<literal>setFirstResult()</literal> - if you need offline pagination functionality. - </para> - - </sect3> - - <sect3 id="objectstate-querying-executing-named" revision="1"> - <title>Externalizing named queries</title> - - <para> - You may also define named queries in the mapping document. (Remember to use a - <literal>CDATA</literal> section if your query contains characters that could - be interpreted as markup.) - </para> - - <programlisting><![CDATA[<query name="ByNameAndMaximumWeight"><![CDATA[ - from eg.DomesticCat as cat - where cat.name = ? - and cat.weight > ? -] ]></query>]]></programlisting> - - <para> - Parameter binding and executing is done programatically: - </para> - - <programlisting><![CDATA[Query q = sess.getNamedQuery("ByNameAndMaximumWeight"); -q.setString(0, name); -q.setInt(1, minWeight); -List cats = q.list();]]></programlisting> - - <para> - Note that the actual program code is independent of the query language that - is used, you may also define native SQL queries in metadata, or migrate - existing queries to Hibernate by placing them in mapping files. - </para> - - <para> - Also note that a query declaration inside a <literal>&lt;hibernate-mapping&gt;</literal> - element requires a global unique name for the query, while a query declaration inside a - <literal>&lt;class&gt;</literal> element is made unique automatically by prepending the - fully qualified name of the class, for example - <literal>eg.Cat.ByNameAndMaximumWeight</literal>. - </para> - - </sect3> - - </sect2> - - <sect2 id="objectstate-filtering" revision="1"> - <title>Filtering collections</title> - <para> - A collection <emphasis>filter</emphasis> is a special type of query that may be applied to - a persistent collection or array. The query string may refer to <literal>this</literal>, - meaning the current collection element. - </para> - - <programlisting><![CDATA[Collection blackKittens = session.createFilter( - pk.getKittens(), - "where this.color = ?") - .setParameter( Color.BLACK, Hibernate.custom(ColorUserType.class) ) - .list() -);]]></programlisting> - - <para> - The returned collection is considered a bag, and it's a copy of the given - collection. The original collection is not modified (this is contrary to - the implication of the name "filter", but consistent with expected behavior). - </para> - - <para> - Observe that filters do not require a <literal>from</literal> clause (though they may have - one if required). Filters are not limited to returning the collection elements themselves. - </para> - - <programlisting><![CDATA[Collection blackKittenMates = session.createFilter( - pk.getKittens(), - "select this.mate where this.color = eg.Color.BLACK.intValue") - .list();]]></programlisting> - - <para> - Even an empty filter query is useful, e.g. to load a subset of elements in a - huge collection: - </para> - - <programlisting><![CDATA[Collection tenKittens = session.createFilter( - mother.getKittens(), "") - .setFirstResult(0).setMaxResults(10) - .list();]]></programlisting> - - </sect2> - - <sect2 id="objecstate-querying-criteria" revision="1"> - <title>Criteria queries</title> - - <para> - HQL is extremely powerful but some developers prefer to build queries dynamically, - using an object-oriented API, rather than building query strings. Hibernate provides - an intuitive <literal>Criteria</literal> query API for these cases: - </para> - - <programlisting><![CDATA[Criteria crit = session.createCriteria(Cat.class); -crit.add( Restrictions.eq( "color", eg.Color.BLACK ) ); -crit.setMaxResults(10); -List cats = crit.list();]]></programlisting> - - <para> - The <literal>Criteria</literal> and the associated <literal>Example</literal> - API are discussed in more detail in <xref linkend="querycriteria"/>. - </para> - - </sect2> - - <sect2 id="objectstate-querying-nativesql" revision="2"> - <title>Queries in native SQL</title> - - <para> - You may express a query in SQL, using <literal>createSQLQuery()</literal> and - let Hibernate take care of the mapping from result sets to objects. Note - that you may at any time call <literal>session.connection()</literal> and - use the JDBC <literal>Connection</literal> directly. If you chose to use the - Hibernate API, you must enclose SQL aliases in braces: - </para> - - <programlisting><![CDATA[List cats = session.createSQLQuery("SELECT {cat.*} FROM CAT {cat} WHERE ROWNUM<10") - .addEntity("cat", Cat.class) -.list();]]></programlisting> - - <programlisting><![CDATA[List cats = session.createSQLQuery( - "SELECT {cat}.ID AS {cat.id}, {cat}.SEX AS {cat.sex}, " + - "{cat}.MATE AS {cat.mate}, {cat}.SUBCLASS AS {cat.class}, ... " + - "FROM CAT {cat} WHERE ROWNUM<10") - .addEntity("cat", Cat.class) -.list()]]></programlisting> - - <para> - SQL queries may contain named and positional parameters, just like Hibernate queries. - More information about native SQL queries in Hibernate can be found in - <xref linkend="querysql"/>. - </para> - - </sect2> - - </sect1> - - <sect1 id="objectstate-modifying" revision="1"> - <title>Modifying persistent objects</title> - - <para> - <emphasis>Transactional persistent instances</emphasis> (ie. objects loaded, saved, created or - queried by the <literal>Session</literal>) may be manipulated by the application - and any changes to persistent state will be persisted when the <literal>Session</literal> - is <emphasis>flushed</emphasis> (discussed later in this chapter). There is no need - to call a particular method (like <literal>update()</literal>, which has a different - purpose) to make your modifications persistent. So the most straightforward way to update - the state of an object is to <literal>load()</literal> it, - and then manipulate it directly, while the <literal>Session</literal> is open: - </para> - - <programlisting><![CDATA[DomesticCat cat = (DomesticCat) sess.load( Cat.class, new Long(69) ); -cat.setName("PK"); -sess.flush(); // changes to cat are automatically detected and persisted]]></programlisting> - - <para> - Sometimes this programming model is inefficient since it would require both an SQL - <literal>SELECT</literal> (to load an object) and an SQL <literal>UPDATE</literal> - (to persist its updated state) in the same session. Therefore Hibernate offers an - alternate approach, using detached instances. - </para> - - <para> - <emphasis>Note that Hibernate does not offer its own API for direct execution of - <literal>UPDATE</literal> or <literal>DELETE</literal> statements. Hibernate is a - <emphasis>state management</emphasis> service, you don't have to think in - <emphasis>statements</emphasis> to use it. JDBC is a perfect API for executing - SQL statements, you can get a JDBC <literal>Connection</literal> at any time - by calling <literal>session.connection()</literal>. Furthermore, the notion - of mass operations conflicts with object/relational mapping for online - transaction processing-oriented applications. Future versions of Hibernate - may however provide special mass operation functions. See <xref linkend="batch"/> - for some possible batch operation tricks.</emphasis> - </para> - - </sect1> - - <sect1 id="objectstate-detached" revision="2"> - <title>Modifying detached objects</title> - - <para> - Many applications need to retrieve an object in one transaction, send it to the - UI layer for manipulation, then save the changes in a new transaction. - Applications that use this kind of approach in a high-concurrency environment - usually use versioned data to ensure isolation for the "long" unit of work. - </para> - - <para> - Hibernate supports this model by providing for reattachment of detached instances - using the <literal>Session.update()</literal> or <literal>Session.merge()</literal> - methods: - </para> - - <programlisting><![CDATA[// in the first session -Cat cat = (Cat) firstSession.load(Cat.class, catId); -Cat potentialMate = new Cat(); -firstSession.save(potentialMate); - -// in a higher layer of the application -cat.setMate(potentialMate); - -// later, in a new session -secondSession.update(cat); // update cat -secondSession.update(mate); // update mate]]></programlisting> - - <para> - If the <literal>Cat</literal> with identifier <literal>catId</literal> had already - been loaded by <literal>secondSession</literal> when the application tried to - reattach it, an exception would have been thrown. - </para> - - <para> - Use <literal>update()</literal> if you are sure that the session does - not contain an already persistent instance with the same identifier, and - <literal>merge()</literal> if you want to merge your modifications at any time - without consideration of the state of the session. In other words, <literal>update()</literal> - is usually the first method you would call in a fresh session, ensuring that - reattachment of your detached instances is the first operation that is executed. - </para> - - <para> - The application should individually <literal>update()</literal> detached instances - reachable from the given detached instance if and <emphasis>only</emphasis> if it wants - their state also updated. This can be automated of course, using <emphasis>transitive - persistence</emphasis>, see <xref linkend="objectstate-transitive"/>. - </para> - - <para> - The <literal>lock()</literal> method also allows an application to reassociate - an object with a new session. However, the detached instance has to be unmodified! - </para> - - <programlisting><![CDATA[//just reassociate: -sess.lock(fritz, LockMode.NONE); -//do a version check, then reassociate: -sess.lock(izi, LockMode.READ); -//do a version check, using SELECT ... FOR UPDATE, then reassociate: -sess.lock(pk, LockMode.UPGRADE);]]></programlisting> - - <para> - Note that <literal>lock()</literal> can be used with various - <literal>LockMode</literal>s, see the API documentation and the - chapter on transaction handling for more information. Reattachment is not - the only usecase for <literal>lock()</literal>. - </para> - - <para> - Other models for long units of work are discussed in <xref linkend="transactions-optimistic"/>. - </para> - - </sect1> - - <sect1 id="objectstate-saveorupdate"> - <title>Automatic state detection</title> - - <para> - Hibernate users have requested a general purpose method that either saves a - transient instance by generating a new identifier or updates/reattaches - the detached instances associated with its current identifier. - The <literal>saveOrUpdate()</literal> method implements this functionality. - </para> - - <programlisting><![CDATA[// in the first session -Cat cat = (Cat) firstSession.load(Cat.class, catID); - -// in a higher tier of the application -Cat mate = new Cat(); -cat.setMate(mate); - -// later, in a new session -secondSession.saveOrUpdate(cat); // update existing state (cat has a non-null id) -secondSession.saveOrUpdate(mate); // save the new instance (mate has a null id)]]></programlisting> - - <para> - The usage and semantics of <literal>saveOrUpdate()</literal> seems to be confusing - for new users. Firstly, so long as you are not trying to use instances from one session - in another new session, you should not need to use <literal>update()</literal>, - <literal>saveOrUpdate()</literal>, or <literal>merge()</literal>. Some whole - applications will never use either of these methods. - </para> - - <para> - Usually <literal>update()</literal> or <literal>saveOrUpdate()</literal> are used in - the following scenario: - </para> - - <itemizedlist spacing="compact"> - <listitem> - <para> - the application loads an object in the first session - </para> - </listitem> - <listitem> - <para> - the object is passed up to the UI tier - </para> - </listitem> - <listitem> - <para> - some modifications are made to the object - </para> - </listitem> - <listitem> - <para> - the object is passed back down to the business logic tier - </para> - </listitem> - <listitem> - <para> - the application persists these modifications by calling - <literal>update()</literal> in a second session - </para> - </listitem> - </itemizedlist> - - <para> - <literal>saveOrUpdate()</literal> does the following: - </para> - - <itemizedlist spacing="compact"> - <listitem> - <para> - if the object is already persistent in this session, do nothing - </para> - </listitem> - <listitem> - <para> - if another object associated with the session has the same identifier, - throw an exception - </para> - </listitem> - <listitem> - <para> - if the object has no identifier property, <literal>save()</literal> it - </para> - </listitem> - <listitem> - <para> - if the object's identifier has the value assigned to a newly instantiated - object, <literal>save()</literal> it - </para> - </listitem> - <listitem> - <para> - if the object is versioned (by a <literal>&lt;version&gt;</literal> or - <literal>&lt;timestamp&gt;</literal>), and the version property value - is the same value assigned to a newly instantiated object, - <literal>save()</literal> it - </para> - </listitem> - <listitem> - <para> - otherwise <literal>update()</literal> the object - </para> - </listitem> - </itemizedlist> - - <para> - and <literal>merge()</literal> is very different: - </para> - - <itemizedlist spacing="compact"> - <listitem> - <para> - if there is a persistent instance with the same identifier currently - associated with the session, copy the state of the given object onto - the persistent instance - </para> - </listitem> - <listitem> - <para> - if there is no persistent instance currently associated with the session, - try to load it from the database, or create a new persistent instance - </para> - </listitem> - <listitem> - <para> - the persistent instance is returned - </para> - </listitem> - <listitem> - <para> - the given instance does not become associated with the session, it - remains detached - </para> - </listitem> - </itemizedlist> - - </sect1> - - <sect1 id="objectstate-deleting" revision="1"> - <title>Deleting persistent objects</title> - - <para> - <literal>Session.delete()</literal> will remove an object's state from the database. - Of course, your application might still hold a reference to a deleted object. - It's best to think of <literal>delete()</literal> as making a persistent instance - transient. - </para> - - <programlisting><![CDATA[sess.delete(cat);]]></programlisting> - - <para> - You may delete objects in any order you like, without risk of foreign key - constraint violations. It is still possible to violate a <literal>NOT - NULL</literal> constraint on a foreign key column by deleting objects in - the wrong order, e.g. if you delete the parent, but forget to delete the - children. - </para> - - </sect1> - - <sect1 id="objectstate-replicating" revision="1"> - <title>Replicating object between two different datastores</title> - - <para> - It is occasionally useful to be able to take a graph of persistent instances - and make them persistent in a different datastore, without regenerating identifier - values. - </para> - - <programlisting><![CDATA[//retrieve a cat from one database -Session session1 = factory1.openSession(); -Transaction tx1 = session1.beginTransaction(); -Cat cat = session1.get(Cat.class, catId); -tx1.commit(); -session1.close(); - -//reconcile with a second database -Session session2 = factory2.openSession(); -Transaction tx2 = session2.beginTransaction(); -session2.replicate(cat, ReplicationMode.LATEST_VERSION); -tx2.commit(); -session2.close();]]></programlisting> - - <para> - The <literal>ReplicationMode</literal> determines how <literal>replicate()</literal> - will deal with conflicts with existing rows in the database. - </para> - - <itemizedlist spacing="compact"> - <listitem> - <para> - <literal>ReplicationMode.IGNORE</literal> - ignore the object when there is - an existing database row with the same identifier - </para> - </listitem> - <listitem> - <para> - <literal>ReplicationMode.OVERWRITE</literal> - overwrite any existing database - row with the same identifier - </para> - </listitem> - <listitem> - <para> - <literal>ReplicationMode.EXCEPTION</literal> - throw an exception if there is - an existing database row with the same identifier - </para> - </listitem> - <listitem> - <para> - <literal>ReplicationMode.LATEST_VERSION</literal> - overwrite the row if its - version number is earlier than the version number of the object, or ignore - the object otherwise - </para> - </listitem> - </itemizedlist> - - <para> - Usecases for this feature include reconciling data entered into different database - instances, upgrading system configuration information during product upgrades, - rolling back changes made during non-ACID transactions and more. - </para> - - </sect1> - - <sect1 id="objectstate-flushing"> - <title>Flushing the Session</title> - - <para> - From time to time the <literal>Session</literal> will execute the SQL statements - needed to synchronize the JDBC connection's state with the state of objects held in - memory. This process, <emphasis>flush</emphasis>, occurs by default at the following - points - </para> - - <itemizedlist spacing="compact"> - <listitem> - <para> - before some query executions - </para> - </listitem> - <listitem> - <para> - from <literal>org.hibernate.Transaction.commit()</literal> - </para> - </listitem> - <listitem> - <para> - from <literal>Session.flush()</literal> - </para> - </listitem> - </itemizedlist> - - <para> - The SQL statements are issued in the following order - </para> - - <orderedlist spacing="compact"> - <listitem> - <para> - all entity insertions, in the same order the corresponding objects - were saved using <literal>Session.save()</literal> - </para> - </listitem> - <listitem> - <para> - all entity updates - </para> - </listitem> - <listitem> - <para> - all collection deletions - </para> - </listitem> - <listitem> - <para> - all collection element deletions, updates and insertions - </para> - </listitem> - <listitem> - <para> - all collection insertions - </para> - </listitem> - <listitem> - <para> - all entity deletions, in the same order the corresponding objects - were deleted using <literal>Session.delete()</literal> - </para> - </listitem> - </orderedlist> - - <para> - (An exception is that objects using <literal>native</literal> ID generation are - inserted when they are saved.) - </para> - - <para> - Except when you explicity <literal>flush()</literal>, there are absolutely no - guarantees about <emphasis>when</emphasis> the <literal>Session</literal> executes - the JDBC calls, only the <emphasis>order</emphasis> in which they are executed. - However, Hibernate does guarantee that the <literal>Query.list(..)