Author: steve.ebersole(a)jboss.com Date: 2007-10-09 14:14:35 -0400 (Tue, 09 Oct 2007) New Revision: 14073 Added: core/trunk/documentation/manual/en-US/src/main/docbook/Hibernate_Reference.xml core/trunk/documentation/manual/en-US/src/main/docbook/author_group.xml core/trunk/documentation/manual/en-US/src/main/docbook/content/ core/trunk/documentation/manual/en-US/src/main/docbook/content/architecture.xml core/trunk/documentation/manual/en-US/src/main/docbook/content/association_mapping.xml core/trunk/documentation/manual/en-US/src/main/docbook/content/basic_mapping.xml core/trunk/documentation/manual/en-US/src/main/docbook/content/batch.xml core/trunk/documentation/manual/en-US/src/main/docbook/content/best_practices.xml core/trunk/documentation/manual/en-US/src/main/docbook/content/collection_mapping.xml core/trunk/documentation/manual/en-US/src/main/docbook/content/component_mapping.xml core/trunk/documentation/manual/en-US/src/main/docbook/content/configuration.xml core/trunk/documentation/manual/en-US/src/main/docbook/content/events.xml core/trunk/documentation/manual/en-US/src/main/docbook/content/example_mappings.xml core/trunk/documentation/manual/en-US/src/main/docbook/content/example_parentchild.xml core/trunk/documentation/manual/en-US/src/main/docbook/content/example_weblog.xml core/trunk/documentation/manual/en-US/src/main/docbook/content/filters.xml core/trunk/documentation/manual/en-US/src/main/docbook/content/inheritance_mapping.xml core/trunk/documentation/manual/en-US/src/main/docbook/content/performance.xml core/trunk/documentation/manual/en-US/src/main/docbook/content/persistent_classes.xml core/trunk/documentation/manual/en-US/src/main/docbook/content/preface.xml core/trunk/documentation/manual/en-US/src/main/docbook/content/query_criteria.xml core/trunk/documentation/manual/en-US/src/main/docbook/content/query_hql.xml core/trunk/documentation/manual/en-US/src/main/docbook/content/query_sql.xml core/trunk/documentation/manual/en-US/src/main/docbook/content/session_api.xml core/trunk/documentation/manual/en-US/src/main/docbook/content/toolset_guide.xml core/trunk/documentation/manual/en-US/src/main/docbook/content/transactions.xml core/trunk/documentation/manual/en-US/src/main/docbook/content/tutorial.xml core/trunk/documentation/manual/en-US/src/main/docbook/content/xml.xml core/trunk/documentation/manual/en-US/src/main/docbook/legal_notice.xml Removed: core/trunk/documentation/manual/en-US/src/main/docbook/master.xml core/trunk/documentation/manual/en-US/src/main/docbook/modules/ Log: new docbook layout Added: core/trunk/documentation/manual/en-US/src/main/docbook/Hibernate_Reference.xml =================================================================== --- core/trunk/documentation/manual/en-US/src/main/docbook/Hibernate_Reference.xml (rev 0) +++ core/trunk/documentation/manual/en-US/src/main/docbook/Hibernate_Reference.xml 2007-10-09 18:14:35 UTC (rev 14073) @@ -0,0 +1,90 @@ +<?xml version='1.0' encoding="iso-8859-1"?> +<!-- + ~ Copyright (c) 2007, Red Hat Middleware, LLC. All rights reserved. + ~ + ~ 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, v. 2.1. This program is distributed in the + ~ hope that it will be useful, but WITHOUT A 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, v.2.1 along with this + ~ distribution; if not, write to the Free Software Foundation, Inc., + ~ 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. + ~ + ~ Red Hat Author(s): Steve Ebersole + --> +<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [ + <!ENTITY versionNumber "3.3.0.alpha1"> + <!ENTITY copyrightYear "2004"> + <!ENTITY copyrightHolder "Red Hat Middleware, LLC."> +]> + +<book> + + <bookinfo> + <title>HIBERNATE - Relational Persistence for Idiomatic Java</title> + <subtitle>Hibernate Reference Documentation</subtitle> + <releaseinfo>&versionNumber;</releaseinfo> + <productnumber>&versionNumber;</productnumber> + <issuenum>1</issuenum> + <mediaobject> + <imageobject role="fo"> + <imagedata fileref="images/hibernate_logo_a.png" align="center" /> + </imageobject> + <imageobject role="html"> + <imagedata fileref="images/hibernate_logo_a.png" depth="3cm" /> + </imageobject> + </mediaobject> + <copyright> + <year>&copyrightYear;</year> + <holder>&copyrightHolder;</holder> + </copyright> + <!-- + todo : figure out how best to include translator info... + <xi:include href="author_group.xml" xmlns:xi="http://www.w3.org/2001/XInclude" /> + --> + <xi:include href="legal_notice.xml" xmlns:xi="http://www.w3.org/2001/XInclude" /> + </bookinfo> + + <toc/> + + <xi:include href="content/preface.xml" xmlns:xi="http://www.w3.org/2001/XInclude" /> + + <xi:include href="content/tutorial.xml" xmlns:xi="http://www.w3.org/2001/XInclude" /> + + <xi:include href="content/architecture.xml" xmlns:xi="http://www.w3.org/2001/XInclude" /> + + <xi:include href="content/configuration.xml" xmlns:xi="http://www.w3.org/2001/XInclude" /> + + <xi:include href="content/persistent_classes.xml" xmlns:xi="http://www.w3.org/2001/XInclude" /> + + <xi:include href="content/basic_mapping.xml" xmlns:xi="http://www.w3.org/2001/XInclude" /> + <xi:include href="content/collection_mapping.xml" xmlns:xi="http://www.w3.org/2001/XInclude" /> + <xi:include href="content/association_mapping.xml" xmlns:xi="http://www.w3.org/2001/XInclude" /> + <xi:include href="content/component_mapping.xml" xmlns:xi="http://www.w3.org/2001/XInclude" /> + <xi:include href="content/inheritance_mapping.xml" xmlns:xi="http://www.w3.org/2001/XInclude" /> + + <xi:include href="content/session_api.xml" xmlns:xi="http://www.w3.org/2001/XInclude" /> + <xi:include href="content/transactions.xml" xmlns:xi="http://www.w3.org/2001/XInclude" /> + <xi:include href="content/events.xml" xmlns:xi="http://www.w3.org/2001/XInclude" /> + <xi:include href="content/batch.xml" xmlns:xi="http://www.w3.org/2001/XInclude" /> + + <xi:include