</literal> - will never return stale data; nor will they return the wrong data. - </para> - - <para> - It is possible to change the default behavior so that flush occurs less frequently. - The <literal>FlushMode</literal> class defines three different modes: only flush - at commit time (and only when the Hibernate <literal>Transaction</literal> API - is used), flush automatically using the explained routine, or never flush unless - <literal>flush()</literal> is called explicitly. The last mode is useful for long running - units of work, where a <literal>Session</literal> is kept open and disconnected for - a long time (see <xref linkend="transactions-optimistic-longsession"/>). - </para> - - <programlisting><![CDATA[sess = sf.openSession(); -Transaction tx = sess.beginTransaction(); -sess.setFlushMode(FlushMode.COMMIT); // allow queries to return stale state - -Cat izi = (Cat) sess.load(Cat.class, id); -izi.setName(iznizi); - -// might return stale data -sess.find("from Cat as cat left outer join cat.kittens kitten"); - -// change to izi is not flushed! -... -tx.commit(); // flush occurs -sess.close();]]></programlisting> - - <para> - During flush, an exception might occur (e.g. if a DML operation violates a constraint). - Since handling exceptions involves some understanding of Hibernate's transactional - behavior, we discuss it in <xref linkend="transactions"/>. - </para> - - </sect1> - - <sect1 id="objectstate-transitive" revision="1"> - <title>Transitive persistence</title> - - <para> - It is quite cumbersome to save, delete, or reattach individual objects, - especially if you deal with a graph of associated objects. A common case is - a parent/child relationship. Consider the following example: - </para> - - <para> - If the children in a parent/child relationship would be value typed (e.g. a collection - of addresses or strings), their life cycle would depend on the parent and no - further action would be required for convenient "cascading" of state changes. - When the parent is saved, the value-typed child objects are saved as - well, when the parent is deleted, the children will be deleted, etc. This - even works for operations such as the removal of a child from the collection; - Hibernate will detect this and, since value-typed objects can't have shared - references, delete the child from the database. - </para> - - <para> - Now consider the same scenario with parent and child objects being entities, - not value-types (e.g. categories and items, or parent and child cats). Entities - have their own life cycle, support shared references (so removing an entity from - the collection does not mean it can be deleted), and there is by default no - cascading of state from one entity to any other associated entities. Hibernate - does not implement <emphasis>persistence by reachability</emphasis> by default. - </para> - - <para> - For each basic operation of the Hibernate session - including <literal>persist(), merge(), - saveOrUpdate(), delete(), lock(), refresh(), evict(), replicate()</literal> - there is a - corresponding cascade style. Respectively, the cascade styles are named <literal>create, - merge, save-update, delete, lock, refresh, evict, replicate</literal>. If you want an - operation to be cascaded along an association, you must indicate that in the mapping - document. For example: - </para> - - <programlisting><![CDATA[<one-to-one name="person" cascade="persist"/>]]></programlisting> - - <para> - Cascade styles my be combined: - </para> - - <programlisting><![CDATA[<one-to-one name="person" cascade="persist,delete,lock"/>]]></programlisting> - - <para> - You may even use <literal>cascade="all"</literal> to specify that <emphasis>all</emphasis> - operations should be cascaded along the association. The default <literal>cascade="none"</literal> - specifies that no operations are to be cascaded. - </para> - - <para> - A special cascade style, <literal>delete-orphan</literal>, applies only to one-to-many - associations, and indicates that the <literal>delete()</literal> operation should - be applied to any child object that is removed from the association. - </para> - - - <para> - Recommendations: - </para> - - <itemizedlist spacing="compact"> - <listitem> - <para> - It doesn't usually make sense to enable cascade on a <literal>&lt;many-to-one&gt;</literal> - or <literal>&lt;many-to-many&gt;</literal> association. Cascade is often useful for - <literal>&lt;one-to-one&gt;</literal> and <literal>&lt;one-to-many&gt;</literal> - associations. - </para> - </listitem> - <listitem> - <para> - If the child object's lifespan is bounded by the lifespan of the parent - object, make it a <emphasis>life cycle object</emphasis> by specifying - <literal>cascade="all,delete-orphan"</literal>. - </para> - </listitem> - <listitem> - <para> - Otherwise, you might not need cascade at all. But if you think that you will often be - working with the parent and children together in the same transaction, and you want to save - yourself some typing, consider using <literal>cascade="persist,merge,save-update"</literal>. - </para> - </listitem> - </itemizedlist> - - <para> - Mapping an association (either a single valued association, or a collection) with - <literal>cascade="all"</literal> marks the association as a - <emphasis>parent/child</emphasis> style relationship where save/update/delete of the - parent results in save/update/delete of the child or children. - </para> - <para> - Futhermore, a mere reference to a child from a persistent parent will result in - save/update of the child. This metaphor is incomplete, however. A child which becomes - unreferenced by its parent is <emphasis>not</emphasis> automatically deleted, except - in the case of a <literal>&lt;one-to-many&gt;</literal> association mapped with - <literal>cascade="delete-orphan"</literal>. The precise semantics of cascading - operations for a parent/child relationship are as follows: - </para> - - <itemizedlist spacing="compact"> - <listitem> - <para> - If a parent is passed to <literal>persist()</literal>, all children are passed to - <literal>persist()</literal> - </para> - </listitem> - <listitem> - <para> - If a parent is passed to <literal>merge()</literal>, all children are passed to - <literal>merge()</literal> - </para> - </listitem> - <listitem> - <para> - If a parent is passed to <literal>save()</literal>, <literal>update()</literal> or - <literal>saveOrUpdate()</literal>, all children are passed to <literal>saveOrUpdate()</literal> - </para> - </listitem> - <listitem> - <para> - If a transient or detached child becomes referenced by a persistent parent, - it is passed to <literal>saveOrUpdate()</literal> - </para> - </listitem> - <listitem> - <para> - If a parent is deleted, all children are passed to <literal>delete()</literal> - </para> - </listitem> - <listitem> - <para> - If a child is dereferenced by a persistent parent, <emphasis>nothing - special happens</emphasis> - the application should explicitly delete - the child if necessary - unless <literal>cascade="delete-orphan"</literal>, - in which case the "orphaned" child is deleted. - </para> - </listitem> - </itemizedlist> - - <para> - Finally, note that cascading of operations can be applied to an object graph at - <emphasis>call time</emphasis> or at <emphasis>flush time</emphasis>. All operations, - if enabled, are cascaded to associated entities reachable when the operation is - executed. However, <literal>save-upate</literal> and <literal>delete-orphan</literal> - are transitive for all associated entities reachable during flush of the - <literal>Session</literal>. - </para> - - </sect1> - - <sect1 id="objectstate-metadata"> - <title>Using metadata</title> - - <para> - Hibernate requires a very rich meta-level model of all entity and value types. From time - to time, this model is very useful to the application itself. For example, the application - might use Hibernate's metadata to implement a "smart" deep-copy algorithm that understands - which objects should be copied (eg. mutable value types) and which should not (eg. - immutable value types and, possibly, associated entities). - </para> - <para> - Hibernate exposes metadata via the <literal>ClassMetadata</literal> and - <literal>CollectionMetadata</literal> interfaces and the <literal>Type</literal> - hierarchy. Instances of the metadata interfaces may be obtained from the - <literal>SessionFactory</literal>. - </para> - - <programlisting><![CDATA[Cat fritz = ......; -ClassMetadata catMeta = sessionfactory.getClassMetadata(Cat.class); - -Object[] propertyValues = catMeta.getPropertyValues(fritz); -String[] propertyNames = catMeta.getPropertyNames(); -Type[] propertyTypes = catMeta.getPropertyTypes(); - -// get a Map of all properties which are not collections or associations -Map namedValues = new HashMap(); -for ( int i=0; i<propertyNames.length; i++ ) { - if ( !propertyTypes[i].isEntityType() && !propertyTypes[i].isCollectionType() ) { - namedValues.put( propertyNames[i], propertyValues[i] ); - } -}]]></programlisting> - - </sect1> - -</chapter> - Deleted: core/trunk/documentation/envers/src/main/docbook/en-US/content/toolset_guide.xml =================================================================== --- core/trunk/documentation/envers/src/main/docbook/en-US/content/toolset_guide.xml 2008-11-04 17:31:01 UTC (rev 15499) +++ core/trunk/documentation/envers/src/main/docbook/en-US/content/toolset_guide.xml 2008-11-04 17:31:43 UTC (rev 15500) @@ -1,631 +0,0 @@ -<?xml version='1.0' encoding="UTF-8"?> -<!-- - ~ Hibernate, Relational Persistence for Idiomatic Java - ~ - ~ Copyright (c) 2008, Red Hat Middleware LLC or third-party contributors as - ~ indicated by the @author tags or express copyright attribution - ~ statements applied by the authors. All third-party contributions are - ~ distributed under license by Red Hat Middleware LLC. - ~ - ~ This copyrighted material is made available to anyone wishing to use, modify, - ~ copy, or redistribute it subject to the terms and conditions of the GNU - ~ Lesser General Public License, as published by the Free Software Foundation. - ~ - ~ This program is distributed in the hope that it will be useful, - ~ but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY - ~ or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License - ~ for more details. - ~ - ~ You should have received a copy of the GNU Lesser General Public License - ~ along with this distribution; if not, write to: - ~ Free Software Foundation, Inc. - ~ 51 Franklin Street, Fifth Floor - ~ Boston, MA 02110-1301 USA - --> - -<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd"> - -<chapter id="toolsetguide" revision="2"> - <title>Toolset Guide</title> - - <para> - Roundtrip engineering with Hibernate is possible using a set of Eclipse plugins, - commandline tools, as well as Ant tasks. - </para> - - <para> - The <emphasis>Hibernate Tools</emphasis> currently include plugins for the Eclipse - IDE as well as Ant tasks for reverse engineering of existing databases: - </para> - - <itemizedlist> - <listitem><para> - <emphasis>Mapping Editor:</emphasis> An editor for Hibernate XML mapping files, - supporting auto-completion and syntax highlighting. It also supports semantic - auto-completion for class names and property/field names, making it much more versatile than a normal XML editor. - </para></listitem> - <listitem><para> - <emphasis>Console:</emphasis> The console is a new view in Eclipse. In addition to - a tree overview of your console configurations, you also get an interactive view - of your persistent classes and their relationships. The console allows you to - execute HQL queries against your database and browse the result directly in - Eclipse. - </para></listitem> - <listitem><para> - <emphasis>Development Wizards:</emphasis> Several wizards are provided with the - Hibernate Eclipse tools; you can use a wizard to quickly generate Hibernate configuration - (cfg.xml) files, or you may even completely reverse engineer an existing database schema - into POJO source files and Hibernate mapping files. The reverse engineering wizard - supports customizable templates. - </para></listitem> - <listitem><para> - <emphasis>Ant Tasks:</emphasis> - </para></listitem> - - </itemizedlist> - - <para> - Please refer to the <emphasis>Hibernate Tools</emphasis> package and it's documentation - for more information. - </para> - - <para> - However, the Hibernate main package comes bundled with an integrated tool (it can even - be used from "inside" Hibernate on-the-fly): <emphasis>SchemaExport</emphasis> aka - <literal>hbm2ddl</literal>. - </para> - - <sect1 id="toolsetguide-s1" revision="2"> - <title>Automatic schema generation</title> - - <para> - DDL may be generated from your mapping files by a Hibernate utility. The generated - schema includes referential integrity constraints (primary and foreign keys) for - entity and collection tables. Tables and sequences are also created for mapped - identifier generators. - </para> - - <para> - You <emphasis>must</emphasis> specify a SQL <literal>Dialect</literal> via the - <literal>hibernate.dialect</literal> property when using this tool, as DDL - is highly vendor specific. - </para> - - <para> - First, customize your mapping files to improve the generated schema. - </para> - - <sect2 id="toolsetguide-s1-2" revision="3"> - <title>Customizing the schema</title> - - <para> - Many Hibernate mapping elements define optional attributes named <literal>length</literal>, - <literal>precision</literal> and <literal>scale</literal>. You may set the length, precision - and scale of a column with this attribute. - - </para> - - <programlisting><![CDATA[<property name="zip" length="5"/>]]></programlisting> - <programlisting><![CDATA[<property name="balance" precision="12" scale="2"/>]]></programlisting> - - <para> - Some tags also accept a <literal>not-null</literal> attribute (for generating a - <literal>NOT NULL</literal> constraint on table columns) and a <literal>unique</literal> - attribute (for generating <literal>UNIQUE</literal> constraint on table columns). - </para> - - <programlisting><![CDATA[<many-to-one name="bar" column="barId" not-null="true"/>]]></programlisting> - - <programlisting><![CDATA[<element column="serialNumber" type="long" not-null="true" unique="true"/>]]></programlisting> - - <para> - A <literal>unique-key</literal> attribute may be used to group columns in - a single unique key constraint. Currently, the specified value of the - <literal>unique-key</literal> attribute is <emphasis>not</emphasis> used - to name the constraint in the generated DDL, only to group the columns in - the mapping file. - </para> - - <programlisting><![CDATA[<many-to-one name="org" column="orgId" unique-key="OrgEmployeeId"/> -<property name="employeeId" unique-key="OrgEmployee"/>]]></programlisting> - - <para> - An <literal>index</literal> attribute specifies the name of an index that - will be created using the mapped column or columns. Multiple columns may be - grouped into the same index, simply by specifying the same index name. - </para> - - <programlisting><![CDATA[<property name="lastName" index="CustName"/> -<property name="firstName" index="CustName"/>]]></programlisting> - - <para> - A <literal>foreign-key</literal> attribute may be used to override the name - of any generated foreign key constraint. - </para> - - <programlisting><![CDATA[<many-to-one name="bar" column="barId" foreign-key="FKFooBar"/>]]></programlisting> - - <para> - Many mapping elements also accept a child <literal>&lt;column&gt;</literal> element. - This is particularly useful for mapping multi-column types: - </para> - - <programlisting><![CDATA[<property name="name" type="my.customtypes.Name"/> - <column name="last" not-null="true" index="bar_idx" length="30"/> - <column name="first" not-null="true" index="bar_idx" length="20"/> - <column name="initial"/> -</property>]]></programlisting> - - <para> - The <literal>default</literal> attribute lets you specify a default value for - a column (you should assign the same value to the mapped property before - saving a new instance of the mapped class). - </para> - - <programlisting><![CDATA[<property name="credits" type="integer" insert="false"> - <column name="credits" default="10"/> -</property>]]></programlisting> - - <programlisting><![CDATA[<version name="version" type="integer" insert="false"> - <column name="version" default="0"/> -</property>]]></programlisting> - - <para> - The <literal>sql-type</literal> attribute allows the user to override the default - mapping of a Hibernate type to SQL datatype. - </para> - - <programlisting><![CDATA[<property name="balance" type="float"> - <column name="balance" sql-type="decimal(13,3)"/> -</property>]]></programlisting> - - <para> - The <literal>check</literal> attribute allows you to specify a check constraint. - </para> - - <programlisting><![CDATA[<property name="foo" type="integer"> - <column name="foo" check="foo > 10"/> -</property>]]></programlisting> - - <programlisting><![CDATA[<class name="Foo" table="foos" check="bar < 100.0"> - ... - <property name="bar" type="float"/> -</class>]]></programlisting> - - - <table frame="topbot" id="schemattributes-summary" revision="2"> - <title>Summary</title> - <tgroup cols="3"> - <colspec colwidth="1*"/> - <colspec colwidth="1*"/> - <colspec colwidth="2.5*"/> - <thead> - <row> - <entry>Attribute</entry> - <entry>Values</entry> - <entry>Interpretation</entry> - </row> - </thead> - <tbody> - <row> - <entry><literal>length</literal></entry> - <entry>number</entry> - <entry>column length</entry> - </row> - <row> - <entry><literal>precision</literal></entry> - <entry>number</entry> - <entry>column decimal precision</entry> - </row> - <row> - <entry><literal>scale</literal></entry> - <entry>number</entry> - <entry>column decimal scale</entry> - </row> - <row> - <entry><literal>not-null</literal></entry> - <entry><literal>true|false</literal></entry> - <entry>specfies that the column should be non-nullable</entry> - </row> - <row> - <entry><literal>unique</literal></entry> - <entry><literal>true|false</literal></entry> - <entry>specifies that the column should have a unique constraint</entry> - </row> - <row> - <entry><literal>index</literal></entry> - <entry><literal>index_name</literal></entry> - <entry>specifies the name of a (multi-column) index</entry> - </row> - <row> - <entry><literal>unique-key</literal></entry> - <entry><literal>unique_key_name</literal></entry> - <entry>specifies the name of a multi-column unique constraint</entry> - </row> - <row> - <entry><literal>foreign-key</literal></entry> - <entry><literal>foreign_key_name</literal></entry> - <entry> - specifies the name of the foreign key constraint generated - for an association, for a <literal>&lt;one-to-one&gt;</literal>, - <literal>&lt;many-to-one&gt;</literal>, <literal>&lt;key&gt;</literal>, - or <literal>&lt;many-to-many&gt;</literal> mapping element. Note that - <literal>inverse="true"</literal> sides will not be considered - by <literal>SchemaExport</literal>. - </entry> - </row> - <row> - <entry><literal>sql-type</literal></entry> - <entry><literal>SQL column type</literal></entry> - <entry> - overrides the default column type (attribute of - <literal>&lt;column&gt;</literal> element only) - </entry> - </row> - <row> - <entry><literal>default</literal></entry> - <entry>SQL expression</entry> - <entry> - specify a default value for the column - </entry> - </row> - <row> - <entry><literal>check</literal></entry> - <entry>SQL expression</entry> - <entry> - create an SQL check constraint on either column or table - </entry> - </row> - </tbody> - </tgroup> - </table> - - <para> - The <literal>&lt;comment&gt;</literal> element allows you to specify comments - for the generated schema. - </para> - - <programlisting><![CDATA[<class name="Customer" table="CurCust"> - <comment>Current customers only</comment> - ... -</class>]]></programlisting> - - <programlisting><![CDATA[<property name="balance"> - <column name="bal"> - <comment>Balance in USD</comment> - </column> -</property>]]></programlisting> - - <para> - This results in a <literal>comment on table</literal> or - <literal>comment on column</literal> statement in the generated - DDL (where supported). - </para> - - </sect2> - - <sect2 id="toolsetguide-s1-3" revision="2"> - <title>Running the tool</title> - - <para> - The <literal>SchemaExport</literal> tool writes a DDL script to standard out and/or - executes the DDL statements. - </para> - - <para> - <literal>java -cp </literal><emphasis>hibernate_classpaths</emphasis> - <literal>org.hibernate.tool.hbm2ddl.SchemaExport</literal> <emphasis>options mapping_files</emphasis> - </para> - - <table frame="topbot"> - <title><literal>SchemaExport</literal> Command Line Options</title> - <tgroup cols="2"> - <colspec colwidth="1.5*"/> - <colspec colwidth="2*"/> - <thead> - <row> - <entry>Option</entry> - <entry>Description</entry> - </row> - </thead> - <tbody> - <row> - <entry><literal>--quiet</literal></entry> - <entry>don't output the script to stdout</entry> - </row> - <row> - <entry><literal>--drop</literal></entry> - <entry>only drop the tables</entry> - </row> - <row> - <entry><literal>--create</literal></entry> - <entry>only create the tables</entry> - </row> - <row> - <entry><literal>--text</literal></entry> - <entry>don't export to the database</entry> - </row> - <row> - <entry><literal>--output=my_schema.ddl</literal></entry> - <entry>output the ddl script to a file</entry> - </row> - <row> - <entry><literal>--naming=eg.MyNamingStrategy</literal></entry> - <entry>select a <literal>NamingStrategy</literal></entry> - </row> - <row> - <entry><literal>--config=hibernate.cfg.xml</literal></entry> - <entry>read Hibernate configuration from an XML file</entry> - </row> - <row> - <entry><literal>--properties=hibernate.properties</literal></entry> - <entry>read database properties from a file</entry> - </row> - <row> - <entry><literal>--format</literal></entry> - <entry>format the generated SQL nicely in the script</entry> - </row> - <row> - <entry><literal>--delimiter=;</literal></entry> - <entry>set an end of line delimiter for the script</entry> - </row> - </tbody> - </tgroup> - </table> - - <para> - You may even embed <literal>SchemaExport</literal> in your application: - </para> - - <programlisting><![CDATA[Configuration cfg = ....; -new SchemaExport(cfg).create(false, true);]]></programlisting> - - </sect2> - - <sect2 id="toolsetguide-s1-4"> - <title>Properties</title> - - <para> - Database properties may be specified - </para> - - <itemizedlist spacing="compact"> - <listitem> - <para>as system properties with <literal>-D</literal><emphasis>&lt;property&gt;</emphasis></para> - </listitem> - <listitem> - <para>in <literal>hibernate.properties</literal></para> - </listitem> - <listitem> - <para>in a named properties file with <literal>--properties</literal></para> - </listitem> - </itemizedlist> - - <para> - The needed properties are: - </para> - - <table frame="topbot"> - <title>SchemaExport Connection Properties</title> - <tgroup cols="2"> - <colspec colwidth="1.5*"/> - <colspec colwidth="2*"/> - <thead> - <row> - <entry>Property Name</entry> - <entry>Description</entry> - </row> - </thead> - <tbody> - <row> - <entry><literal>hibernate.connection.driver_class</literal></entry> - <entry>jdbc driver class</entry> - </row> - <row> - <entry><literal>hibernate.connection.url</literal></entry> - <entry>jdbc url</entry> - </row> - <row> - <entry><literal>hibernate.connection.username</literal></entry> - <entry>database user</entry> - </row> - <row> - <entry><literal>hibernate.connection.password</literal></entry> - <entry>user password</entry> - </row> - <row> - <entry><literal>hibernate.dialect</literal></entry> - <entry>dialect</entry> - </row> - </tbody> - </tgroup> - </table> - - </sect2> - - <sect2 id="toolsetguide-s1-5"> - <title>Using Ant</title> - - <para> - You can call <literal>SchemaExport</literal> from your Ant build script: - </para> - - <programlisting><![CDATA[<target name="schemaexport"> - <taskdef name="schemaexport" - classname="org.hibernate.tool.hbm2ddl.SchemaExportTask" - classpathref="class.path"/> - - <schemaexport - properties="hibernate.properties" - quiet="no" - text="no" - drop="no" - delimiter=";" - output="schema-export.sql"> - <fileset dir="src"> - <include name="**/*.hbm.xml"/> - </fileset> - </schemaexport> -</target>]]></programlisting> - - </sect2> - - <sect2 id="toolsetguide-s1-6" revision="2"> - <title>Incremental schema updates</title> - - <para> - The <literal>SchemaUpdate</literal> tool will update an existing schema with "incremental" changes. - Note that <literal>SchemaUpdate</literal> depends heavily upon the JDBC metadata API, so it will - not work with all JDBC drivers. - </para> - - <para> - <literal>java -cp </literal><emphasis>hibernate_classpaths</emphasis> - <literal>org.hibernate.tool.hbm2ddl.SchemaUpdate</literal> <emphasis>options mapping_files</emphasis> - </para> - - <table frame="topbot"> - <title><literal>SchemaUpdate</literal> Command Line Options</title> - <tgroup cols="2"> - <colspec colwidth="1.5*"/> - <colspec colwidth="2*"/> - <thead> - <row> - <entry>Option</entry> - <entry>Description</entry> - </row> - </thead> - <tbody> - <row> - <entry><literal>--quiet</literal></entry> - <entry>don't output the script to stdout</entry> - </row> - <row> - <entry><literal>--text</literal></entry> - <entry>don't export the script to the database</entry> - </row> - <row> - <entry><literal>--naming=eg.MyNamingStrategy</literal></entry> - <entry>select a <literal>NamingStrategy</literal></entry> - </row> - <row> - <entry><literal>--properties=hibernate.properties</literal></entry> - <entry>read database properties from a file</entry> - </row> - <row> - <entry><literal>--config=hibernate.cfg.xml</literal></entry> - <entry>specify a <literal>.cfg.xml</literal> file</entry> - </row> - </tbody> - </tgroup> - </table> - - <para> - You may embed <literal>SchemaUpdate</literal> in your application: - </para> - - <programlisting><![CDATA[Configuration cfg = ....; -new SchemaUpdate(cfg).execute(false);]]></programlisting> - - </sect2> - - <sect2 id="toolsetguide-s1-7"> - <title>Using Ant for incremental schema updates</title> - - <para> - You can call <literal>SchemaUpdate</literal> from the Ant script: - </para> - - <programlisting><![CDATA[<target name="schemaupdate"> - <taskdef name="schemaupdate" - classname="org.hibernate.tool.hbm2ddl.SchemaUpdateTask" - classpathref="class.path"/> - - <schemaupdate - properties="hibernate.properties" - quiet="no"> - <fileset dir="src"> - <include name="**/*.hbm.xml"/> - </fileset> - </schemaupdate> -</target>]]></programlisting> - - </sect2> - - <sect2 id="toolsetguide-s1-8" revision="1"> - <title>Schema validation</title> - - <para> - The <literal>SchemaValidator</literal> tool will validate that the existing database schema "matches" - your mapping documents. Note that <literal>SchemaValidator</literal> depends heavily upon the JDBC - metadata API, so it will not work with all JDBC drivers. This tool is extremely useful for testing. - </para> - - <para> - <literal>java -cp </literal><emphasis>hibernate_classpaths</emphasis> - <literal>org.hibernate.tool.hbm2ddl.SchemaValidator</literal> <emphasis>options mapping_files</emphasis> - </para> - - <table frame="topbot"> - <title><literal>SchemaValidator</literal> Command Line Options</title> - <tgroup cols="2"> - <colspec colwidth="1.5*"/> - <colspec colwidth="2*"/> - <thead> - <row> - <entry>Option</entry> - <entry>Description</entry> - </row> - </thead> - <tbody> - <row> - <entry><literal>--naming=eg.MyNamingStrategy</literal></entry> - <entry>select a <literal>NamingStrategy</literal></entry> - </row> - <row> - <entry><literal>--properties=hibernate.properties</literal></entry> - <entry>read database properties from a file</entry> - </row> - <row> - <entry><literal>--config=hibernate.cfg.xml</literal></entry> - <entry>specify a <literal>.cfg.xml</literal> file</entry> - </row> - </tbody> - </tgroup> - </table> - - <para> - You may embed <literal>SchemaValidator</literal> in your application: - </para> - - <programlisting><![CDATA[Configuration cfg = ....; -new SchemaValidator(cfg).validate();]]></programlisting> - - </sect2> - - <sect2 id="toolsetguide-s1-9"> - <title>Using Ant for schema validation</title> - - <para> - You can call <literal>SchemaValidator</literal> from the Ant script: - </para> - - <programlisting><![CDATA[<target name="schemavalidate"> - <taskdef name="schemavalidator" - classname="org.hibernate.tool.hbm2ddl.SchemaValidatorTask" - classpathref="class.path"/> - - <schemavalidator - properties="hibernate.properties"> - <fileset dir="src"> - <include name="**/*.hbm.xml"/> - </fileset> - </schemavalidator> -</target>]]></programlisting> - - </sect2> - - </sect1> - -</chapter> - Deleted: core/trunk/documentation/envers/src/main/docbook/en-US/content/transactions.xml =================================================================== --- core/trunk/documentation/envers/src/main/docbook/en-US/content/transactions.xml 2008-11-04 17:31:01 UTC (rev 15499) +++ core/trunk/documentation/envers/src/main/docbook/en-US/content/transactions.xml 2008-11-04 17:31:43 UTC (rev 15500) @@ -1,1136 +0,0 @@ -<?xml version='1.0' encoding="UTF-8"?> -<!-- - ~ Hibernate, Relational Persistence for Idiomatic Java - ~ - ~ Copyright (c) 2008, Red Hat Middleware LLC or third-party contributors as - ~ indicated by the @author tags or express copyright attribution - ~ statements applied by the authors. All third-party contributions are - ~ distributed under license by Red Hat Middleware LLC. - ~ - ~ This copyrighted material is made available to anyone wishing to use, modify, - ~ copy, or redistribute it subject to the terms and conditions of the GNU - ~ Lesser General Public License, as published by the Free Software Foundation. - ~ - ~ This program is distributed in the hope that it will be useful, - ~ but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY - ~ or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License - ~ for more details. - ~ - ~ You should have received a copy of the GNU Lesser General Public License - ~ along with this distribution; if not, write to: - ~ Free Software Foundation, Inc. - ~ 51 Franklin Street, Fifth Floor - ~ Boston, MA 02110-1301 USA - --> - -<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd"> - -<chapter id="transactions" revision="2"> - <title>Transactions And Concurrency</title> - - <para> - The most important point about Hibernate and concurrency control is that it is very - easy to understand. Hibernate directly uses JDBC connections and JTA resources without - adding any additional locking behavior. We highly recommend you spend some time with the - JDBC, ANSI, and transaction isolation specification of your database management system. - </para> - - <para> - Hibernate does not lock objects in memory. Your application can expect the behavior as - defined by the isolation level of your database transactions. Note that thanks to the - <literal>Session</literal>, which is also a transaction-scoped cache, Hibernate - provides repeatable reads for lookup by identifier and entity queries (not - reporting queries that return scalar values). - </para> - - <para> - In addition to versioning for automatic optimistic concurrency control, Hibernate also - offers a (minor) API for pessimistic locking of rows, using the - <literal>SELECT FOR UPDATE</literal> syntax. Optimistic concurrency control and - this API are discussed later in this chapter. - </para> - - <para> - We start the discussion of concurrency control in Hibernate with the granularity of - <literal>Configuration</literal>, <literal>SessionFactory</literal>, and - <literal>Session</literal>, as well as database transactions and long conversations. - </para> - - <sect1 id="transactions-basics" revision="1"> - <title>Session and transaction scopes</title> - - <para> - A <literal>SessionFactory</literal> is an expensive-to-create, threadsafe object - intended to be shared by all application threads. It is created once, usually on - application startup, from a <literal>Configuration</literal> instance. - </para> - - <para> - A <literal>Session</literal> is an inexpensive, non-threadsafe object that should be - used once, for a single request, a conversation, single unit of work, and then discarded. - A <literal>Session</literal> will not obtain a JDBC <literal>Connection</literal> - (or a <literal>Datasource</literal>) unless it is needed, hence consume no - resources until used. - </para> - - <para> - To complete this picture you also have to think about database transactions. A - database transaction has to be as short as possible, to reduce lock contention in - the database. Long database transactions will prevent your application from scaling - to highly concurrent load. Hence, it is almost never good design to hold a - database transaction open during user think time, until the unit of work is - complete. - </para> - - <para> - What is the scope of a unit of work? Can a single Hibernate <literal>Session</literal> - span several database transactions or is this a one-to-one relationship of scopes? When - should you open and close a <literal>Session</literal> and how do you demarcate the - database transaction boundaries? - </para> - - <sect2 id="transactions-basics-uow" revision="1"> - <title>Unit of work</title> - - <para> - First, don't use the <emphasis>session-per-operation</emphasis> antipattern, that is, - don't open and close a <literal>Session</literal> for every simple database call in - a single thread! Of course, the same is true for database transactions. Database calls - in an application are made using a planned sequence, they are grouped into atomic - units of work. (Note that this also means that auto-commit after every single - SQL statement is useless in an application, this mode is intended for ad-hoc SQL - console work. Hibernate disables, or expects the application server to do so, - auto-commit mode immediately.) Database transactions are never optional, all - communication with a database has to occur inside a transaction, no matter if - you read or write data. As explained, auto-commit behavior for reading data - should be avoided, as many small transactions are unlikely to perform better than - one clearly defined unit of work. The latter is also much more maintainable - and extensible. - </para> - - <para> - The most common pattern in a multi-user client/server application is - <emphasis>session-per-request</emphasis>. In this model, a request from the client - is sent to the server (where the Hibernate persistence layer runs), a new Hibernate - <literal>Session</literal> is opened, and all database operations are executed in this unit - of work. Once the work has been completed (and the response for the client has been prepared), - the session is flushed and closed. You would also use a single database transaction to - serve the clients request, starting and committing it when you open and close the - <literal>Session</literal>. The relationship between the two is one-to-one and this - model is a perfect fit for many applications. - </para> - - <para> - The challenge lies in the implementation. Hibernate provides built-in management of - the "current session" to simplify this pattern. All you have to do is start a - transaction when a server request has to be processed, and end the transaction - before the response is sent to the client. You can do this in any way you - like, common solutions are <literal>ServletFilter</literal>, AOP interceptor with a - pointcut on the service methods, or a proxy/interception container. An EJB container - is a standardized way to implement cross-cutting aspects such as transaction - demarcation on EJB session beans, declaratively with CMT. If you decide to - use programmatic transaction demarcation, prefer the Hibernate <literal>Transaction</literal> - API shown later in this chapter, for ease of use and code portability. - </para> - - <para> - Your application code can access a "current session" to process the request - by simply calling <literal>sessionFactory.getCurrentSession()</literal> anywhere - and as often as needed. You will always get a <literal>Session</literal> scoped - to the current database transaction. This has to be configured for either - resource-local or JTA environments, see <xref linkend="architecture-current-session"/>. - </para> - - <para> - Sometimes it is convenient to extend the scope of a <literal>Session</literal> and - database transaction until the "view has been rendered". This is especially useful - in servlet applications that utilize a separate rendering phase after the request - has been processed. Extending the database transaction until view rendering is - complete is easy to do if you implement your own interceptor. However, it is not - easily doable if you rely on EJBs with container-managed transactions, as a - transaction will be completed when an EJB method returns, before rendering of any - view can start. See the Hibernate website and forum for tips and examples around - this <emphasis>Open Session in View</emphasis> pattern. - </para> - - </sect2> - - <sect2 id="transactions-basics-apptx" revision="1"> - <title>Long conversations</title> - - <para> - The session-per-request pattern is not the only useful concept you can use to design - units of work. Many business processes require a whole series of interactions with the user - interleaved with database accesses. In web and enterprise applications it is - not acceptable for a database transaction to span a user interaction. Consider the following - example: - </para> - - <itemizedlist> - <listitem> - <para> - The first screen of a dialog opens, the data seen by the user has been loaded in - a particular <literal>Session</literal> and database transaction. The user is free to - modify the objects. - </para> - </listitem> - <listitem> - <para> - The user clicks "Save" after 5 minutes and expects his modifications to be made - persistent; he also expects that he was the only person editing this information and - that no conflicting modification can occur. - </para> - </listitem> - </itemizedlist> - - <para> - We call this unit of work, from the point of view of the user, a long running - <emphasis>conversation</emphasis> (or <emphasis>application transaction</emphasis>). - There are many ways how you can implement this in your application. - </para> - - <para> - A first naive implementation might keep the <literal>Session</literal> and database - transaction open during user think time, with locks held in the database to prevent - concurrent modification, and to guarantee isolation and atomicity. This is of course - an anti-pattern, since lock contention would not allow the application to scale with - the number of concurrent users. - </para> - - <para> - Clearly, we have to use several database transactions to implement the conversation. - In this case, maintaining isolation of business processes becomes the - partial responsibility of the application tier. A single conversation - usually spans several database transactions. It will be atomic if only one of - these database transactions (the last one) stores the updated data, all others - simply read data (e.g. in a wizard-style dialog spanning several request/response - cycles). This is easier to implement than it might sound, especially if - you use Hibernate's features: - </para> - - <itemizedlist> - <listitem> - <para> - <emphasis>Automatic Versioning</emphasis> - Hibernate can do automatic - optimistic concurrency control for you, it can automatically detect - if a concurrent modification occurred during user think time. Usually - we only check at the end of the conversation. - </para> - </listitem> - <listitem> - <para> - <emphasis>Detached Objects</emphasis> - If you decide to use the already - discussed <emphasis>session-per-request</emphasis> pattern, all loaded instances - will be in detached state during user think time. Hibernate allows you to - reattach the objects and persist the modifications, the pattern is called - <emphasis>session-per-request-with-detached-objects</emphasis>. Automatic - versioning is used to isolate concurrent modifications. - </para> - </listitem> - <listitem> - <para> - <emphasis>Extended (or Long) Session</emphasis> - The Hibernate - <literal>Session</literal> may be disconnected from the underlying JDBC - connection after the database transaction has been committed, and reconnected - when a new client request occurs. This pattern is known as - <emphasis>session-per-conversation</emphasis> and makes - even reattachment unnecessary. Automatic versioning is used to isolate - concurrent modifications and the <literal>Session</literal> is usually - not allowed to be flushed automatically, but explicitly. - </para> - </listitem> - </itemizedlist> - - <para> - Both <emphasis>session-per-request-with-detached-objects</emphasis> and - <emphasis>session-per-conversation</emphasis> have advantages and disadvantages, - we discuss them later in this chapter in the context of optimistic concurrency control. - </para> - - </sect2> - - <sect2 id="transactions-basics-identity"> - <title>Considering object identity</title> - - <para> - An application may concurrently access the same persistent state in two - different <literal>Session</literal>s. However, an instance of a persistent class - is never shared between two <literal>Session</literal> instances. Hence there are - two different notions of identity: - </para> - - <variablelist spacing="compact"> - <varlistentry> - <term>Database Identity</term> - <listitem> - <para> - <literal>foo.getId().equals( bar.getId() )</literal> - </para> - </listitem> - </varlistentry> - <varlistentry> - <term>JVM Identity</term> - <listitem> - <para> - <literal>foo==bar</literal> - </para> - </listitem> - </varlistentry> - </variablelist> - - <para> - Then for objects attached to a <emphasis>particular</emphasis> <literal>Session</literal> - (i.e. in the scope of a <literal>Session</literal>) the two notions are equivalent, and - JVM identity for database identity is guaranteed by Hibernate. However, while the application - might concurrently access the "same" (persistent identity) business object in two different - sessions, the two instances will actually be "different" (JVM identity). Conflicts are - resolved using (automatic versioning) at flush/commit time, using an optimistic approach. - </para> - - <para> - This approach leaves Hibernate and the database to worry about concurrency; it also provides - the best scalability, since guaranteeing identity in single-threaded units of work only doesn't - need expensive locking or other means of synchronization. The application never needs to - synchronize on any business object, as long as it sticks to a single thread per - <literal>Session</literal>. Within a <literal>Session</literal> the application may safely use - <literal>==</literal> to compare objects. - </para> - - <para> - However, an application that uses <literal>==</literal> outside of a <literal>Session</literal>, - might see unexpected results. This might occur even in some unexpected places, for example, - if you put two detached instances into the same <literal>Set</literal>. Both might have the same - database identity (i.e. they represent the same row), but JVM identity is by definition not - guaranteed for instances in detached state. The developer has to override the <literal>equals()</literal> - and <literal>hashCode()</literal> methods in persistent classes and implement - his own notion of object equality. There is one caveat: Never use the database - identifier to implement equality, use a business key, a combination of unique, usually - immutable, attributes. The database identifier will change if a transient object is made - persistent. If the transient instance (usually together with detached instances) is held in a - <literal>Set</literal>, changing the hashcode breaks the contract of the <literal>Set</literal>. - Attributes for business keys don't have to be as stable as database primary keys, you only - have to guarantee stability as long as the objects are in the same <literal>Set</literal>. See - the Hibernate website for a more thorough discussion of this issue. Also note that this is not - a Hibernate issue, but simply how Java object identity and equality has to be implemented. - </para> - - </sect2> - - <sect2 id="transactions-basics-issues"> - <title>Common issues</title> - - <para> - Never use the anti-patterns <emphasis>session-per-user-session</emphasis> or - <emphasis>session-per-application</emphasis> (of course, there are rare exceptions to - this rule). Note that some of the following issues might also appear with the recommended - patterns, make sure you understand the implications before making a design decision: - </para> - - <itemizedlist> - <listitem> - <para> - A <literal>Session</literal> is not thread-safe. Things which are supposed to work - concurrently, like HTTP requests, session beans, or Swing workers, will cause race - conditions if a <literal>Session</literal> instance