href="content/query_hql.xml" xmlns:xi="http://www.w3.org/2001/XInclude" /> + <xi:include href="content/query_criteria.xml" xmlns:xi="http://www.w3.org/2001/XInclude" /> + <xi:include href="content/query_sql.xml" xmlns:xi="http://www.w3.org/2001/XInclude" /> + <xi:include href="content/filters.xml" xmlns:xi="http://www.w3.org/2001/XInclude" /> + <xi:include href="content/xml.xml" xmlns:xi="http://www.w3.org/2001/XInclude" /> + + <xi:include href="content/performance.xml" xmlns:xi="http://www.w3.org/2001/XInclude" /> + + <xi:include href="content/toolset_guide.xml" xmlns:xi="http://www.w3.org/2001/XInclude" /> + + <xi:include href="content/example_parentchild.xml" xmlns:xi="http://www.w3.org/2001/XInclude" /> + <xi:include href="content/example_weblog.xml" xmlns:xi="http://www.w3.org/2001/XInclude" /> + <xi:include href="content/example_mappings.xml" xmlns:xi="http://www.w3.org/2001/XInclude" /> + + <xi:include href="content/best_practices.xml" xmlns:xi="http://www.w3.org/2001/XInclude" /> + +</book> + Added: core/trunk/documentation/manual/en-US/src/main/docbook/author_group.xml =================================================================== --- core/trunk/documentation/manual/en-US/src/main/docbook/author_group.xml (rev 0) +++ core/trunk/documentation/manual/en-US/src/main/docbook/author_group.xml 2007-10-09 18:14:35 UTC (rev 14073) @@ -0,0 +1,30 @@ +<?xml version='1.0'?> +<!-- + ~ Copyright (c) 2007, Red Hat Middleware, LLC. All rights reserved. + ~ + ~ 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, v. 2.1. This program is distributed in the + ~ hope that it will be useful, but WITHOUT A 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, v.2.1 along with this + ~ distribution; if not, write to the Free Software Foundation, Inc., + ~ 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. + ~ + ~ Red Hat Author(s): Steve Ebersole + --> +<!DOCTYPE authorgroup PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd"> + +<authorgroup id="AuthorGroup"> + <collab> + <collabname>The Hibernate team</collabname> + </collab> + <!-- translations should list all contributors to the translation using the 'translator' class + <othercredit class="translator"> + <firstname>Jane</firstname> + <surname>Doe</surname> + <contrib>Japenese translation</contrib> + </othercredit> + --> +</authorgroup> \ No newline at end of file Copied: core/trunk/documentation/manual/en-US/src/main/docbook/content/architecture.xml (from rev 12794, core/trunk/documentation/manual/en-US/src/main/docbook/modules/architecture.xml) =================================================================== --- core/trunk/documentation/manual/en-US/src/main/docbook/content/architecture.xml (rev 0) +++ core/trunk/documentation/manual/en-US/src/main/docbook/content/architecture.xml 2007-10-09 18:14:35 UTC (rev 14073) @@ -0,0 +1,373 @@ +<?xml version='1.0' encoding="iso-8859-1"?> +<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd"> + +<!-- + ~ Copyright (c) 2007, Red Hat Middleware, LLC. All rights reserved. + ~ + ~ 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, v. 2.1. This program is distributed in the + ~ hope that it will be useful, but WITHOUT A 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, v.2.1 along with this + ~ distribution; if not, write to the Free Software Foundation, Inc., + ~ 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. + ~ + ~ Red Hat Author(s): Steve Ebersole + --> +<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 corrsponding 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 programatic transaction demarcation in plain JSE without JTA, you are adviced 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> + Copied: core/trunk/documentation/manual/en-US/src/main/docbook/content/association_mapping.xml (from rev 12794, core/trunk/documentation/manual/en-US/src/main/docbook/modules/association_mapping.xml) =================================================================== --- core/trunk/documentation/manual/en-US/src/main/docbook/content/association_mapping.xml (rev 0) +++ core/trunk/documentation/manual/en-US/src/main/docbook/content/association_mapping.xml 2007-10-09 18:14:35 UTC (rev 14073) @@ -0,0 +1,626 @@ +<?xml version='1.0' encoding="iso-8859-1"?> +<!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> + Copied: core/trunk/documentation/manual/en-US/src/main/docbook/content/basic_mapping.xml (from rev 12794, core/trunk/documentation/manual/en-US/src/main/docbook/modules/basic_mapping.xml) =================================================================== --- core/trunk/documentation/manual/en-US/src/main/docbook/content/basic_mapping.xml (rev 0) +++ core/trunk/documentation/manual/en-US/src/main/docbook/content/basic_mapping.xml 2007-10-09 18:14:35 UTC (rev 14073) @@ -0,0 +1,3565 @@ +<?xml version='1.0' encoding="iso-8859-1"?> +<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [ + <!ENTITY mdash "-"> +]> + +<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 <xref linkend="mapping-types-custom">typedef</xref>. + </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 <xref linkend="mapping-generated">generated properties</xref>. + </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 <xref linkend="mapping-generated">generated properties</xref>. + </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 <xref linkend="mapping-generated">generated properties</xref>. + </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> + </calloutlist> + <callout arearefs="manytoone16"> + <para> + <literal>formula</literal> (optional): an SQL expression that defines the value for a + <emphasis>computed</emphasis> foreign key. + </para> + </callout> + </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 <xref linkend="mapping-declaration-version">versions</xref>, + <xref linkend="mapping-declaration-timestamp">timestamps</xref>, and + <xref linkend="mapping-declaration-property">simple properties</xref> 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 + <xref linkend="mapping-declaration-version">version</xref> and + <xref linkend="mapping-declaration-timestamp">timestamp</xref> 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> + Copied: core/trunk/documentation/manual/en-US/src/main/docbook/content/batch.xml (from rev 12794, core/trunk/documentation/manual/en-US/src/main/docbook/modules/batch.xml) =================================================================== --- core/trunk/documentation/manual/en-US/src/main/docbook/content/batch.xml (rev 0) +++ core/trunk/documentation/manual/en-US/src/main/docbook/content/batch.xml 2007-10-09 18:14:35 UTC (rev 14073) @@ -0,0 +1,350 @@ +<?xml version='1.0' encoding="iso-8859-1"?> +<!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 (<xref linkend="queryhql">HQL</xref>). + </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 <xref linkend="queryhql-joins-forms">joins</xref> (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 + <xref linkend="mapping-declaration-version">version</xref> + or the <xref linkend="mapping-declaration-timestamp">timestamp</xref> 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> Copied: core/trunk/documentation/manual/en-US/src/main/docbook/content/best_practices.xml (from rev 12794, core/trunk/documentation/manual/en-US/src/main/docbook/modules/best_practices.xml) =================================================================== --- core/trunk/documentation/manual/en-US/src/main/docbook/content/best_practices.xml (rev 0) +++ core/trunk/documentation/manual/en-US/src/main/docbook/content/best_practices.xml 2007-10-09 18:14:35 UTC (rev 14073) @@ -0,0 +1,226 @@ +<?xml version='1.0' encoding="iso-8859-1"?> +<!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> + Copied: core/trunk/documentation/manual/en-US/src/main/docbook/content/collection_mapping.xml (from rev 12794, core/trunk/documentation/manual/en-US/src/main/docbook/modules/collection_mapping.xml) =================================================================== --- core/trunk/documentation/manual/en-US/src/main/docbook/content/collection_mapping.xml (rev 0) +++ core/trunk/documentation/manual/en-US/src/main/docbook/content/collection_mapping.xml 2007-10-09 18:14:35 UTC (rev 14073) @@ -0,0 +1,1234 @@ +<?xml version='1.0' encoding="iso-8859-1"?> +<!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> + + <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> + + <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> + + <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> Copied: core/trunk/documentation/manual/en-US/src/main/docbook/content/component_mapping.xml (from rev 12794, core/trunk/documentation/manual/en-US/src/main/docbook/modules/component_mapping.xml) =================================================================== --- core/trunk/documentation/manual/en-US/src/main/docbook/content/component_mapping.xml (rev 0) +++ core/trunk/documentation/manual/en-US/src/main/docbook/content/component_mapping.xml 2007-10-09 18:14:35 UTC (rev 14073) @@ -0,0 +1,405 @@ +<?xml version='1.0' encoding="iso-8859-1"?> +<!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> Copied: core/trunk/documentation/manual/en-US/src/main/docbook/content/configuration.xml (from rev 12794, core/trunk/documentation/manual/en-US/src/main/docbook/modules/configuration.xml) =================================================================== --- core/trunk/documentation/manual/en-US/src/main/docbook/content/configuration.xml (rev 0) +++ core/trunk/documentation/manual/en-US/src/main/docbook/content/configuration.xml 2007-10-09 18:14:35 UTC (rev 14073) @@ -0,0 +1,1746 @@ +<?xml version='1.0' encoding="iso-8859-1"?> +<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [ + <!ENTITY mdash "-"> +]> + +<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 <literal>org.hibernate.cfg.Configuration</literal> + represents an entire set of mappings of an application's Java types to an + SQL database. The <literal>Configuration</literal> is used to build an + (immutable) <literal>SessionFactory</literal>. The mappings are compiled + from various XML mapping files. + </para> + + <para> + You may obtain a <literal>Configuration</literal> 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 + <literal>/org/hibernate/auction/Item.hbm.xml</literal> and + <literal>/org/hibernate/auction/Bid.hbm.xml</literal> in the classpath. + This approach eliminates any hardcoded filenames. + </para> + + <para> + A <literal>Configuration</literal> 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 <literal>java.util.Properties</literal> to + <literal>Configuration.setProperties()</literal>. + </para> + </listitem> + <listitem> + <para> + Place <literal>hibernate.properties</literal> 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> + <literal>hibernate.properties</literal> is the easiest approach if you + want to get started quickly. + </para> + + <para> + The <literal>Configuration</literal> 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 <literal>Configuration</literal>, + the application must obtain a factory for <literal>Session</literal> 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 + <literal>SessionFactory</literal>. 