would be shared. If you keep your - Hibernate <literal>Session</literal> in your <literal>HttpSession</literal> (discussed - later), you should consider synchronizing access to your Http session. Otherwise, - a user that clicks reload fast enough may use the same <literal>Session</literal> in - two concurrently running threads. - </para> - </listitem> - <listitem> - <para> - An exception thrown by Hibernate means you have to rollback your database transaction - and close the <literal>Session</literal> immediately (discussed later in more detail). - If your <literal>Session</literal> is bound to the application, you have to stop - the application. Rolling back the database transaction doesn't put your business - objects back into the state they were at the start of the transaction. This means the - database state and the business objects do get out of sync. Usually this is not a - problem, because exceptions are not recoverable and you have to start over after - rollback anyway. - </para> - </listitem> - <listitem> - <para> - The <literal>Session</literal> caches every object that is in persistent state (watched - and checked for dirty state by Hibernate). This means it grows endlessly until you - get an OutOfMemoryException, if you keep it open for a long time or simply load too - much data. One solution for this is to call <literal>clear()</literal> and <literal>evict()</literal> - to manage the <literal>Session</literal> cache, but you most likely should consider a - Stored Procedure if you need mass data operations. Some solutions are shown in - <xref linkend="batch"/>. Keeping a <literal>Session</literal> open for the duration - of a user session also means a high probability of stale data. - </para> - </listitem> - </itemizedlist> - - </sect2> - - </sect1> - - <sect1 id="transactions-demarcation"> - <title>Database transaction demarcation</title> - - <para> - Database (or system) transaction boundaries are always necessary. No communication with - the database can occur outside of a database transaction (this seems to confuse many developers - who are used to the auto-commit mode). Always use clear transaction boundaries, even for - read-only operations. Depending on your isolation level and database capabilities this might not - be required but there is no downside if you always demarcate transactions explicitly. Certainly, - a single database transaction is going to perform better than many small transactions, even - for reading data. - </para> - - <para> - A Hibernate application can run in non-managed (i.e. standalone, simple Web- or Swing applications) - and managed J2EE environments. In a non-managed environment, Hibernate is usually responsible for - its own database connection pool. The application developer has to manually set transaction - boundaries, in other words, begin, commit, or rollback database transactions himself. A managed environment - usually provides container-managed transactions (CMT), with the transaction assembly defined declaratively - in deployment descriptors of EJB session beans, for example. Programmatic transaction demarcation is - then no longer necessary. - </para> - - <para> - However, it is often desirable to keep your persistence layer portable between non-managed - resource-local environments, and systems that can rely on JTA but use BMT instead of CMT. - In both cases you'd use programmatic transaction demarcation. Hibernate offers a wrapper - API called <literal>Transaction</literal> that translates into the native transaction system of - your deployment environment. This API is actually optional, but we strongly encourage its use - unless you are in a CMT session bean. - </para> - - <para> - Usually, ending a <literal>Session</literal> involves four distinct phases: - </para> - - <itemizedlist spacing="compact"> - <listitem> - <para> - flush the session - </para> - </listitem> - <listitem> - <para> - commit the transaction - </para> - </listitem> - <listitem> - <para> - close the session - </para> - </listitem> - <listitem> - <para> - handle exceptions - </para> - </listitem> - </itemizedlist> - - <para> - Flushing the session has been discussed earlier, we'll now have a closer look at transaction - demarcation and exception handling in both managed- and non-managed environments. - </para> - - - <sect2 id="transactions-demarcation-nonmanaged" revision="2"> - <title>Non-managed environment</title> - - <para> - If a Hibernate persistence layer runs in a non-managed environment, database connections - are usually handled by simple (i.e. non-DataSource) connection pools from which - Hibernate obtains connections as needed. The session/transaction handling idiom looks - like this: - </para> - - <programlisting><![CDATA[// Non-managed environment idiom -Session sess = factory.openSession(); -Transaction tx = null; -try { - tx = sess.beginTransaction(); - - // do some work - ... - - tx.commit(); -} -catch (RuntimeException e) { - if (tx != null) tx.rollback(); - throw e; // or display error message -} -finally { - sess.close(); -}]]></programlisting> - - <para> - You don't have to <literal>flush()</literal> the <literal>Session</literal> explicitly - - the call to <literal>commit()</literal> automatically triggers the synchronization (depending - upon the <link linkend="objectstate-flushing">FlushMode</link> for the session. - A call to <literal>close()</literal> marks the end of a session. The main implication - of <literal>close()</literal> is that the JDBC connection will be relinquished by the - session. This Java code is portable and runs in both non-managed and JTA environments. - </para> - - <para> - A much more flexible solution is Hibernate's built-in "current session" context - management, as described earlier: - </para> - - <programlisting><![CDATA[// Non-managed environment idiom with getCurrentSession() -try { - factory.getCurrentSession().beginTransaction(); - - // do some work - ... - - factory.getCurrentSession().getTransaction().commit(); -} -catch (RuntimeException e) { - factory.getCurrentSession().getTransaction().rollback(); - throw e; // or display error message -}]]></programlisting> - - <para> - You will very likely never see these code snippets in a regular application; - fatal (system) exceptions should always be caught at the "top". In other words, the - code that executes Hibernate calls (in the persistence layer) and the code that handles - <literal>RuntimeException</literal> (and usually can only clean up and exit) are in - different layers. The current context management by Hibernate can significantly - simplify this design, as all you need is access to a <literal>SessionFactory</literal>. - Exception handling is discussed later in this chapter. - </para> - - <para> - Note that you should select <literal>org.hibernate.transaction.JDBCTransactionFactory</literal> - (which is the default), and for the second example <literal>"thread"</literal> as your - <literal>hibernate.current_session_context_class</literal>. - </para> - - </sect2> - - <sect2 id="transactions-demarcation-jta" revision="3"> - <title>Using JTA</title> - - <para> - If your persistence layer runs in an application server (e.g. behind EJB session beans), - every datasource connection obtained by Hibernate will automatically be part of the global - JTA transaction. You can also install a standalone JTA implementation and use it without - EJB. Hibernate offers two strategies for JTA integration. - </para> - - <para> - If you use bean-managed transactions (BMT) Hibernate will tell the application server to start - and end a BMT transaction if you use the <literal>Transaction</literal> API. So, the - transaction management code is identical to the non-managed environment. - </para> - - <programlisting><![CDATA[// BMT idiom -Session sess = factory.openSession(); -Transaction tx = null; -try { - tx = sess.beginTransaction(); - - // do some work - ... - - tx.commit(); -} -catch (RuntimeException e) { - if (tx != null) tx.rollback(); - throw e; // or display error message -} -finally { - sess.close(); -}]]></programlisting> - - <para> - If you want to use a transaction-bound <literal>Session</literal>, that is, the - <literal>getCurrentSession()</literal> functionality for easy context propagation, - you will have to use the JTA <literal>UserTransaction</literal> API directly: - </para> - - <programlisting><![CDATA[// BMT idiom with getCurrentSession() -try { - UserTransaction tx = (UserTransaction)new InitialContext() - .lookup("java:comp/UserTransaction"); - - tx.begin(); - - // Do some work on Session bound to transaction - factory.getCurrentSession().load(...); - factory.getCurrentSession().persist(...); - - tx.commit(); -} -catch (RuntimeException e) { - tx.rollback(); - throw e; // or display error message -}]]></programlisting> - - <para> - With CMT, transaction demarcation is done in session bean deployment descriptors, not programmatically, - hence, the code is reduced to: - </para> - - <programlisting><![CDATA[// CMT idiom - Session sess = factory.getCurrentSession(); - - // do some work - ... -]]></programlisting> - - <para> - In a CMT/EJB even rollback happens automatically, since an unhandled <literal>RuntimeException</literal> - thrown by a session bean method tells the container to set the global transaction to rollback. - <emphasis>This means you do not need to use the Hibernate <literal>Transaction</literal> API at - all with BMT or CMT, and you get automatic propagation of the "current" Session bound to the - transaction.</emphasis> - </para> - - <para> - Note that you should choose <literal>org.hibernate.transaction.JTATransactionFactory</literal> - if you use JTA directly (BMT), and <literal>org.hibernate.transaction.CMTTransactionFactory</literal> - in a CMT session bean, when you configure Hibernate's transaction factory. Remember to also set - <literal>hibernate.transaction.manager_lookup_class</literal>. Furthermore, make sure - that your <literal>hibernate.current_session_context_class</literal> is either unset (backwards - compatibility), or set to <literal>"jta"</literal>. - </para> - - <para> - The <literal>getCurrentSession()</literal> operation has one downside in a JTA environment. - There is one caveat to the use of <literal>after_statement</literal> connection release - mode, which is then used by default. Due to a silly limitation of the JTA spec, it is not - possible for Hibernate to automatically clean up any unclosed <literal>ScrollableResults</literal> or - <literal>Iterator</literal> instances returned by <literal>scroll()</literal> or - <literal>iterate()</literal>. You <emphasis>must</emphasis> release the underlying database - cursor by calling <literal>ScrollableResults.close()</literal> or - <literal>Hibernate.close(Iterator)</literal> explicitly from a <literal>finally</literal> - block. (Of course, most applications can easily avoid using <literal>scroll()</literal> or - <literal>iterate()</literal> at all from the JTA or CMT code.) - </para> - - </sect2> - - <sect2 id="transactions-demarcation-exceptions"> - <title>Exception handling</title> - - <para> - If the <literal>Session</literal> throws an exception (including any - <literal>SQLException</literal>), you should immediately rollback the database - transaction, call <literal>Session.close()</literal> and discard the - <literal>Session</literal> instance. Certain methods of <literal>Session</literal> - will <emphasis>not</emphasis> leave the session in a consistent state. No - exception thrown by Hibernate can be treated as recoverable. Ensure that the - <literal>Session</literal> will be closed by calling <literal>close()</literal> - in a <literal>finally</literal> block. - </para> - - <para> - The <literal>HibernateException</literal>, which wraps most of the errors that - can occur in a Hibernate persistence layer, is an unchecked exception (it wasn't - in older versions of Hibernate). In our opinion, we shouldn't force the application - developer to catch an unrecoverable exception at a low layer. In most systems, unchecked - and fatal exceptions are handled in one of the first frames of the method call - stack (i.e. in higher layers) and an error message is presented to the application - user (or some other appropriate action is taken). Note that Hibernate might also throw - other unchecked exceptions which are not a <literal>HibernateException</literal>. These - are, again, not recoverable and appropriate action should be taken. - </para> - - <para> - Hibernate wraps <literal>SQLException</literal>s thrown while interacting with the database - in a <literal>JDBCException</literal>. In fact, Hibernate will attempt to convert the exception - into a more meaningful subclass of <literal>JDBCException</literal>. The underlying - <literal>SQLException</literal> is always available via <literal>JDBCException.getCause()</literal>. - Hibernate converts the <literal>SQLException</literal> into an appropriate - <literal>JDBCException</literal> subclass using the <literal>SQLExceptionConverter</literal> - attached to the <literal>SessionFactory</literal>. By default, the - <literal>SQLExceptionConverter</literal> is defined by the configured dialect; however, it is - also possible to plug in a custom implementation (see the javadocs for the - <literal>SQLExceptionConverterFactory</literal> class for details). The standard - <literal>JDBCException</literal> subtypes are: - </para> - - <itemizedlist spacing="compact"> - <listitem> - <para> - <literal>JDBCConnectionException</literal> - indicates an error - with the underlying JDBC communication. - </para> - </listitem> - <listitem> - <para> - <literal>SQLGrammarException</literal> - indicates a grammar - or syntax problem with the issued SQL. - </para> - </listitem> - <listitem> - <para> - <literal>ConstraintViolationException</literal> - indicates some - form of integrity constraint violation. - </para> - </listitem> - <listitem> - <para> - <literal>LockAcquisitionException</literal> - indicates an error - acquiring a lock level necessary to perform the requested operation. - </para> - </listitem> - <listitem> - <para> - <literal>GenericJDBCException</literal> - a generic exception - which did not fall into any of the other categories. - </para> - </listitem> - </itemizedlist> - - </sect2> - - <sect2 id="transactions-demarcation-timeout"> - <title>Transaction timeout</title> - - <para> - One extremely important feature provided by a managed environment like EJB - that is never provided for non-managed code is transaction timeout. Transaction - timeouts ensure that no misbehaving transaction can indefinitely tie up - resources while returning no response to the user. Outside a managed (JTA) - environment, Hibernate cannot fully provide this functionality. However, - Hibernate can at least control data access operations, ensuring that database - level deadlocks and queries with huge result sets are limited by a defined - timeout. In a managed environment, Hibernate can delegate transaction timeout - to JTA. This functionality is abstracted by the Hibernate - <literal>Transaction</literal> object. - </para> - - <programlisting><![CDATA[ -Session sess = factory.openSession(); -try { - //set transaction timeout to 3 seconds - sess.getTransaction().setTimeout(3); - sess.getTransaction().begin(); - - // do some work - ... - - sess.getTransaction().commit() -} -catch (RuntimeException e) { - sess.getTransaction().rollback(); - throw e; // or display error message -} -finally { - sess.close(); -}]]></programlisting> - - <para> - Note that <literal>setTimeout()</literal> may not be called in a CMT bean, - where transaction timeouts must be defined declaratively. - </para> - - </sect2> - - </sect1> - - <sect1 id="transactions-optimistic"> - <title>Optimistic concurrency control</title> - - <para> - The only approach that is consistent with high concurrency and high - scalability is optimistic concurrency control with versioning. Version - checking uses version numbers, or timestamps, to detect conflicting updates - (and to prevent lost updates). Hibernate provides for three possible approaches - to writing application code that uses optimistic concurrency. The use cases - we show are in the context of long conversations, but version checking - also has the benefit of preventing lost updates in single database transactions. - </para> - - <sect2 id="transactions-optimistic-manual"> - <title>Application version checking</title> - - <para> - In an implementation without much help from Hibernate, each interaction with the - database occurs in a new <literal>Session</literal> and the developer is responsible - for reloading all persistent instances from the database before manipulating them. - This approach forces the application to carry out its own version checking to ensure - conversation transaction isolation. This approach is the least efficient in terms of - database access. It is the approach most similar to entity EJBs. - </para> - - <programlisting><![CDATA[// foo is an instance loaded by a previous Session -session = factory.openSession(); -Transaction t = session.beginTransaction(); - -int oldVersion = foo.getVersion(); -session.load( foo, foo.getKey() ); // load the current state -if ( oldVersion != foo.getVersion() ) throw new StaleObjectStateException(); -foo.setProperty("bar"); - -t.commit(); -session.close();]]></programlisting> - - <para> - The <literal>version</literal> property is mapped using <literal>&lt;version&gt;</literal>, - and Hibernate will automatically increment it during flush if the entity is - dirty. - </para> - - <para> - Of course, if you are operating in a low-data-concurrency environment and don't - require version checking, you may use this approach and just skip the version - check. In that case, <emphasis>last commit wins</emphasis> will be the default - strategy for your long conversations. Keep in mind that this might - confuse the users of the application, as they might experience lost updates without - error messages or a chance to merge conflicting changes. - </para> - - <para> - Clearly, manual version checking is only feasible in very trivial circumstances - and not practical for most applications. Often not only single instances, but - complete graphs of modified objects have to be checked. Hibernate offers automatic - version checking with either an extended <literal>Session</literal> or detached instances - as the design paradigm. - </para> - - </sect2> - - <sect2 id="transactions-optimistic-longsession"> - <title>Extended session and automatic versioning</title> - - <para> - A single <literal>Session</literal> instance and its persistent instances are - used for the whole conversation, known as <emphasis>session-per-conversation</emphasis>. - Hibernate checks instance versions at flush time, throwing an exception if concurrent - modification is detected. It's up to the developer to catch and handle this exception - (common options are the opportunity for the user to merge changes or to restart the - business conversation with non-stale data). - </para> - - <para> - The <literal>Session</literal> is disconnected from any underlying JDBC connection - when waiting for user interaction. This approach is the most efficient in terms - of database access. The application need not concern itself with version checking or - with reattaching detached instances, nor does it have to reload instances in every - database transaction. - </para> - - <programlisting><![CDATA[// foo is an instance loaded earlier by the old session -Transaction t = session.beginTransaction(); // Obtain a new JDBC connection, start transaction - -foo.setProperty("bar"); - -session.flush(); // Only for last transaction in conversation -t.commit(); // Also return JDBC connection -session.close(); // Only for last transaction in conversation]]></programlisting> - <para> - The <literal>foo</literal> object still knows which <literal>Session</literal> it was - loaded in. Beginning a new database transaction on an old session obtains a new connection - and resumes the session. Committing a database transaction disconnects a session - from the JDBC connection and returns the connection to the pool. After reconnection, to - force a version check on data you aren't updating, you may call <literal>Session.lock()</literal> - with <literal>LockMode.READ</literal> on any objects that might have been updated by another - transaction. You don't need to lock any data that you <emphasis>are</emphasis> updating. - Usually you would set <literal>FlushMode.MANUAL</literal> on an extended <literal>Session</literal>, - so that only the last database transaction cycle is allowed to actually persist all - modifications made in this conversation. Hence, only this last database transaction - would include the <literal>flush()</literal> operation, and then also - <literal>close()</literal> the session to end the conversation. - </para> - - <para> - This pattern is problematic if the <literal>Session</literal> is too big to - be stored during user think time, e.g. an <literal>HttpSession</literal> should - be kept as small as possible. As the <literal>Session</literal> is also the - (mandatory) first-level cache and contains all loaded objects, we can probably - use