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 <literal>SessionFactory</literal> create and pool JDBC + connections for you. If you take this approach, opening a <literal>Session</literal> + 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 + <literal>org.hibernate.cfg.Environment</literal>. We will now describe the most + important settings for JDBC connection configuration. + </para> + + <para> + Hibernate will obtain (and pool) connections using <literal>java.sql.DriverManager</literal> + 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> + <literal>hibernate.connection.driver_class</literal> + </entry> + <entry> + <emphasis>JDBC driver class</emphasis> + </entry> + </row> + <row> + <entry> + <literal>hibernate.connection.url</literal> + </entry> + <entry> + <emphasis>JDBC URL</emphasis> + </entry> + </row> + <row> + <entry> + <literal>hibernate.connection.username</literal> + </entry> + <entry> + <emphasis>database user</emphasis> + </entry> + </row> + <row> + <entry> + <literal>hibernate.connection.password</literal> + </entry> + <entry> + <emphasis>database user password</emphasis> + </entry> + </row> + <row> + <entry> + <literal>hibernate.connection.pool_size</literal> + </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 + <literal>hibernate.connection.pool_size</literal> 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 <literal>lib</literal> directory. Hibernate will use its + <literal>C3P0ConnectionProvider</literal> for connection pooling if you set + <literal>hibernate.c3p0.*</literal> properties. If you'd like to use Proxool + refer to the packaged <literal>hibernate.properties</literal> and the Hibernate + web site for more information. + </para> + + <para> + Here is an example <literal>hibernate.properties</literal> 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 + <literal>Datasource</literal> 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> + <literal>hibernate.connection.datasource</literal> + </entry> + <entry> + <emphasis>datasource JNDI name</emphasis> + </entry> + </row> + <row> + <entry> + <literal>hibernate.jndi.url</literal> + </entry> + <entry> + <emphasis>URL of the JNDI provider</emphasis> (optional) + </entry> + </row> + <row> + <entry> + <literal>hibernate.jndi.class</literal> + </entry> + <entry> + <emphasis>class of the JNDI <literal>InitialContextFactory</literal></emphasis> (optional) + </entry> + </row> + <row> + <entry> + <literal>hibernate.connection.username</literal> + </entry> + <entry> + <emphasis>database user</emphasis> (optional) + </entry> + </row> + <row> + <entry> + <literal>hibernate.connection.password</literal> + </entry> + <entry> + <emphasis>database user password</emphasis> (optional) + </entry> + </row> + </tbody> + </tgroup> + </table> + + <para> + Here's an example <literal>hibernate.properties</literal> 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 property name. For example, you + may specify a <literal>charSet</literal> using <literal>hibernate.connection.charSet</literal>. + </para> + + <para> + You may define your own plugin strategy for obtaining JDBC connections by implementing the + interface <literal>org.hibernate.connection.ConnectionProvider</literal>. You may select + a custom implementation by setting <literal>hibernate.connection.provider_class</literal>. + </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 + <literal>hibernate.properties</literal>. 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> + <literal>hibernate.dialect</literal> + </entry> + <entry> + The classname of a Hibernate <literal>Dialect</literal> 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> + </entry> + </row> + <row> + <entry> + <literal>hibernate.show_sql</literal> + </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> + <literal>hibernate.format_sql</literal> + </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> + <literal>hibernate.default_schema</literal> + </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> + <literal>hibernate.default_catalog</literal> + </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> + <literal>hibernate.session_factory_name</literal> + </entry> + <entry> + The <literal>SessionFactory</literal> 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> + <literal>hibernate.max_fetch_depth</literal> + </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> + <literal>hibernate.default_batch_fetch_size</literal> + </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> + <literal>hibernate.default_entity_mode</literal> + </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> + <literal>hibernate.order_updates</literal> + </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> + <literal>hibernate.generate_statistics</literal> + </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> + <literal>hibernate.use_identifier_rollback</literal> + </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> + <literal>hibernate.use_sql_comments</literal> + </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> + <literal>hibernate.jdbc.fetch_size</literal> + </entry> + <entry> + A non-zero value determines the JDBC fetch size (calls + <literal>Statement.setFetchSize()</literal>). + </entry> + </row> + <row> + <entry> + <literal>hibernate.jdbc.batch_size</literal> + </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> + <literal>hibernate.jdbc.batch_versioned_data</literal> + </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> + <literal>hibernate.jdbc.factory_class</literal> + </entry> + <entry> + Select a custom <literal>Batcher</literal>. Most applications + will not need this configuration property. + <para> + <emphasis role="strong">eg.</emphasis> + <literal>classname.of.BatcherFactory</literal> + </para> + </entry> + </row> + <row> + <entry> + <literal>hibernate.jdbc.use_scrollable_resultset</literal> + </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> + <literal>hibernate.jdbc.use_streams_for_binary</literal> + </entry> + <entry> + Use streams when writing/reading <literal>binary</literal> + or <literal>serializable</literal> types to/from JDBC + (system-level property). + <para> + <emphasis role="strong">eg.</emphasis> + <literal>true</literal> | <literal>false</literal> + </para> + </entry> + </row> + <row> + <entry> + <literal>hibernate.jdbc.use_get_generated_keys</literal> + </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> + <literal>hibernate.connection.provider_class</literal> + </entry> + <entry> + The classname of a custom <literal>ConnectionProvider</literal> which provides + JDBC connections to Hibernate. + <para> + <emphasis role="strong">eg.