this strategy only for a few request/response cycles. You should use a - <literal>Session</literal> only for a single conversation, as it will soon also - have stale data. - </para> - - <para> - (Note that earlier Hibernate versions required explicit disconnection and reconnection - of a <literal>Session</literal>. These methods are deprecated, as beginning and - ending a transaction has the same effect.) - </para> - - <para> - Also note that you should keep the disconnected <literal>Session</literal> close - to the persistence layer. In other words, use an EJB stateful session bean to - hold the <literal>Session</literal> in a three-tier environment, and don't transfer - it to the web layer (or even serialize it to a separate tier) to store it in the - <literal>HttpSession</literal>. - </para> - - <para> - The extended session pattern, or <emphasis>session-per-conversation</emphasis>, is - more difficult to implement with automatic current session context management. - You need to supply your own implementation of the <literal>CurrentSessionContext</literal> - for this, see the Hibernate Wiki for examples. - </para> - - </sect2> - - <sect2 id="transactions-optimistic-detached"> - <title>Detached objects and automatic versioning</title> - - <para> - Each interaction with the persistent store occurs in a new <literal>Session</literal>. - However, the same persistent instances are reused for each interaction with the database. - The application manipulates the state of detached instances originally loaded in another - <literal>Session</literal> and then reattaches them using <literal>Session.update()</literal>, - <literal>Session.saveOrUpdate()</literal>, or <literal>Session.merge()</literal>. - </para> - - <programlisting><![CDATA[// foo is an instance loaded by a previous Session -foo.setProperty("bar"); -session = factory.openSession(); -Transaction t = session.beginTransaction(); -session.saveOrUpdate(foo); // Use merge() if "foo" might have been loaded already -t.commit(); -session.close();]]></programlisting> - - <para> - Again, Hibernate will check instance versions during flush, throwing an - exception if conflicting updates occurred. - </para> - - <para> - You may also call <literal>lock()</literal> instead of <literal>update()</literal> - and use <literal>LockMode.READ</literal> (performing a version check, bypassing all - caches) if you are sure that the object has not been modified. - </para> - - </sect2> - - <sect2 id="transactions-optimistic-customizing"> - <title>Customizing automatic versioning</title> - - <para> - You may disable Hibernate's automatic version increment for particular properties and - collections by setting the <literal>optimistic-lock</literal> mapping attribute to - <literal>false</literal>. Hibernate will then no longer increment versions if the - property is dirty. - </para> - - <para> - Legacy database schemas are often static and can't be modified. Or, other applications - might also access the same database and don't know how to handle version numbers or - even timestamps. In both cases, versioning can't rely on a particular column in a table. - To force a version check without a version or timestamp property mapping, with a - comparison of the state of all fields in a row, turn on <literal>optimistic-lock="all"</literal> - in the <literal>&lt;class&gt;</literal> mapping. Note that this conceptually only works - if Hibernate can compare the old and new state, i.e. if you use a single long - <literal>Session</literal> and not session-per-request-with-detached-objects. - </para> - - <para> - Sometimes concurrent modification can be permitted as long as the changes that have been - made don't overlap. If you set <literal>optimistic-lock="dirty"</literal> when mapping the - <literal>&lt;class&gt;</literal>, Hibernate will only compare dirty fields during flush. - </para> - - <para> - In both cases, with dedicated version/timestamp columns or with full/dirty field - comparison, Hibernate uses a single <literal>UPDATE</literal> statement (with an - appropriate <literal>WHERE</literal> clause) per entity to execute the version check - and update the information. If you use transitive persistence to cascade reattachment - to associated entities, Hibernate might execute unnecessary updates. This is usually - not a problem, but <emphasis>on update</emphasis> triggers in the database might be - executed even when no changes have been made to detached instances. You can customize - this behavior by setting <literal>select-before-update="true"</literal> in the - <literal>&lt;class&gt;</literal> mapping, forcing Hibernate to <literal>SELECT</literal> - the instance to ensure that changes did actually occur, before updating the row. - </para> - - </sect2> - - </sect1> - - <sect1 id="transactions-locking"> - <title>Pessimistic Locking</title> - - <para> - It is not intended that users spend much time worrying about locking strategies. It's usually - enough to specify an isolation level for the JDBC connections and then simply let the - database do all the work. However, advanced users may sometimes wish to obtain - exclusive pessimistic locks, or re-obtain locks at the start of a new transaction. - </para> - - <para> - Hibernate will always use the locking mechanism of the database, never lock objects - in memory! - </para> - - <para> - The <literal>LockMode</literal> class defines the different lock levels that may be acquired - by Hibernate. A lock is obtained by the following mechanisms: - </para> - - <itemizedlist spacing="compact"> - <listitem> - <para> - <literal>LockMode.WRITE</literal> is acquired automatically when Hibernate updates or inserts - a row. - </para> - </listitem> - <listitem> - <para> - <literal>LockMode.UPGRADE</literal> may be acquired upon explicit user request using - <literal>SELECT ... FOR UPDATE</literal> on databases which support that syntax. - </para> - </listitem> - <listitem> - <para> - <literal>LockMode.UPGRADE_NOWAIT</literal> may be acquired upon explicit user request using a - <literal>SELECT ... FOR UPDATE NOWAIT</literal> under Oracle. - </para> - </listitem> - <listitem> - <para> - <literal>LockMode.READ</literal> is acquired automatically when Hibernate reads data - under Repeatable Read or Serializable isolation level. May be re-acquired by explicit user - request. - </para> - </listitem> - <listitem> - <para> - <literal>LockMode.NONE</literal> represents the absence of a lock. All objects switch to this - lock mode at the end of a <literal>Transaction</literal>. Objects associated with the session - via a call to <literal>update()</literal> or <literal>saveOrUpdate()</literal> also start out - in this lock mode. - </para> - </listitem> - </itemizedlist> - - <para> - The "explicit user request" is expressed in one of the following ways: - </para> - - <itemizedlist spacing="compact"> - <listitem> - <para> - A call to <literal>Session.load()</literal>, specifying a <literal>LockMode</literal>. - </para> - </listitem> - <listitem> - <para> - A call to <literal>Session.lock()</literal>. - </para> - </listitem> - <listitem> - <para> - A call to <literal>Query.setLockMode()</literal>. - </para> - </listitem> - </itemizedlist> - - <para> - If <literal>Session.load()</literal> is called with <literal>UPGRADE</literal> or - <literal>UPGRADE_NOWAIT</literal>, and the requested object was not yet loaded by - the session, the object is loaded using <literal>SELECT ... FOR UPDATE</literal>. - If <literal>load()</literal> is called for an object that is already loaded with - a less restrictive lock than the one requested, Hibernate calls - <literal>lock()</literal> for that object. - </para> - - <para> - <literal>Session.lock()</literal> performs a version number check if the specified lock - mode is <literal>READ</literal>, <literal>UPGRADE</literal> or - <literal>UPGRADE_NOWAIT</literal>. (In the case of <literal>UPGRADE</literal> or - <literal>UPGRADE_NOWAIT</literal>, <literal>SELECT ... FOR UPDATE</literal> is used.) - </para> - - <para> - If the database does not support the requested lock mode, Hibernate will use an appropriate - alternate mode (instead of throwing an exception). This ensures that applications will - be portable. - </para> - - </sect1> - - <sect1 id="transactions-connection-release"> - <title>Connection Release Modes</title> - - <para> - The legacy (2.x) behavior of Hibernate in regards to JDBC connection management - was that a <literal>Session</literal> would obtain a connection when it was first - needed and then hold unto that connection until the session was closed. - Hibernate 3.x introduced the notion of connection release modes to tell a session - how to handle its JDBC connections. Note that the following discussion is pertinent - only to connections provided through a configured <literal>ConnectionProvider</literal>; - user-supplied connections are outside the breadth of this discussion. The different - release modes are identified by the enumerated values of - <literal>org.hibernate.ConnectionReleaseMode</literal>: - </para> - - <itemizedlist spacing="compact"> - <listitem> - <para> - <literal>ON_CLOSE</literal> - is essentially the legacy behavior described above. The - Hibernate session obtains a connection when it first needs to perform some JDBC access - and holds unto that connection until the session is closed. - </para> - </listitem> - <listitem> - <para> - <literal>AFTER_TRANSACTION</literal> - says to release connections after a - <literal>org.hibernate.Transaction</literal> has completed. - </para> - </listitem> - <listitem> - <para> - <literal>AFTER_STATEMENT</literal> (also referred to as aggressive release) - says to - release connections after each and every statement execution. This aggressive releasing - is skipped if that statement leaves open resources associated with the given session; - currently the only situation where this occurs is through the use of - <literal>org.hibernate.ScrollableResults</literal>. - </para> - </listitem> - </itemizedlist> - - <para> - The configuration parameter <literal>hibernate.connection.release_mode</literal> is used - to specify which release mode to use. The possible values: - </para> - - <itemizedlist spacing="compact"> - <listitem> - <para> - <literal>auto</literal> (the default) - this choice delegates to the release mode - returned by the <literal>org.hibernate.transaction.TransactionFactory.getDefaultReleaseMode()</literal> - method. For JTATransactionFactory, this returns ConnectionReleaseMode.AFTER_STATEMENT; for - JDBCTransactionFactory, this returns ConnectionReleaseMode.AFTER_TRANSACTION. It is rarely - a good idea to change this default behavior as failures due to the value of this setting - tend to indicate bugs and/or invalid assumptions in user code. - </para> - </listitem> - <listitem> - <para> - <literal>on_close</literal> - says to use ConnectionReleaseMode.ON_CLOSE. This setting - is left for backwards compatibility, but its use is highly discouraged. - </para> - </listitem> - <listitem> - <para> - <literal>after_transaction</literal> - says to use ConnectionReleaseMode.AFTER_TRANSACTION. - This setting should not be used in JTA environments. Also note that with - ConnectionReleaseMode.AFTER_TRANSACTION, if a session is considered to be in auto-commit - mode connections will be released as if the release mode were AFTER_STATEMENT. - </para> - </listitem> - <listitem> - <para> - <literal>after_statement</literal> - says to use ConnectionReleaseMode.AFTER_STATEMENT. Additionally, - the configured <literal>ConnectionProvider</literal> is consulted to see if it supports this - setting (<literal>supportsAggressiveRelease()</literal>). If not, the release mode is reset - to ConnectionReleaseMode.AFTER_TRANSACTION. This setting is only safe in environments where - we can either re-acquire the same underlying JDBC connection each time we make a call into - <literal>ConnectionProvider.getConnection()</literal> or in auto-commit environments where - it does not matter whether we get back the same connection. - </para> - </listitem> - </itemizedlist> - - </sect1> - -</chapter> - Deleted: core/trunk/documentation/envers/src/main/docbook/en-US/content/tutorial.xml =================================================================== --- core/trunk/documentation/envers/src/main/docbook/en-US/content/tutorial.xml 2008-11-04 17:31:01 UTC (rev 15499) +++ core/trunk/documentation/envers/src/main/docbook/en-US/content/tutorial.xml 2008-11-04 17:31:43 UTC (rev 15500) @@ -1,1617 +0,0 @@ -<?xml version='1.0' encoding="UTF-8"?> -<!-- - ~ Hibernate, Relational Persistence for Idiomatic Java - ~ - ~ Copyright (c) 2008, Red Hat Middleware LLC or third-party contributors as - ~ indicated by the @author tags or express copyright attribution - ~ statements applied by the authors. All third-party contributions are - ~ distributed under license by Red Hat Middleware LLC. - ~ - ~ This copyrighted material is made available to anyone wishing to use, modify, - ~ copy, or redistribute it subject to the terms and conditions of the GNU - ~ Lesser General Public License, as published by the Free Software Foundation. - ~ - ~ This program is distributed in the hope that it will be useful, - ~ but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY - ~ or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License - ~ for more details. - ~ - ~ You should have received a copy of the GNU Lesser General Public License - ~ along with this distribution; if not, write to: - ~ Free Software Foundation, Inc. - ~ 51 Franklin Street, Fifth Floor - ~ Boston, MA 02110-1301 USA - --> - -<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [ - <!ENTITY mdash "-"> -]> - - <!-- todo : need searate sections, one for each tutorial --> - -<chapter id="tutorial"> - <title>Introduction to Hibernate</title> - - <sect1 id="tutorial-intro"> - <title>Preface</title> - - <para> - This chapter is an introduction to Hibernate by way of a tutorial, - intended for new users of Hibernate. We start with a simple - application using an in-memory database. We build the - application in small, easy to understand steps. The tutorial is - based on another, earlier one developed by Michael Gloegl. All - code is contained in the <filename>tutorials/web</filename> directory - of the project source. - </para> - - </sect1> - - <important> - <para> - This tutorial expects the user have knowledge of both Java and - SQL. If you are new or uncomfortable with either, it is advised - that you start with a good introduction to that technology prior - to attempting to learn Hibernate. It will save time and effort - in the long run. - </para> - </important> - - <note> - <para> - There is another tutorial/example application in the - <filename>/tutorials/eg</filename> directory of the project source. - That example is console based and as such would not have the - dependency on a servlet container to execute. The basic setup is - the same as the instructions below. - </para> - </note> - - <sect1 id="tutorial-firstapp"> - <title>Part 1 - The first Hibernate Application</title> - - <para> - Let's assume we need a small database application that can store - events we want to attend, and information about the host(s) of - these events. We will use an in-memory, Java database named HSQLDB - to avoid describing installation/setup of any particular database - servers. Feel free to tweak this tutorial to use whatever database - you feel comfortable using. - </para> - - <para> - The first thing we need to do is set up our development environment, - and specifically to setup all the required dependencies to Hibernate - as well as other libraries. Hibernate is built using Maven which - amongst other features provides <literal>dependecy management</literal>; - moreover it provides <emphasis>transitive</emphasis> - <literal>dependecy management</literal> which simply means that to use - Hibernate we can simply define our dependency on Hibernate, Hibernate - itself defines the dependencies it needs which then become transitive - dependencies of our project. - </para> - - <programlisting><![CDATA[. -<project xmlns="http://maven.apache.org/POM/4.0.0" - xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" - xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> - - ... - - <dependencies> - <dependency> - <groupId>${groupId}</groupId> - <artifactId>hibernate-core</artifactId> - </dependency> - - <!-- Because this is a web app, we also have a dependency on the servlet api. --> - <dependency> - <groupId>javax.servlet</groupId> - <artifactId>servlet-api</artifactId> - </dependency> - </dependencies> - -</project>]]></programlisting> - - <note> - <para> - Essentially we are describing here the - <filename>/tutorials/web/pom.xml</filename> file. See the - <ulink url="http://maven.org">Maven</ulink> site for more information. - </para> - </note> - - <tip> - <para> - While not strictly necessary, most IDEs have integration with Maven - to read these POM files and automatically set up a project for you - which can save lots of time and effort. - </para> - </tip> - - <para> - Next we create a class that represents the event we want to store in database. - </para> - - <sect2 id="tutorial-firstapp-firstclass"> - <title>The first class</title> - - <para> - Our first persistent class is a simple JavaBean class with some properties: - </para> - - <programlisting><![CDATA[package org.hibernate.tutorial.domain; - -import java.util.Date; - -public class Event { - private Long id; - - private String title; - private Date date; - - public Event() {} - - public Long getId() { - return id; - } - - private void setId(Long id) { - this.id = id; - } - - public Date getDate() { - return date; - } - - public void setDate(Date date) { - this.date = date; - } - - public String getTitle() { - return title; - } - - public void setTitle(String title) { - this.title = title; - } -}]]></programlisting> - - <para> - You can see that this class uses standard JavaBean naming conventions for property - getter and setter methods, as well as private visibility for the fields. This is - a recommended design - but not required. Hibernate can also access fields directly, - the benefit of accessor methods is robustness for refactoring. The no-argument - constructor is required to instantiate an object of this class through reflection. - </para> - - <para> - The <literal>id</literal> property holds a unique identifier value for a particular event. - All persistent entity classes (there are less important dependent classes as well) will need - such an identifier property if we want to use the full feature set of Hibernate. In fact, - most applications (esp. web applications) need to distinguish objects by identifier, so you - should consider this a feature rather than a limitation. However, we usually don't manipulate - the identity of an object, hence the setter method should be private. Only Hibernate will assign - identifiers when an object is saved. You can see that Hibernate can access public, private, - and protected accessor methods, as well as (public, private, protected) fields directly. The - choice is up to you and you can match it to fit your application design. - </para> - - <para> - The no-argument constructor is a requirement for all persistent classes; Hibernate - has to create objects for you, using Java Reflection. The constructor can be - private, however, package visibility is required for runtime proxy generation and - efficient data retrieval without bytecode instrumentation. - </para> - - <para> - Place this Java source file in a directory called <literal>src</literal> in the - development folder, and in its correct package. The directory should now look like this: - </para> - - <programlisting><![CDATA[. -+lib - <Hibernate and third-party libraries> -+src - +events - Event.java]]></programlisting> - - <para> - In the next step, we tell Hibernate about this persistent class. - </para> - - </sect2> - - <sect2 id="tutorial-firstapp-mapping"> - <title>The mapping file</title> - - <para> - Hibernate needs to know how to load and store objects of the persistent class. - This is where the Hibernate mapping file comes into play. The mapping file - tells Hibernate what table in the database it has to access, and what columns - in that table it should use. - </para> - - <para> - The basic structure of a mapping file looks like this: - </para> - - <programlisting><![CDATA[<?xml version="1.0"?> -<!DOCTYPE hibernate-mapping PUBLIC - "-//Hibernate/Hibernate Mapping DTD 3.0//EN" - "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> - -<hibernate-mapping> -[...] -</hibernate-mapping>]]></programlisting> - - <para> - Note that the Hibernate DTD is very sophisticated. You can use it for - auto-completion of XML mapping elements and attributes in your editor or - IDE. You also should open up the DTD file in your text editor - it's the - easiest way to get an overview of all elements and attributes and to see - the defaults, as well as some comments. Note that Hibernate will not - load the DTD file from the web, but first look it up from the classpath - of the application. The DTD file is included in <literal>hibernate3.jar</literal> - as well as in the <literal>src/</literal> directory of the Hibernate distribution. - </para> - - <para> - We will omit the DTD declaration in future examples to shorten the code. It is - of course not optional. - </para> - - <para> - Between the two <literal>hibernate-mapping</literal> tags, include a - <literal>class</literal> element. All persistent entity classes (again, there - might be dependent classes later on, which are not first-class entities) need - such a mapping, to a table in the SQL database: - </para> - - <programlisting><![CDATA[<hibernate-mapping> - - <class name="events.Event" table="EVENTS"> - - </class> - -</hibernate-mapping>]]></programlisting> - - <para> - So far we told Hibernate how to persist and load object of class <literal>Event</literal> - to the table <literal>EVENTS</literal>, each instance represented by a row in that table. - Now we continue with a mapping of the unique identifier property to the tables primary key. - In addition, as we don't want to care about handling this identifier, we configure Hibernate's - identifier generation strategy for a surrogate primary key column: - </para> - - <programlisting><![CDATA[<hibernate-mapping> - - <class name="events.Event" table="EVENTS"> - <id name="id" column="EVENT_ID"> - <generator class="native"/> - </id> - </class> - -</hibernate-mapping>]]></programlisting> - - <para> - The <literal>id</literal> element is the declaration of the identifier property, - <literal>name="id"</literal> declares the name of the Java property - - Hibernate will use the getter and setter methods to access the property. - The column attribute tells Hibernate which column of the - <literal>EVENTS</literal> table we use for this primary key. The nested - <literal>generator</literal> element specifies the identifier generation strategy, - in this case we used <literal>native</literal>, which picks the best strategy depending - on the configured database (dialect). Hibernate supports database generated, globally - unique, as well as application assigned identifiers (or any strategy you have written - an extension for). - </para> - - <para> - Finally we include declarations for the persistent properties of the class in - the mapping file. By default, no properties of the class are considered - persistent: - </para> - - <programlisting><![CDATA[ -<hibernate-mapping> - - <class name="events.Event" table="EVENTS"> - <id name="id" column="EVENT_ID"> - <generator class="native"/> - </id> - <property name="date" type="timestamp" column="EVENT_DATE"/> - <property name="title"/> - </class> - -</hibernate-mapping>]]></programlisting> - - <para> - Just as with the <literal>id</literal> element, the <literal>name</literal> - attribute of the <literal>property</literal> element tells Hibernate which getter - and setter methods to use. So, in this case, Hibernate will look for - <literal>getDate()/setDate()</literal>, as well as <literal>getTitle()/setTitle()</literal>. - </para> - - <para> - Why does the <literal>date</literal> property mapping include the - <literal>column</literal> attribute, but the <literal>title</literal> - doesn't? Without the <literal>column</literal> attribute Hibernate - by default uses the property name as the column name. This works fine for - <literal>title</literal>. However, <literal>date</literal> is a reserved - keyword in most database, so we better map it to a different name. - </para> - - <para> - The next interesting thing is that the <literal>title</literal> mapping also lacks - a <literal>type</literal> attribute. The types we declare and use in the mapping - files are not, as you might expect, Java data types. They are also not SQL - database types. These types are so called <emphasis>Hibernate mapping types</emphasis>, - converters which can translate from Java to SQL data types and vice versa. Again, - Hibernate will try to determine the correct conversion and mapping type itself if - the <literal>type</literal> attribute is not present in the mapping. In some cases this - automatic detection (using Reflection on the Java class) might not have the default you - expect or need. This is the case with the <literal>date</literal> property. Hibernate can't - know if the property (which is of <literal>java.util.Date</literal>) should map to a - SQL <literal>date</literal>, <literal>timestamp</literal>, or <literal>time</literal> column. - We preserve full date and time information by mapping the property with a - <literal>timestamp</literal> converter. - </para> - - <para> - This mapping file should be saved as <literal>Event.hbm.xml</literal>, right in - the directory next to the <literal>Event</literal> Java class source file. - The naming of mapping files can be arbitrary, however the <literal>hbm.xml</literal> - suffix is a convention in the Hibernate developer community. The directory structure - should now look like this: - </para> - - <programlisting><![CDATA[. -+lib - <Hibernate and third-party libraries> -+src - +events - Event.java - Event.hbm.xml]]></programlisting> - - <para> - We continue with the main configuration of Hibernate. - </para> - - </sect2> - - <sect2 id="tutorial-firstapp-configuration" revision="2"> - <title>Hibernate configuration</title> - - <para> - We now have a persistent class and its mapping file in place. It is time to configure - Hibernate. Before we do this, we will need a database. HSQL DB, a java-based SQL DBMS, - can be downloaded from the HSQL DB website(http://hsqldb.org/). Actually, you only need the <literal>hsqldb.jar</literal> - from this download. Place this file in the <literal>lib/</literal> directory of the - development folder. - </para> - - <para> - Create a directory called <literal>data</literal> in the root of the development directory - - this is where HSQL DB will store its data files. Now start the database by running - <literal>java -classpath ../lib/hsqldb.jar org.hsqldb.Server</literal> in this data directory. - You can see it start up and bind to a TCP/IP socket, this is where our application - will connect later. If you want to start with a fresh database during this tutorial, - shutdown HSQL DB (press <literal>CTRL + C</literal> in the window), delete all files in the - <literal>data/</literal> directory, and start HSQL DB again. - </para> - - <para> - Hibernate is the layer in your application which connects to this database, so it needs - connection information. The connections are made through a JDBC connection pool, which we - also have to configure. The Hibernate distribution contains several open source JDBC connection - pooling tools, but will use the Hibernate built-in connection pool for this tutorial. Note that - you have to copy the required library into your classpath and use different - connection pooling settings if you want to use a production-quality third party - JDBC pooling software. - </para> - - <para> - For Hibernate's configuration, we can use a simple <literal>hibernate.properties</literal> file, a - slightly more sophisticated <literal>hibernate.cfg.xml</literal> file, or even complete - programmatic setup. Most users prefer the XML configuration file: - </para> - - <programlisting><![CDATA[<?xml version='1.0' encoding='utf-8'?> -<!DOCTYPE hibernate-configuration PUBLIC - "-//Hibernate/Hibernate Configuration DTD 3.0//EN" - "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd"> - -<hibernate-configuration> - - <session-factory> - - <!-- Database connection settings --> - <property name="connection.driver_class">org.hsqldb.jdbcDriver</property> - <property name="connection.url">jdbc:hsqldb:hsql://localhost</property> - <property name="connection.username">sa</property> - <property name="connection.password"></property> - - <!-- JDBC connection pool (use the built-in) --> - <property name="connection.pool_size">1</property> - - <!-- SQL dialect --> - <property name="dialect">org.hibernate.dialect.HSQLDialect</property> - - <!-- Enable Hibernate's automatic session context management --> - <property name="current_session_context_class">thread</property> - - <!-- Disable the second-level cache --> - <property name="cache.provider_class">org.hibernate.cache.NoCacheProvider</property> - - <!-- Echo all executed SQL to stdout --> - <property name="show_sql">true</property> - - <!-- Drop and re-create the database schema on startup --> - <property name="hbm2ddl.auto">create</property> - - <mapping resource="events/Event.hbm.xml"/> - - </session-factory> - -</hibernate-configuration>]]></programlisting> - - <para> - Note that this XML configuration uses a different DTD. We configure - Hibernate's <literal>SessionFactory</literal> - a global factory responsible - for a particular database. If you have several databases, use several - <literal>&lt;session-factory&gt;</literal> configurations, usually in - several configuration files (for easier startup). - </para> - - <para> - The first four <literal>property</literal> elements contain the necessary - configuration for the JDBC connection. The dialect <literal>property</literal> - element specifies the particular SQL variant Hibernate generates. - Hibernate's automatic session management for persistence contexts will - come in handy as you will soon see. - The <literal>hbm2ddl.auto</literal> option turns on automatic generation of - database schemas - directly into the database. This can of course also be turned - off (by removing the config option) or redirected to a file with the help of - the <literal>SchemaExport</literal> Ant task. Finally, we add the mapping file(s) - for persistent classes to the configuration. - </para> - - <para> - Copy this file into the source directory, so it will end up in the - root of the classpath. Hibernate automatically looks for a file called - <literal>hibernate.cfg.xml</literal> in the root of the classpath, on startup. - </para> - - </sect2> - - <sect2 id="tutorial-firstapp-ant" revision="1"> - <title>Building with Ant</title> - - <para> - We'll now build the tutorial with Ant. You will need to have Ant installed - get - it from the <ulink url="http://ant.apache.org/bindownload.cgi">Ant download page</ulink>. - How to install Ant will not be covered here. Please refer to the - <ulink url="http://ant.apache.org/manual/index.html">Ant manual</ulink>. After you - have installed Ant, we can start to create the buildfile. It will be called - <literal>build.xml</literal> and placed directly in the development directory. - </para> - - <para> - A basic build file looks like this: - </para> - - <programlisting><![CDATA[<project name="hibernate-tutorial" default="compile"> - - <property name="sourcedir" value="${basedir}/src"/> - <property name="targetdir" value="${basedir}/bin"/> - <property name="librarydir" value="${basedir}/lib"/> - - <path id="libraries"> - <fileset dir="${librarydir}"> - <include name="*.jar"/> - </fileset> - </path> - - <target name="clean"> - <delete dir="${targetdir}"/> - <mkdir dir="${targetdir}"/> - </target> - - <target name="compile" depends="clean, copy-resources"> - <javac srcdir="${sourcedir}" - destdir="${targetdir}" - classpathref="libraries"/> - </target> - - <target name="copy-resources"> - <copy todir="${targetdir}"> - <fileset dir="${sourcedir}"> - <exclude name="**/*.java"/> - </fileset> - </copy> - </target> - -</project>]]></programlisting> - - <para> - This will tell Ant to add all files in the lib directory ending with <literal>.jar</literal> - to the classpath used for compilation. It will also copy all non-Java source files to the - target directory, e.g. configuration and Hibernate mapping files. If you now run Ant, you - should get this output: - </para> - - <programlisting><![CDATA[C:\hibernateTutorial\>ant -Buildfile: build.xml - -copy-resources: - [copy] Copying 2 files to C:\hibernateTutorial\bin - -compile: - [javac] Compiling 1 source file to C:\hibernateTutorial\bin - -BUILD SUCCESSFUL -Total time: 1 second ]]></programlisting> - - </sect2> - - <sect2 id="tutorial-firstapp-helpers" revision="3"> - <title>Startup and helpers</title> - - <para> - It's time to load and store some <literal>Event</literal> objects, but first - we have to complete the setup with some infrastructure code. We have to startup - Hibernate. This startup includes building a global <literal>SessionFactory</literal> - object and to store it somewhere for easy access in application code. - A <literal>SessionFactory</literal> can open up new <literal>Session</literal>'s. - A <literal>Session</literal> represents a single-threaded unit of work, the - <literal>SessionFactory</literal> is a thread-safe global object, instantiated once. - </para> - - <para> - We'll create a <literal>HibernateUtil</literal> helper class which takes care - of startup and makes accessing a <literal>SessionFactory</literal> convenient. - Let's have a look at the implementation: - </para> - - <programlisting><![CDATA[package util; - -import org.hibernate.*; -import org.hibernate.cfg.*; - -public class HibernateUtil { - - private static final SessionFactory sessionFactory; - - static { - try { - // Create the SessionFactory from hibernate.cfg.xml - sessionFactory = new Configuration().configure().buildSessionFactory(); - } catch (Throwable ex) { - // Make sure you log the exception, as it might be swallowed - System.err.println("Initial SessionFactory creation failed." + ex); - throw new ExceptionInInitializerError(ex); - } - } - - public static SessionFactory getSessionFactory() { - return sessionFactory; - } - -}]]></programlisting> - - <para> - This class does not only produce the global <literal>SessionFactory</literal> in - its static initializer (called once by the JVM when the class is loaded), but also - hides the fact that it uses a static singleton. It might as well lookup the - <literal>SessionFactory</literal> from JNDI in an application server. - </para> - - <para> - If you give the <literal>SessionFactory</literal> a name in your configuration - file, Hibernate will in fact try to bind it to JNDI after it has been built. - To avoid this code completely you could also use JMX deployment and let the - JMX-capable container instantiate and bind a <literal>HibernateService</literal> - to JNDI. These advanced options are discussed in the Hibernate reference - documentation. - </para> - - <para> - Place <literal>HibernateUtil.java</literal> in the development source directory, in - a package next to <literal>events</literal>: - </para> - - <programlisting><![CDATA[. -+lib - <Hibernate and third-party libraries> -+src - +events - Event.java - Event.hbm.xml - +util - HibernateUtil.java - hibernate.cfg.xml -+data -build.xml]]></programlisting> - - <para> - This should again compile without problems. We finally need to configure a logging - system - Hibernate uses commons logging and leaves you the choice between Log4j and - JDK 1.4 logging. Most developers prefer Log4j: copy <literal>log4j.properties</literal> - from the Hibernate distribution (it's in the <literal>etc/</literal> directory) to - your <literal>src</literal> directory, next to <literal>hibernate.cfg.xml</literal>. - Have a look at the example configuration and change the settings if you like to have - more verbose output. By default, only Hibernate startup message are shown on stdout. - </para> - - <para> - The tutorial infrastructure is complete - and we are ready to do some real work with - Hibernate. - </para> - - </sect2> - - <sect2 id="tutorial-firstapp-workingpersistence" revision="5"> - <title>Loading and storing objects</title> - - <para> - Finally, we can use Hibernate to load and store objects. We write an - <literal>EventManager</literal> class with a <literal>main()</literal> method: - </para> - - <programlisting><![CDATA[package events; -import org.hibernate.Session; - -import java.util.Date; - -import util.HibernateUtil; - -public class EventManager { - - public static void main(String[] args) { - EventManager mgr = new EventManager(); - - if (args[0].equals("store")) { - mgr.createAndStoreEvent("My Event", new Date()); - } - - HibernateUtil.getSessionFactory().close(); - } - - private void createAndStoreEvent(String title, Date theDate) { - - Session session = HibernateUtil.getSessionFactory().getCurrentSession(); - - session.beginTransaction(); - - Event theEvent = new Event(); - theEvent.setTitle(title); - theEvent.setDate(theDate); - - session.save(theEvent); - - session.getTransaction().commit(); - } - -}]]></programlisting> - - <para> - We create a new <literal>Event</literal> object, and hand it over to Hibernate. - Hibernate now takes care of the SQL and executes <literal>INSERT</literal>s - on the database. Let's have a look at the <literal>Session</literal> and - <literal>Transaction</literal>-handling code before we run this. - </para> - - <para> - A <literal>Session</literal> is a single unit of work. For now we'll keep things - simple and assume a one-to-one granularity between a Hibernate <literal>Session</literal> - and a database transaction. To shield our code from the actual underlying transaction - system (in this case plain JDBC, but it could also run with JTA) we use the - <literal>Transaction</literal> API that is available on the Hibernate <literal>Session</literal>. - </para> - - <para> - What does <literal>sessionFactory.getCurrentSession()</literal> do? First, you can call it - as many times and anywhere you like, once you get hold of your <literal>SessionFactory</literal> - (easy thanks to <literal>HibernateUtil</literal>). The <literal>getCurrentSession()</literal> - method always returns the "current" unit of work. Remember that we switched the configuration - option for this mechanism to "thread" in <literal>hibernate.cfg.xml</literal>? Hence, - the current unit of work is bound to the current Java thread that executes our application. - However, this is not the full picture, you also have to consider scope, when a unit of work - begins and when it ends. - </para> - - <para> - A <literal>Session</literal> begins when it is first needed, when the first call to - <literal>getCurrentSession()</literal> is made. It is then bound by Hibernate to the current - thread. When the transaction ends, either through commit or rollback, Hibernate automatically - unbinds the <literal>Session</literal> from the thread and closes it for you. If you call - <literal>getCurrentSession()</literal> again, you get a new <literal>Session</literal> and can - start a new unit of work. This <emphasis>thread-bound</emphasis> programming model is the most - popular way of using Hibernate, as it allows flexible layering of your code (transaction - demarcation code can be separated from data access code, we'll do this later in this tutorial). - </para> - - <para> - Related to the unit of work scope, should the Hibernate <literal>Session</literal> be used to - execute one or several database operations? The above example uses one <literal>Session</literal> - for one operation. This is pure coincidence, the example is just not complex enough to show any - other approach. The scope of a Hibernate <literal>Session</literal> is flexible but you should - never design your application to use a new Hibernate <literal>Session</literal> for - <emphasis>every</emphasis> database operation. So even if you see it a few more times in - the following (very trivial) examples, consider <emphasis>session-per-operation</emphasis> - an anti-pattern. A real (web) application is shown later in this tutorial. - </para> - - <para> - Have a look at <xref linkend="transactions"/> for more information - about transaction handling and demarcation. We also skipped any error handling and - rollback in the previous example. - </para> - - <para> - To run this first routine we have to add a callable target to the Ant build file: - </para> - - <programlisting><![CDATA[<target name="run" depends="compile"> - <java fork="true" classname="events.EventManager" classpathref="libraries"> - <classpath path="${targetdir}"/> - <arg value="${action}"/> - </java> -</target>]]></programlisting> - - <para> - The value of the <literal>action</literal> argument is set on the command line when - calling the target: - </para> - - <programlisting><![CDATA[C:\hibernateTutorial\>ant run -Daction=store]]></programlisting> - - <para> - You should see, after compilation, Hibernate starting up and, depending on your - configuration, lots of log output. At the end you will find the following line: - </para> - - <programlisting><![CDATA[[java] Hibernate: insert into EVENTS (EVENT_DATE, title, EVENT_ID) values (?, ?, ?)]]