</emphasis> + <literal>classname.of.ConnectionProvider</literal> + </para> + </entry> + </row> + <row> + <entry> + <literal>hibernate.connection.isolation</literal> + </entry> + <entry> + Set the JDBC transaction isolation level. Check + <literal>java.sql.Connection</literal> for meaningful values but + note that most databases do not support all isolation levels. + <para> + <emphasis role="strong">eg.</emphasis> + <literal>1, 2, 4, 8</literal> + </para> + </entry> + </row> + <row> + <entry> + <literal>hibernate.connection.autocommit</literal> + </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> + <literal>hibernate.connection.release_mode</literal> + </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> + <literal>hibernate.connection.<emphasis>&lt;propertyName&gt;</emphasis></literal> + </entry> + <entry> + Pass the JDBC property <literal>propertyName</literal> + to <literal>DriverManager.getConnection()</literal>. + </entry> + </row> + <row> + <entry> + <literal>hibernate.jndi.<emphasis>&lt;propertyName&gt;</emphasis></literal> + </entry> + <entry> + Pass the property <literal>propertyName</literal> 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 logs various events using Apache commons-logging. + </para> + + <para> + The commons-logging service will direct output to either Apache Log4j + (if you include <literal>log4j.jar</literal> in your classpath) or + JDK1.4 logging (if running under JDK1.4 or above). You may download + Log4j from <literal>http://jakarta.apache.org</literal>. + To use Log4j you will need to place a <literal>log4j.properties</literal> + 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 <xref linkend="architecture-current-session">current sessions</xref>. + 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> + Copied: core/trunk/documentation/manual/en-US/src/main/docbook/content/events.xml (from rev 12794, core/trunk/documentation/manual/en-US/src/main/docbook/modules/events.xml) =================================================================== --- core/trunk/documentation/manual/en-US/src/main/docbook/content/events.xml (rev 0) +++ core/trunk/documentation/manual/en-US/src/main/docbook/content/events.xml 2007-10-09 18:14:35 UTC (rev 14073) @@ -0,0 +1,268 @@ +<?xml version='1.0' encoding="iso-8859-1"?> +<!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> + Copied: core/trunk/documentation/manual/en-US/src/main/docbook/content/example_mappings.xml (from rev 12794, core/trunk/documentation/manual/en-US/src/main/docbook/modules/example_mappings.xml) =================================================================== --- core/trunk/documentation/manual/en-US/src/main/docbook/content/example_mappings.xml (rev 0) +++ core/trunk/documentation/manual/en-US/src/main/docbook/content/example_mappings.xml 2007-10-09 18:14:35 UTC (rev 14073) @@ -0,0 +1,676 @@ +<?xml version='1.0' encoding="iso-8859-1"?> +<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd"> + +<!-- + ~ Copyright (c) 2007, Red Hat Middleware, LLC. All rights reserved. + ~ + ~ 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, v. 2.1. This program is distributed in the + ~ hope that it will be useful, but WITHOUT A 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, v.2.1 along with this + ~ distribution; if not, write to the Free Software Foundation, Inc., + ~ 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. + ~ + ~ Red Hat Author(s): Steve Ebersole + --> +<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> + Copied: core/trunk/documentation/manual/en-US/src/main/docbook/content/example_parentchild.xml (from rev 12794, core/trunk/documentation/manual/en-US/src/main/docbook/modules/example_parentchild.xml) =================================================================== --- core/trunk/documentation/manual/en-US/src/main/docbook/content/example_parentchild.xml (rev 0) +++ core/trunk/documentation/manual/en-US/src/main/docbook/content/example_parentchild.xml 2007-10-09 18:14:35 UTC (rev 14073) @@ -0,0 +1,364 @@ +<?xml version='1.0' encoding="iso-8859-1"?> +<!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> \ No newline at end of file Copied: core/trunk/documentation/manual/en-US/src/main/docbook/content/example_weblog.xml (from rev 12794, core/trunk/documentation/manual/en-US/src/main/docbook/modules/example_weblog.xml) =================================================================== --- core/trunk/documentation/manual/en-US/src/main/docbook/content/example_weblog.xml (rev 0) +++ core/trunk/documentation/manual/en-US/src/main/docbook/content/example_weblog.xml 2007-10-09 18:14:35 UTC (rev 14073) @@ -0,0 +1,433 @@ +<?xml version='1.0' encoding="iso-8859-1"?> +<!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> + Copied: core/trunk/documentation/manual/en-US/src/main/docbook/content/filters.xml (from rev 12794, core/trunk/documentation/manual/en-US/src/main/docbook/modules/filters.xml) =================================================================== --- core/trunk/documentation/manual/en-US/src/main/docbook/content/filters.xml (rev 0) +++ core/trunk/documentation/manual/en-US/src/main/docbook/content/filters.xml 2007-10-09 18:14:35 UTC (rev 14073) @@ -0,0 +1,149 @@ +<?xml version='1.0' encoding="iso-8859-1"?> +<!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.enabledFilter()</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.enabledFilter("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> + Copied: core/trunk/documentation/manual/en-US/src/main/docbook/content/inheritance_mapping.xml (from rev 12794, core/trunk/documentation/manual/en-US/src/main/docbook/modules/inheritance_mapping.xml) =================================================================== --- core/trunk/documentation/manual/en-US/src/main/docbook/content/inheritance_mapping.xml (rev 0) +++ core/trunk/documentation/manual/en-US/src/main/docbook/content/inheritance_mapping.xml 2007-10-09 18:14:35 UTC (rev 14073) @@ -0,0 +1,494 @@ +<?xml version='1.0' encoding="iso-8859-1"?