></programlisting> - - <para> - This is the <literal>INSERT</literal> executed by Hibernate, the question marks - represent JDBC bind parameters. To see the values bound as arguments, or to reduce - the verbosity of the log, check your <literal>log4j.properties</literal>. - </para> - - <para> - Now we'd like to list stored events as well, so we add an option to the main method: - </para> - - <programlisting><![CDATA[if (args[0].equals("store")) { - mgr.createAndStoreEvent("My Event", new Date()); -} -else if (args[0].equals("list")) { - List events = mgr.listEvents(); - for (int i = 0; i < events.size(); i++) { - Event theEvent = (Event) events.get(i); - System.out.println("Event: " + theEvent.getTitle() + - " Time: " + theEvent.getDate()); - } -}]]></programlisting> - - <para> - We also add a new <literal>listEvents() method</literal>: - </para> - - <programlisting><![CDATA[private List listEvents() { - - Session session = HibernateUtil.getSessionFactory().getCurrentSession(); - - session.beginTransaction(); - - List result = session.createQuery("from Event").list(); - - session.getTransaction().commit(); - - return result; -}]]></programlisting> - - <para> - What we do here is use an HQL (Hibernate Query Language) query to load all existing - <literal>Event</literal> objects from the database. Hibernate will generate the - appropriate SQL, send it to the database and populate <literal>Event</literal> objects - with the data. You can create more complex queries with HQL, of course. - </para> - - <para> - Now, to execute and test all of this, follow these steps: - </para> - - <itemizedlist> - <listitem> - <para> - Run <literal>ant run -Daction=store</literal> to store something into the database - and, of course, to generate the database schema before through hbm2ddl. - </para> - </listitem> - <listitem> - <para> - Now disable hbm2ddl by commenting out the property in your <literal>hibernate.cfg.xml</literal> - file. Usually you only leave it turned on in continuous unit testing, but another - run of hbm2ddl would <emphasis>drop</emphasis> everything you have stored - the - <literal>create</literal> configuration setting actually translates into "drop all - tables from the schema, then re-create all tables, when the SessionFactory is build". - </para> - </listitem> - </itemizedlist> - - <para> - If you now call Ant with <literal>-Daction=list</literal>, you should see the events - you have stored so far. You can of course also call the <literal>store</literal> action a few - times more. - </para> - - <para> - Note: Most new Hibernate users fail at this point and we see questions about - <emphasis>Table not found</emphasis> error messages regularly. However, if you follow the - steps outlined above you will not have this problem, as hbm2ddl creates the database - schema on the first run, and subsequent application restarts will use this schema. If - you change the mapping and/or database schema, you have to re-enable hbm2ddl once again. - </para> - - </sect2> - - </sect1> - - <sect1 id="tutorial-associations"> - <title>Part 2 - Mapping associations</title> - - <para> - We mapped a persistent entity class to a table. Let's build on this and add some class associations. - First we'll add people to our application, and store a list of events they participate in. - </para> - - <sect2 id="tutorial-associations-mappinguser" revision="1"> - <title>Mapping the Person class</title> - - <para> - The first cut of the <literal>Person</literal> class is simple: - </para> - - <programlisting><![CDATA[package events; - -public class Person { - - private Long id; - private int age; - private String firstname; - private String lastname; - - public Person() {} - - // Accessor methods for all properties, private setter for 'id' - -}]]></programlisting> - - <para> - Create a new mapping file called <literal>Person.hbm.xml</literal> (don't forget the - DTD reference at the top): - </para> - - <programlisting><![CDATA[<hibernate-mapping> - - <class name="events.Person" table="PERSON"> - <id name="id" column="PERSON_ID"> - <generator class="native"/> - </id> - <property name="age"/> - <property name="firstname"/> - <property name="lastname"/> - </class> - -</hibernate-mapping>]]></programlisting> - - <para> - Finally, add the new mapping to Hibernate's configuration: - </para> - - <programlisting><![CDATA[<mapping resource="events/Event.hbm.xml"/> -<mapping resource="events/Person.hbm.xml"/>]]></programlisting> - - <para> - We'll now create an association between these two entities. Obviously, persons - can participate in events, and events have participants. The design questions - we have to deal with are: directionality, multiplicity, and collection - behavior. - </para> - - </sect2> - - <sect2 id="tutorial-associations-unidirset" revision="3"> - <title>A unidirectional Set-based association</title> - - <para> - We'll add a collection of events to the <literal>Person</literal> class. That way we can - easily navigate to the events for a particular person, without executing an explicit query - - by calling <literal>aPerson.getEvents()</literal>. We use a Java collection, a <literal>Set</literal>, - because the collection will not contain duplicate elements and the ordering is not relevant for us. - </para> - - <para> - We need a unidirectional, many-valued associations, implemented with a <literal>Set</literal>. - Let's write the code for this in the Java classes and then map it: - </para> - - <programlisting><![CDATA[public class Person { - - private Set events = new HashSet(); - - public Set getEvents() { - return events; - } - - public void setEvents(Set events) { - this.events = events; - } -}]]></programlisting> - - <para> - Before we map this association, think about the other side. Clearly, we could just keep this - unidirectional. Or, we could create another collection on the <literal>Event</literal>, if we - want to be able to navigate it bi-directional, i.e. <literal>anEvent.getParticipants()</literal>. - This is not necessary, from a functional perspective. You could always execute an explicit query - to retrieve the participants for a particular event. This is a design choice left to you, but what - is clear from this discussion is the multiplicity of the association: "many" valued on both sides, - we call this a <emphasis>many-to-many</emphasis> association. Hence, we use Hibernate's - many-to-many mapping: - </para> - - <programlisting><![CDATA[<class name="events.Person" table="PERSON"> - <id name="id" column="PERSON_ID"> - <generator class="native"/> - </id> - <property name="age"/> - <property name="firstname"/> - <property name="lastname"/> - - <set name="events" table="PERSON_EVENT"> - <key column="PERSON_ID"/> - <many-to-many column="EVENT_ID" class="events.Event"/> - </set> - -</class>]]></programlisting> - - <para> - Hibernate supports all kinds of collection mappings, a <literal>&lt;set&gt;</literal> being most - common. For a many-to-many association (or <emphasis>n:m</emphasis> entity relationship), an - association table is needed. Each row in this table represents a link between a person and an event. - The table name is configured with the <literal>table</literal> attribute of the <literal>set</literal> - element. The identifier column name in the association, for the person's side, is defined with the - <literal>&lt;key&gt;</literal> element, the column name for the event's side with the - <literal>column</literal> attribute of the <literal>&lt;many-to-many&gt;</literal>. You also - have to tell Hibernate the class of the objects in your collection (correct: the class on the - other side of the collection of references). - </para> - - <para> - The database schema for this mapping is therefore: - </para> - - <programlisting><![CDATA[ - _____________ __________________ - | | | | _____________ - | EVENTS | | PERSON_EVENT | | | - |_____________| |__________________| | PERSON | - | | | | |_____________| - | *EVENT_ID | <--> | *EVENT_ID | | | - | EVENT_DATE | | *PERSON_ID | <--> | *PERSON_ID | - | TITLE | |__________________| | AGE | - |_____________| | FIRSTNAME | - | LASTNAME | - |_____________| - ]]></programlisting> - - </sect2> - - <sect2 id="tutorial-associations-working" revision="2"> - <title>Working the association</title> - - <para> - Let's bring some people and events together in a new method in <literal>EventManager</literal>: - </para> - - <programlisting><![CDATA[private void addPersonToEvent(Long personId, Long eventId) { - - Session session = HibernateUtil.getSessionFactory().getCurrentSession(); - session.beginTransaction(); - - Person aPerson = (Person) session.load(Person.class, personId); - Event anEvent = (Event) session.load(Event.class, eventId); - - aPerson.getEvents().add(anEvent); - - session.getTransaction().commit(); -}]]></programlisting> - - <para> - After loading a <literal>Person</literal> and an <literal>Event</literal>, simply - modify the collection using the normal collection methods. As you can see, there is no explicit call - to <literal>update()</literal> or <literal>save()</literal>, Hibernate automatically - detects that the collection has been modified and needs to be updated. This is called <emphasis>automatic - dirty checking</emphasis>, and you can also try it by modifying the name or the date property of - any of your objects. As long as they are in <emphasis>persistent</emphasis> state, that is, bound - to a particular Hibernate <literal>Session</literal> (i.e. they have been just loaded or saved in - a unit of work), Hibernate monitors any changes and executes SQL in a write-behind fashion. The - process of synchronizing the memory state with the database, usually only at the end of a unit of - work, is called <emphasis>flushing</emphasis>. In our code, the unit of work ends with a commit - (or rollback) of the database transaction - as defined by the <literal>thread</literal> configuration - option for the <literal>CurrentSessionContext</literal> class. - </para> - - <para> - You might of course load person and event in different units of work. Or you modify an object - outside of a <literal>Session</literal>, when it is not in persistent state (if it was persistent - before, we call this state <emphasis>detached</emphasis>). You can even modify a collection when - it is detached: - </para> - - <programlisting><![CDATA[private void addPersonToEvent(Long personId, Long eventId) { - - Session session = HibernateUtil.getSessionFactory().getCurrentSession(); - session.beginTransaction(); - - Person aPerson = (Person) session - .createQuery("select p from Person p left join fetch p.events where p.id = :pid") - .setParameter("pid", personId) - .uniqueResult(); // Eager fetch the collection so we can use it detached - - Event anEvent = (Event) session.load(Event.class, eventId); - - session.getTransaction().commit(); - - // End of first unit of work - - aPerson.getEvents().add(anEvent); // aPerson (and its collection) is detached - - // Begin second unit of work - - Session session2 = HibernateUtil.getSessionFactory().getCurrentSession(); - session2.beginTransaction(); - - session2.update(aPerson); // Reattachment of aPerson - - session2.getTransaction().commit(); -}]]></programlisting> - - <para> - The call to <literal>update</literal> makes a detached object persistent again, you could - say it binds it to a new unit of work, so any modifications you made to it while detached - can be saved to the database. This includes any modifications (additions/deletions) you - made to a collection of that entity object. - </para> - - <para> - Well, this is not much use in our current situation, but it's an important concept you can - design into your own application. For now, complete this exercise by adding a new action - to the <literal>EventManager</literal>'s main method and call it from the command line. If - you need the identifiers of a person and an event - the <literal>save()</literal> method - returns it (you might have to modify some of the previous methods to return that identifier): - </para> - - <programlisting><![CDATA[else if (args[0].equals("addpersontoevent")) { - Long eventId = mgr.createAndStoreEvent("My Event", new Date()); - Long personId = mgr.createAndStorePerson("Foo", "Bar"); - mgr.addPersonToEvent(personId, eventId); - System.out.println("Added person " + personId + " to event " + eventId); -}]]></programlisting> - - <para> - This was an example of an association between two equally important classes, two entities. - As mentioned earlier, there are other classes and types in a typical model, usually "less - important". Some you have already seen, like an <literal>int</literal> or a <literal>String</literal>. - We call these classes <emphasis>value types</emphasis>, and their instances <emphasis>depend</emphasis> - on a particular entity. Instances of these types don't have their own identity, nor are they - shared between entities (two persons don't reference the same <literal>firstname</literal> - object, even if they have the same first name). Of course, value types can not only be found in - the JDK (in fact, in a Hibernate application all JDK classes are considered value types), but - you can also write dependent classes yourself, <literal>Address</literal> or <literal>MonetaryAmount</literal>, - for example. - </para> - - <para> - You can also design a collection of value types. This is conceptually very different from a - collection of references to other entities, but looks almost the same in Java. - </para> - - </sect2> - - <sect2 id="tutorial-associations-valuecollections"> - <title>Collection of values</title> - - <para> - We add a collection of value typed objects to the <literal>Person</literal> entity. We want to - store email addresses, so the type we use is <literal>String</literal>, and the collection is - again a <literal>Set</literal>: - </para> - <programlisting><![CDATA[private Set emailAddresses = new HashSet(); - -public Set getEmailAddresses() { - return emailAddresses; -} - -public void setEmailAddresses(Set emailAddresses) { - this.emailAddresses = emailAddresses; -}]]></programlisting> - - <para> - The mapping of this <literal>Set</literal>: - </para> - - <programlisting><![CDATA[<set name="emailAddresses" table="PERSON_EMAIL_ADDR"> - <key column="PERSON_ID"/> - <element type="string" column="EMAIL_ADDR"/> -</set>]]></programlisting> - - <para> - The difference compared with the earlier mapping is the <literal>element</literal> part, which tells Hibernate that the collection - does not contain references to another entity, but a collection of elements of type - <literal>String</literal> (the lowercase name tells you it's a Hibernate mapping type/converter). - Once again, the <literal>table</literal> attribute of the <literal>set</literal> element determines - the table name for the collection. The <literal>key</literal> element defines the foreign-key column - name in the collection table. The <literal>column</literal> attribute in the <literal>element</literal> - element defines the column name where the <literal>String</literal> values will actually be stored. - </para> - - <para> - Have a look at the updated schema: - </para> - - <programlisting><![CDATA[ - _____________ __________________ - | | | | _____________ - | EVENTS | | PERSON_EVENT | | | ___________________ - |_____________| |__________________| | PERSON | | | - | | | | |_____________| | PERSON_EMAIL_ADDR | - | *EVENT_ID | <--> | *EVENT_ID | | | |___________________| - | EVENT_DATE | | *PERSON_ID | <--> | *PERSON_ID | <--> | *PERSON_ID | - | TITLE | |__________________| | AGE | | *EMAIL_ADDR | - |_____________| | FIRSTNAME | |___________________| - | LASTNAME | - |_____________| - ]]></programlisting> - - <para> - You can see that the primary key of the collection table is in fact a composite key, - using both columns. This also implies that there can't be duplicate email addresses - per person, which is exactly the semantics we need for a set in Java. - </para> - - <para> - You can now try and add elements to this collection, just like we did before by - linking persons and events. It's the same code in Java: - </para> - - <programlisting><![CDATA[private void addEmailToPerson(Long personId, String emailAddress) { - - Session session = HibernateUtil.getSessionFactory().getCurrentSession(); - session.beginTransaction(); - - Person aPerson = (Person) session.load(Person.class, personId); - - // The getEmailAddresses() might trigger a lazy load of the collection - aPerson.getEmailAddresses().add(emailAddress); - - session.getTransaction().commit(); -}]]></programlisting> - - <para> - This time we didn't use a <emphasis>fetch</emphasis> query to initialize the collection. - Hence, the call to its getter method will trigger an additional select to initialize - it, so we can add an element to it. Monitor the SQL log and try to optimize this with - an eager fetch. - </para> - - </sect2> - - <sect2 id="tutorial-associations-bidirectional" revision="1"> - <title>Bi-directional associations</title> - - <para> - Next we are going to map a bi-directional association - making the association between - person and event work from both sides in Java. Of course, the database schema doesn't - change, we still have many-to-many multiplicity. A relational database is more flexible - than a network programming language, so it doesn't need anything like a navigation - direction - data can be viewed and retrieved in any possible way. - </para> - - <para> - First, add a collection of participants to the <literal>Event</literal> Event class: - </para> - - <programlisting><![CDATA[private Set participants = new HashSet(); - -public Set getParticipants() { - return participants; -} - -public void setParticipants(Set participants) { - this.participants = participants; -}]]></programlisting> - - <para> - Now map this side of the association too, in <literal>Event.hbm.xml</literal>. - </para> - - <programlisting><![CDATA[<set name="participants" table="PERSON_EVENT" inverse="true"> - <key column="EVENT_ID"/> - <many-to-many column="PERSON_ID" class="events.Person"/> -</set>]]></programlisting> - - <para> - As you see, these are normal <literal>set</literal> mappings in both mapping documents. - Notice that the column names in <literal>key</literal> and <literal>many-to-many</literal> are - swapped in both mapping documents. The most important addition here is the - <literal>inverse="true"</literal> attribute in the <literal>set</literal> element of the - <literal>Event</literal>'s collection mapping. - </para> - - <para> - What this means is that Hibernate should take the other side - the <literal>Person</literal> class - - when it needs to find out information about the link between the two. This will be a lot easier to - understand once you see how the bi-directional link between our two entities is created . - </para> - - </sect2> - - <sect2 id="tutorial-associations-usingbidir"> - <title>Working bi-directional links</title> - - <para> - First, keep in mind that Hibernate does not affect normal Java semantics. How did we create a - link between a <literal>Person</literal> and an <literal>Event</literal> in the unidirectional - example? We added an instance of <literal>Event</literal> to the collection of event references, - of an instance of <literal>Person</literal>. So, obviously, if we want to make this link working - bi-directional, we have to do the same on the other side - adding a <literal>Person</literal> - reference to the collection in an <literal>Event</literal>. This "setting the link on both sides" - is absolutely necessary and you should never forget doing it. - </para> - - <para> - Many developers program defensively and create link management methods to - correctly set both sides, e.g. in <literal>Person</literal>: - </para> - - <programlisting><![CDATA[protected Set getEvents() { - return events; -} - -protected void setEvents(Set events) { - this.events = events; -} - -public void addToEvent(Event event) { - this.getEvents().add(event); - event.getParticipants().add(this); -} - -public void removeFromEvent(Event event) { - this.getEvents().remove(event); - event.getParticipants().remove(this); -}]]></programlisting> - - <para> - Notice that the get and set methods for the collection are now protected - this allows classes in the - same package and subclasses to still access the methods, but prevents everybody else from messing - with the collections directly (well, almost). You should probably do the same with the collection - on the other side. - </para> - - <para> - What about the <literal>inverse</literal> mapping attribute? For you, and for Java, a bi-directional - link is simply a matter of setting the references on both sides correctly. Hibernate however doesn't - have enough information to correctly arrange SQL <literal>INSERT</literal> and <literal>UPDATE</literal> - statements (to avoid constraint violations), and needs some help to handle bi-directional associations - properly. Making one side of the association <literal>inverse</literal> tells Hibernate to basically - ignore it, to consider it a <emphasis>mirror</emphasis> of the other side. That's all that is necessary - for Hibernate to work out all of the issues when transformation a directional navigation model to - a SQL database schema. The rules you have to remember are straightforward: All bi-directional associations - need one side as <literal>inverse</literal>. In a one-to-many association it has to be the many-side, - in many-to-many association you can pick either side, there is no difference. - </para> - - </sect2> - - </sect1> - - <sect1 id="tutorial-webapp"> - <title>Part 3 - The EventManager web application</title> - - <para> - Let's turn the following discussion into a small web application... - </para> - - <para> - A Hibernate web application uses <literal>Session</literal> and <literal>Transaction</literal> - almost like a standalone application. However, some common patterns are useful. We now write - an <literal>EventManagerServlet</literal>. This servlet can list all events stored in the - database, and