> +<!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> Copied: core/trunk/documentation/manual/en-US/src/main/docbook/content/performance.xml (from rev 12794, core/trunk/documentation/manual/en-US/src/main/docbook/modules/performance.xml) =================================================================== --- core/trunk/documentation/manual/en-US/src/main/docbook/content/performance.xml (rev 0) +++ core/trunk/documentation/manual/en-US/src/main/docbook/content/performance.xml 2007-10-09 18:14:35 UTC (rev 14073) @@ -0,0 +1,1391 @@ +<?xml version='1.0' encoding="iso-8859-1"?> +<!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>Sesssion</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 prefered 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 TreeCache</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> + </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 (preferrably?), 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> + + <para> + None of the cache providers support all of the cache concurrency strategies. 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 TreeCache</entry> + <entry>yes</entry> + <entry></entry> + <entry></entry> + <entry>yes</entry> + </row> + </tbody> + </tgroup> + </table> + + </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 efficently. 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 programatically 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 exampl,e 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> \ No newline at end of file Copied: core/trunk/documentation/manual/en-US/src/main/docbook/content/persistent_classes.xml (from rev 12794, core/trunk/documentation/manual/en-US/src/main/docbook/modules/persistent_classes.xml) =================================================================== --- core/trunk/documentation/manual/en-US/src/main/docbook/content/persistent_classes.xml (rev 0) +++ core/trunk/documentation/manual/en-US/src/main/docbook/content/persistent_classes.xml 2007-10-09 18:14:35 UTC (rev 14073) @@ -0,0 +1,534 @@ +<?xml version='1.0' encoding="iso-8859-1"?> +<!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> + + <para> + TODO: Document user-extension framework in the property and proxy packages + </para> + +</chapter> + Added: core/trunk/documentation/manual/en-US/src/main/docbook/content/preface.xml =================================================================== --- core/trunk/documentation/manual/en-US/src/main/docbook/content/preface.xml (rev 0) +++ core/trunk/documentation/manual/en-US/src/main/docbook/content/preface.xml 2007-10-09 18:14:35 UTC (rev 14073) @@ -0,0 +1,123 @@ +<?xml version='1.0'?> +<!-- + ~ Copyright (c) 2007, Red Hat Middleware, LLC. All rights reserved. + ~ + ~ 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, v. 2.1. This program is distributed in the + ~ hope that it will be useful, but WITHOUT A 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, v.2.1 along with this + ~ distribution; if not, write to the Free Software Foundation, Inc., + ~ 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. + ~ + ~ Red Hat Author(s): Steve Ebersole + --> +<!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> \ No newline at end of file Copied: core/trunk/documentation/manual/en-US/src/main/docbook/content/query_criteria.xml (from rev 12794, core/trunk/documentation/manual/en-US/src/main/docbook/modules/query_criteria.xml) =================================================================== --- core/trunk/documentation/manual/en-US/src/main/docbook/content/query_criteria.xml (rev 0) +++ core/trunk/documentation/manual/en-US/src/main/docbook/content/query_criteria.xml 2007-10-09 18:14:35 UTC (rev 14073) @@ -0,0 +1,439 @@ +<?xml version='1.0' encoding="iso-8859-1"?> +<!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> Copied: core/trunk/documentation/manual/en-US/src/main/docbook/content/query_hql.xml (from rev 12794, core/trunk/documentation/manual/en-US/src/main/docbook/modules/query_hql.xml) =================================================================== --- core/trunk/documentation/manual/en-US/src/main/docbook/content/query_hql.xml (rev 0) +++ core/trunk/documentation/manual/en-US/src/main/docbook/content/query_hql.xml 2007-10-09 18:14:35 UTC (rev 14073) @@ -0,0 +1,1237 @@ +<?xml version='1.0' encoding="iso-8859-1"?> +<!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-coomponents"/> 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 from Person p]]></programlisting> + <programlisting><![CDATA[select p.name.first from 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 from Person p where p.name = :name]]></programlisting> + <programlisting><![CDATA[from 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 from Person p order by p.name]]></programlisting> + <programlisting><![CDATA[from from Person p order by p.name.first]]></programlisting> + + <para> + Another common use of components is in <xref linkend="queryhql-tuple">row value constructors</xref>. + </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 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> + Copied: core/trunk/documentation/manual/en-US/src/main/docbook/content/query_sql.xml (from rev 12794, core/trunk/documentation/manual/en-US/src/main/docbook/modules/query_sql.xml) =================================================================== --- core/trunk/documentation/manual/en-US/src/main/docbook/content/query_sql.xml (rev 0) +++ core/trunk/documentation/manual/en-US/src/main/docbook/content/query_sql.xml 2007-10-09 18:14:35 UTC (rev 14073) @@ -0,0 +1,760 @@ +<?xml version='1.0' encoding="iso-8859-1"?