it provides an HTML form to enter new events. - </para> - - <sect2 id="tutorial-webapp-servlet" revision="2"> - <title>Writing the basic servlet</title> - - <para> - Create a new class in your source directory, in the <literal>events</literal> - package: - </para> - - <programlisting><![CDATA[package events; - -// Imports - -public class EventManagerServlet extends HttpServlet { - - // Servlet code -}]]></programlisting> - - <para> - The servlet handles HTTP <literal>GET</literal> requests only, hence, the method - we implement is <literal>doGet()</literal>: - </para> - - <programlisting><![CDATA[protected void doGet(HttpServletRequest request, - HttpServletResponse response) - throws ServletException, IOException { - - SimpleDateFormat dateFormatter = new SimpleDateFormat("dd.MM.yyyy"); - - try { - // Begin unit of work - HibernateUtil.getSessionFactory() - .getCurrentSession().beginTransaction(); - - // Process request and render page... - - // End unit of work - HibernateUtil.getSessionFactory() - .getCurrentSession().getTransaction().commit(); - - } catch (Exception ex) { - HibernateUtil.getSessionFactory() - .getCurrentSession().getTransaction().rollback(); - throw new ServletException(ex); - } - -}]]></programlisting> - - <para> - The pattern we are applying here is called <emphasis>session-per-request</emphasis>. - When a request hits the servlet, a new Hibernate <literal>Session</literal> is - opened through the first call to <literal>getCurrentSession()</literal> on the - <literal>SessionFactory</literal>. Then a database transaction is started&mdash;all - data access as to occur inside a transaction, no matter if data is read or written - (we don't use the auto-commit mode in applications). - </para> - - <para> - Do <emphasis>not</emphasis> use a new Hibernate <literal>Session</literal> for - every database operation. Use one Hibernate <literal>Session</literal> that is - scoped to the whole request. Use <literal>getCurrentSession()</literal>, so that - it is automatically bound to the current Java thread. - </para> - - <para> - Next, the possible actions of the request are processed and the response HTML - is rendered. We'll get to that part soon. - </para> - - <para> - Finally, the unit of work ends when processing and rendering is complete. If any - problem occurred during processing or rendering, an exception will be thrown - and the database transaction rolled back. This completes the - <literal>session-per-request</literal> pattern. Instead of the transaction - demarcation code in every servlet you could also write a servlet filter. - See the Hibernate website and Wiki for more information about this pattern, - called <emphasis>Open Session in View</emphasis>&mdash;you'll need it as soon - as you consider rendering your view in JSP, not in a servlet. - </para> - - </sect2> - - <sect2 id="tutorial-webapp-processing" revision="1"> - <title>Processing and rendering</title> - - <para> - Let's implement the processing of the request and rendering of the page. - </para> - -<programlisting><![CDATA[// Write HTML header -PrintWriter out = response.getWriter(); -out.println("<html><head><title>Event Manager</title></head><body>"); - -// Handle actions -if ( "store".equals(request.getParameter("action")) ) { - - String eventTitle = request.getParameter("eventTitle"); - String eventDate = request.getParameter("eventDate"); - - if ( "".equals(eventTitle) || "".equals(eventDate) ) { - out.println("<b><i>Please enter event title and date.</i></b>"); - } else { - createAndStoreEvent(eventTitle, dateFormatter.parse(eventDate)); - out.println("<b><i>Added event.</i></b>"); - } -} - -// Print page -printEventForm(out); -listEvents(out, dateFormatter); - -// Write HTML footer -out.println("</body></html>"); -out.flush(); -out.close();]]></programlisting> - - <para> - Granted, this coding style with a mix of Java and HTML would not scale - in a more complex application&mdash;keep in mind that we are only illustrating - basic Hibernate concepts in this tutorial. The code prints an HTML - header and a footer. Inside this page, an HTML form for event entry and - a list of all events in the database are printed. The first method is - trivial and only outputs HTML: - </para> - - <programlisting><![CDATA[private void printEventForm(PrintWriter out) { - out.println("<h2>Add new event:</h2>"); - out.println("<form>"); - out.println("Title: <input name='eventTitle' length='50'/><br/>"); - out.println("Date (e.g. 24.12.2009): <input name='eventDate' length='10'/><br/>"); - out.println("<input type='submit' name='action' value='store'/>"); - out.println("</form>"); -}]]></programlisting> - - <para> - The <literal>listEvents()</literal> method uses the Hibernate - <literal>Session</literal> bound to the current thread to execute - a query: - </para> - - <programlisting><![CDATA[private void listEvents(PrintWriter out, SimpleDateFormat dateFormatter) { - - List result = HibernateUtil.getSessionFactory() - .getCurrentSession().createCriteria(Event.class).list(); - if (result.size() > 0) { - out.println("<h2>Events in database:</h2>"); - out.println("<table border='1'>"); - out.println("<tr>"); - out.println("<th>Event title</th>"); - out.println("<th>Event date</th>"); - out.println("</tr>"); - for (Iterator it = result.iterator(); it.hasNext();) { - Event event = (Event) it.next(); - out.println("<tr>"); - out.println("<td>" + event.getTitle() + "</td>"); - out.println("<td>" + dateFormatter.format(event.getDate()) + "</td>"); - out.println("</tr>"); - } - out.println("</table>"); - } -}]]></programlisting> - - <para> - Finally, the <literal>store</literal> action is dispatched to the - <literal>createAndStoreEvent()</literal> method, which also uses - the <literal>Session</literal> of the current thread: - </para> - - <programlisting><![CDATA[protected void createAndStoreEvent(String title, Date theDate) { - Event theEvent = new Event(); - theEvent.setTitle(title); - theEvent.setDate(theDate); - - HibernateUtil.getSessionFactory() - .getCurrentSession().save(theEvent); -}]]></programlisting> - - <para> - That's it, the servlet is complete. A request to the servlet will be processed - in a single <literal>Session</literal> and <literal>Transaction</literal>. As - earlier in the standalone application, Hibernate can automatically bind these - objects to the current thread of execution. This gives you the freedom to layer - your code and access the <literal>SessionFactory</literal> in any way you like. - Usually you'd use a more sophisticated design and move the data access code - into data access objects (the DAO pattern). See the Hibernate Wiki for more - examples. - </para> - - </sect2> - - <sect2 id="tutorial-webapp-deploy"> - <title>Deploying and testing</title> - - <para> - To deploy this application you have to create a web archive, a WAR. Add the - following Ant target to your <literal>build.xml</literal>: - </para> - -<programlisting><![CDATA[<target name="war" depends="compile"> - <war destfile="hibernate-tutorial.war" webxml="web.xml"> - <lib dir="${librarydir}"> - <exclude name="jsdk*.jar"/> - </lib> - - <classes dir="${targetdir}"/> - </war> -</target>]]></programlisting> - - <para> - This target creates a file called <literal>hibernate-tutorial.war</literal> - in your project directory. It packages all libraries and the <literal>web.xml</literal> - descriptor, which is expected in the base directory of your project: - </para> - - <programlisting><![CDATA[<?xml version="1.0" encoding="UTF-8"?> -<web-app version="2.4" - xmlns="http://java.sun.com/xml/ns/j2ee" - xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" - xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd"> - - <servlet> - <servlet-name>Event Manager</servlet-name> - <servlet-class>events.EventManagerServlet</servlet-class> - </servlet> - - <servlet-mapping> - <servlet-name>Event Manager</servlet-name> - <url-pattern>/eventmanager</url-pattern> - </servlet-mapping> -</web-app>]]></programlisting> - - <para> - Before you compile and deploy the web application, note that an additional library - is required: <literal>jsdk.jar</literal>. This is the Java servlet development kit, - if you don't have this library already, get it from the Sun website and copy it to - your library directory. However, it will be only used for compilation and excluded - from the WAR package. - </para> - - <para> - To build and deploy call <literal>ant war</literal> in your project directory - and copy the <literal>hibernate-tutorial.war</literal> file into your Tomcat - <literal>webapp</literal> directory. If you don't have Tomcat installed, download - it and follow the installation instructions. You don't have to change any Tomcat - configuration to deploy this application though. - </para> - - <para> - Once deployed and Tomcat is running, access the application at - <literal>http://localhost:8080/hibernate-tutorial/eventmanager</literal>. Make - sure you watch the Tomcat log to see Hibernate initialize when the first - request hits your servlet (the static initializer in <literal>HibernateUtil</literal> - is called) and to get the detailed output if any exceptions occurs. - </para> - - </sect2> - - </sect1> - - <sect1 id="tutorial-summary" revision="1"> - <title>Summary</title> - - <para> - This tutorial covered the basics of writing a simple standalone Hibernate application - and a small web application. - </para> - - <para> - If you already feel confident with Hibernate, continue browsing through the reference - documentation table of contents for topics you find interesting - most asked are - transactional processing (<xref linkend="transactions"/>), fetch - performance (<xref linkend="performance"/>), or the usage of the API (<xref linkend="objectstate"/>) - and the query features (<xref linkend="objectstate-querying"/>). - </para> - - <para> - Don't forget to check the Hibernate website for more (specialized) tutorials. - </para> - - </sect1> - -</chapter> Deleted: core/trunk/documentation/envers/src/main/docbook/en-US/content/xml.xml =================================================================== --- core/trunk/documentation/envers/src/main/docbook/en-US/content/xml.xml 2008-11-04 17:31:01 UTC (rev 15499) +++ core/trunk/documentation/envers/src/main/docbook/en-US/content/xml.xml 2008-11-04 17:31:43 UTC (rev 15500) @@ -1,313 +0,0 @@ -<?xml version='1.0' encoding="UTF-8"?> -<!-- - ~ Hibernate, Relational Persistence for Idiomatic Java - ~ - ~ Copyright (c) 2008, Red Hat Middleware LLC or third-party contributors as - ~ indicated by the @author tags or express copyright attribution - ~ statements applied by the authors. All third-party contributions are - ~ distributed under license by Red Hat Middleware LLC. - ~ - ~ This copyrighted material is made available to anyone wishing to use, modify, - ~ copy, or redistribute it subject to the terms and conditions of the GNU - ~ Lesser General Public License, as published by the Free Software Foundation. - ~ - ~ This program is distributed in the hope that it will be useful, - ~ but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY - ~ or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License - ~ for more details. - ~ - ~ You should have received a copy of the GNU Lesser General Public License - ~ along with this distribution; if not, write to: - ~ Free Software Foundation, Inc. - ~ 51 Franklin Street, Fifth Floor - ~ Boston, MA 02110-1301 USA - --> - -<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd"> - -<chapter id="xml"> - <title>XML Mapping</title> - - <para><emphasis> - Note that this is an experimental feature in Hibernate 3.0 and is under - extremely active development. - </emphasis></para> - - <sect1 id="xml-intro" revision="1"> - <title>Working with XML data</title> - - <para> - Hibernate lets you work with persistent XML data in much the same way - you work with persistent POJOs. A parsed XML tree can be thought of - as just another way to represent the relational data at the object level, - instead of POJOs. - </para> - - <para> - Hibernate supports dom4j as API for manipulating XML trees. You can write - queries that retrieve dom4j trees from the database and have any - modification you make to the tree automatically synchronized to the - database. You can even take an XML document, parse it using dom4j, and - write it to the database with any of Hibernate's basic operations: - <literal>persist(), saveOrUpdate(), merge(), delete(), replicate()</literal> - (merging is not yet supported). - </para> - - <para> - This feature has many applications including data import/export, - externalization of entity data via JMS or SOAP and XSLT-based reporting. - </para> - - <para> - A single mapping may be used to simultaneously map properties of a class - and nodes of an XML document to the database, or, if there is no class to map, - it may be used to map just the XML. - </para> - - <sect2 id="xml-intro-mapping"> - <title>Specifying XML and class mapping together</title> - - <para> - Here is an example of mapping a POJO and XML simultaneously: - </para> - - <programlisting><![CDATA[<class name="Account" - table="ACCOUNTS" - node="account"> - - <id name="accountId" - column="ACCOUNT_ID" - node="@id"/> - - <many-to-one name="customer" - column="CUSTOMER_ID" - node="customer/@id" - embed-xml="false"/> - - <property name="balance" - column="BALANCE" - node="balance"/> - - ... - -</class>]]></programlisting> - </sect2> - - <sect2 id="xml-onlyxml"> - <title>Specifying only an XML mapping</title> - - <para> - Here is an example where there is no POJO class: - </para> - - <programlisting><![CDATA[<class entity-name="Account" - table="ACCOUNTS" - node="account"> - - <id name="id" - column="ACCOUNT_ID" - node="@id" - type="string"/> - - <many-to-one name="customerId" - column="CUSTOMER_ID" - node="customer/@id" - embed-xml="false" - entity-name="Customer"/> - - <property name="balance" - column="BALANCE" - node="balance" - type="big_decimal"/> - - ... - -</class>]]></programlisting> - - <para> - This mapping allows you to access the data as a dom4j tree, or as a graph of - property name/value pairs (java <literal>Map</literal>s). The property names - are purely logical constructs that may be referred to in HQL queries. - </para> - - </sect2> - - </sect1> - - <sect1 id="xml-mapping" revision="1"> - <title>XML mapping metadata</title> - - <para> - Many Hibernate mapping elements accept the <literal>node</literal> attribute. - This let's you specify the name of an XML attribute or element that holds the - property or entity data. The format of the <literal>node</literal> attribute - must be one of the following: - </para> - - <itemizedlist spacing="compact"> - <listitem> - <para><literal>"element-name"</literal> - map to the named XML element</para> - </listitem> - <listitem> - <para><literal>"@attribute-name"</literal> - map to the named XML attribute</para> - </listitem> - <listitem> - <para><literal>"."</literal> - map to the parent element</para> - </listitem> - <listitem> - <para> - <literal>"element-name/@attribute-name"</literal> - - map to the named attribute of the named element - </para> - </listitem> - </itemizedlist> - - <para> - For collections and single valued associations, there is an additional - <literal>embed-xml</literal> attribute. If <literal>embed-xml="true"</literal>, - the default, the XML tree for the associated entity (or collection of value type) - will be embedded directly in the XML tree for the entity that owns the association. - Otherwise, if <literal>embed-xml="false"</literal>, then only the referenced - identifier value will appear in the XML for single point associations and - collections will simply not appear at all. - </para> - - <para> - You should be careful not to leave <literal>embed-xml="true"</literal> for - too many associations, since XML does not deal well with circularity! - </para> - - <programlisting><![CDATA[<class name="Customer" - table="CUSTOMER" - node="customer"> - - <id name="id" - column="CUST_ID" - node="@id"/> - - <map name="accounts" - node="." - embed-xml="true"> - <key column="CUSTOMER_ID" - not-null="true"/> - <map-key column="SHORT_DESC" - node="@short-desc" - type="string"/> - <one-to-many entity-name="Account" - embed-xml="false" - node="account"/> - </map> - - <component name="name" - node="name"> - <property name="firstName" - node="first-name"/> - <property name="initial" - node="initial"/> - <property name="lastName" - node="last-name"/> - </component> - - ... - -</class>]]></programlisting> - - <para> - in this case, we have decided to embed the collection of account ids, but not - the actual account data. The following HQL query: - </para> - - <programlisting><![CDATA[from Customer c left join fetch c.accounts where c.lastName like :lastName]]></programlisting> - - <para> - Would return datasets such as this: - </para> - - <programlisting><![CDATA[<customer id="123456789"> - <account short-desc="Savings">987632567</account> - <account short-desc="Credit Card">985612323</account> - <name> - <first-name>Gavin</first-name> - <initial>A</initial> - <last-name>King</last-name> - </name> - ... -</customer>]]></programlisting> - - <para> - If you set <literal>embed-xml="true"</literal> on the <literal>&lt;one-to-many&gt;</literal> - mapping, the data might look more like this: - </para> - - <programlisting><![CDATA[<customer id="123456789"> - <account id="987632567" short-desc="Savings"> - <customer id="123456789"/> - <balance>100.29</balance> - </account> - <account id="985612323" short-desc="Credit Card"> - <customer id="123456789"/> - <balance>-2370.34</balance> - </account> - <name> - <first-name>Gavin</first-name> - <initial>A</initial> - <last-name>King</last-name> - </name> - ... -</customer>]]></programlisting> - - </sect1> - - - <sect1 id="xml-manipulation" revision="1"> - <title>Manipulating XML data</title> - - <para> - Let's rearead and update XML documents in the application. We do this by - obtaining a dom4j session: - </para> - - <programlisting><![CDATA[Document doc = ....; - -Session session = factory.openSession(); -Session dom4jSession = session.getSession(EntityMode.DOM4J); -Transaction tx = session.beginTransaction(); - -List results = dom4jSession - .createQuery("from Customer c left join fetch c.accounts where c.lastName like :lastName") - .list(); -for ( int i=0; i<results.size(); i++ ) { - //add the customer data to the XML document - Element customer = (Element) results.get(i); - doc.add(customer); -} - -tx.commit(); -session.close();]]></programlisting> - - <programlisting><![CDATA[Session session = factory.openSession(); -Session dom4jSession = session.getSession(EntityMode.DOM4J); -Transaction tx = session.beginTransaction(); - -Element cust = (Element) dom4jSession.get("Customer", customerId); -for ( int i=0; i<results.size(); i++ ) { - Element customer = (Element) results.get(i); - //change the customer name in the XML and database - Element name = customer.element("name"); - name.element("first-name").setText(firstName); - name.element("initial").setText(initial); - name.element("last-name").setText(lastName); -} - -tx.commit(); -session.close();]]></programlisting> - - <para> - It is extremely useful to combine this feature with Hibernate's <literal>replicate()</literal> - operation to implement XML-based data import/export. - </para> - - </sect1> - -</chapter> - Deleted: core/trunk/documentation/envers/src/main/docbook/en-US/images/AuthorWork.png =================================================================== (Binary files differ) Deleted: core/trunk/documentation/envers/src/main/docbook/en-US/images/AuthorWork.zargo =================================================================== (Binary files differ) Deleted: core/trunk/documentation/envers/src/main/docbook/en-US/images/CustomerOrderProduct.png =================================================================== (Binary files differ) Deleted: core/trunk/documentation/envers/src/main/docbook/en-US/images/CustomerOrderProduct.zargo =================================================================== (Binary files differ) Deleted: core/trunk/documentation/envers/src/main/docbook/en-US/images/EmployerEmployee.png =================================================================== (Binary files differ) Deleted: core/trunk/documentation/envers/src/main/docbook/en-US/images/EmployerEmployee.zargo =================================================================== (Binary files differ) Deleted: core/trunk/documentation/envers/src/main/docbook/en-US/images/full_cream.png =================================================================== (Binary files differ) Deleted: core/trunk/documentation/envers/src/main/docbook/en-US/images/full_cream.svg =================================================================== --- core/trunk/documentation/envers/src/main/docbook/en-US/images/full_cream.svg 2008-11-04 17:31:01 UTC (rev 15499) +++ core/trunk/documentation/envers/src/main/docbook/en-US/images/full_cream.svg 2008-11-04 17:31:43 UTC (rev 15500) @@ -1,429 +0,0 @@ -<?xml version="1.0" standalone="no"?> -<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 20010904//EN" -"http://www.w3.org/TR/2001/REC-SVG-20010904/DTD/svg10.dtd" -[ - 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