> +<!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>ResultSetMetdata</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> + + <p>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.</p> + </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 specificed 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 explicity, 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 accross + 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> \ No newline at end of file Copied: core/trunk/documentation/manual/en-US/src/main/docbook/content/session_api.xml (from rev 12794, core/trunk/documentation/manual/en-US/src/main/docbook/modules/session_api.xml) =================================================================== --- core/trunk/documentation/manual/en-US/src/main/docbook/content/session_api.xml (rev 0) +++ core/trunk/documentation/manual/en-US/src/main/docbook/content/session_api.xml 2007-10-09 18:14:35 UTC (rev 14073) @@ -0,0 +1,1263 @@ +<?xml version='1.0' encoding="iso-8859-1"?> +<!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> + Copied: core/trunk/documentation/manual/en-US/src/main/docbook/content/toolset_guide.xml (from rev 12794, core/trunk/documentation/manual/en-US/src/main/docbook/modules/toolset_guide.xml) =================================================================== --- core/trunk/documentation/manual/en-US/src/main/docbook/content/toolset_guide.xml (rev 0) +++ core/trunk/documentation/manual/en-US/src/main/docbook/content/toolset_guide.xml 2007-10-09 18:14:35 UTC (rev 14073) @@ -0,0 +1,607 @@ +<?xml version='1.0' encoding="iso-8859-1"?> +<!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> + Copied: core/trunk/documentation/manual/en-US/src/main/docbook/content/transactions.xml (from rev 12794, core/trunk/documentation/manual/en-US/src/main/docbook/modules/transactions.xml) =================================================================== --- core/trunk/documentation/manual/en-US/src/main/docbook/content/transactions.xml (rev 0) +++ core/trunk/documentation/manual/en-US/src/main/docbook/content/transactions.xml 2007-10-09 18:14:35 UTC (rev 14073) @@ -0,0 +1,1112 @@ +<?xml version='1.0' encoding="iso-8859-1"?> +<!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 send 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 send 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 converastion. + 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 occured 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 explicitely. + </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> + Datatabase (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 demaracation. 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 <xref linkend="objectstate-flushing">FlushMode</xref> 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 programatically, + 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 + compatiblity), 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> explicity 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 eexception + into a more meningful 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 functioanlity 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 ojects 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 occured. + </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 concepetually 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 uneccessary 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 worring about locking strategies. Its 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 obatins 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> + Copied: core/trunk/documentation/manual/en-US/src/main/docbook/content/tutorial.xml (from rev 12794, core/trunk/documentation/manual/en-US/src/main/docbook/modules/tutorial.xml) =================================================================== --- core/trunk/documentation/manual/en-US/src/main/docbook/content/tutorial.xml (rev 0) +++ core/trunk/documentation/manual/en-US/src/main/docbook/content/tutorial.xml 2007-10-09 18:14:35 UTC (rev 14073) @@ -0,0 +1,1559 @@ +<?xml version='1.0' encoding="iso-8859-1"?> +<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [ + <!ENTITY mdash "-"> +]> + +<chapter id="tutorial"> + <title>Introduction to Hibernate</title> + + <sect1 id="tutorial-intro" revision="1"> + <title>Preface</title> + + <para> + This chapter is an introductory tutorial for new users of Hibernate. We start + with a simple command line application using an in-memory database and develop + it in easy to understand steps. + </para> + + <para> + This tutorial is intended for new users of Hibernate but requires Java and + SQL knowledge. It is based on a tutorial by Michael Gloegl, the third-party + libraries we name are for JDK 1.4 and 5.0. You might need others for JDK 1.3. + </para> + + <para> + The source code for the tutorial is included in the distribution in the + <literal>doc/reference/tutorial/</literal> directory. + </para> + + </sect1> + + <sect1 id="tutorial-firstapp" revision="2"> + <title>Part 1 - The first Hibernate Application</title> + + <para> + First, we'll create a simple console-based Hibernate application. We use an + Java database (HSQL DB), so we do not have to install any database server. + </para> + + <para> + Let's assume we need a small database application that can store events we want to + attend, and information about the hosts of these events. + </para> + + <para> + The first thing we do, is set up our development directory and put all the + Java libraries we need into it. Download the Hibernate distribution from the + Hibernate website. Extract the package and place all required libraries + found in <literal>/lib</literal> into into the <literal>/lib</literal> directory + of your new development working directory. It should look like this: + </para> + + <programlisting><![CDATA[. ++lib + antlr.jar + cglib.jar + asm.jar + asm-attrs.jars + commons-collections.jar + commons-logging.jar + hibernate3.jar + jta.jar + dom4j.jar + log4j.jar ]]></programlisting> + + <para> + This is the minimum set of required libraries (note that we also copied + hibernate3.jar, the main archive) for Hibernate <emphasis>at the time of writing</emphasis>. + The Hibernate release you are using might require more or less libraries. See the + <literal>README.txt</literal> file in the <literal>lib/</literal> directory of the + Hibernate distribution for more information about required and optional third-party + libraries. (Actually, Log4j is not required but preferred by many developers.) + </para> + + <para> + Next we create a class that represents the event we want to store in database. + </para> + + <sect2 id="tutorial-firstapp-firstclass" revision="1"> + <title>The first class</title> + + <para> + Our first persistent class is a simple JavaBean class with some properties: + </para> + + <programlisting><![CDATA[package events; + +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" revision="1"> + <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 identifer 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 continous 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 didnt' 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 defensive 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> + + <para> + Let's turn this into a small web application. + </para> + + </sect1> + + <sect1 id="tutorial-webapp"> + <title>Part 3 - The EventManager web application</title> + + <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 occured 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 + ojects 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 compliation 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> Copied: core/trunk/documentation/manual/en-US/src/main/docbook/content/xml.xml (from rev 12794, core/trunk/documentation/manual/en-US/src/main/docbook/modules/xml.xml) =================================================================== --- core/trunk/documentation/manual/en-US/src/main/docbook/content/xml.xml (rev 0) +++ core/trunk/documentation/manual/en-US/src/main/docbook/content/xml.xml 2007-10-09 18:14:35 UTC (rev 14073) @@ -0,0 +1,289 @@ +<?xml version='1.0' encoding="iso-8859-1"?> +<!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> + Added: core/trunk/documentation/manual/en-US/src/main/docbook/legal_notice.xml =================================================================== --- core/trunk/documentation/manual/en-US/src/main/docbook/legal_notice.xml (rev 0) +++ core/trunk/documentation/manual/en-US/src/main/docbook/legal_notice.xml 2007-10-09 18:14:35 UTC (rev 14073) @@ -0,0 +1,52 @@ +<?xml version='1.0'?> +<!-- + ~ Copyright (c) 2007, Red Hat Middleware, LLC. All rights reserved. + ~ + ~ 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, v. 2.1. This program is distributed in the + ~ hope that it will be useful, but WITHOUT A 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, v.2.1 along with this + ~ distribution; if not, write to the Free Software Foundation, Inc., + ~ 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. + ~ + ~ Red Hat Author(s): Steve Ebersole + --> +<!DOCTYPE legalnotice PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd"> + +<legalnotice id="Legal_Notice"> + <title>Legal Notice</title> + <para> + <address> + <street>1801 Varsity Drive</street> + <city>Raleigh</city>, <state>NC</state><postcode>27606-2072</postcode><country>USA</country> + <phone>Phone: +1 919 754 3700</phone> + <phone>Phone: 888 733 4281</phone> + <fax>Fax: +1 919 754 3701</fax> + <pob>PO Box 13588</pob><city>Research Triangle Park</city>, <state>NC</state><postcode>27709</postcode><country>USA</country> + </address> + </para> + <para> + Copyright <trademark class="copyright"></trademark> 2007 by Red Hat, Inc. This material may be distributed only subject to the terms and conditions set forth in the Open Publication License, V1.0 or later (the latest version is presently available at <ulink url="http://www.opencontent.org/openpub/">http://www.opencon...>). + </para> + <para> + Distribution of substantively modified versions of this document is prohibited without the explicit permission of the copyright holder. + </para> + <para> + Distribution of the work or derivative of the work in any standard (paper) book form for commercial purposes is prohibited unless prior permission is obtained from the copyright holder. + </para> + <para> + Red Hat and the Red Hat "Shadow Man" logo are registered trademarks of Red Hat, Inc. in the United States and other countries. + </para> + <para> + All other trademarks referenced herein are the property of their respective owners. + </para> + <para> + The GPG fingerprint of the security(a)redhat.com key is: + </para> + <para> + CA 20 86 86 2B D6 9D FC 65 F6 EC C4 21 91 80 CD DB 42 A6 0E + </para> +</legalnotice> \ No newline at end of file Deleted: core/trunk/documentation/manual/en-US/src/main/docbook/master.xml =================================================================== --- core/trunk/documentation/manual/en-US/src/main/docbook/master.xml 2007-10-09 17:58:42 UTC (rev 14072) +++ core/trunk/documentation/manual/en-US/src/main/docbook/master.xml 2007-10-09 18:14:35 UTC (rev 14073) @@ -1,183 +0,0 @@ -<?xml version='1.0' encoding="iso-8859-1"?> -<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.3CR3//EN" - "../support/docbook-dtd/docbookx.dtd" -[ -<!ENTITY tutorial SYSTEM "modules/tutorial.xml"> -<!ENTITY architecture SYSTEM "modules/architecture.xml"> -<!ENTITY configuration SYSTEM "modules/configuration.xml"> -<!ENTITY persistent-classes SYSTEM "modules/persistent_classes.xml"> -<!ENTITY basic-mapping SYSTEM "modules/basic_mapping.xml"> -<!ENTITY collection-mapping SYSTEM "modules/collection_mapping.xml"> -<!ENTITY association-mapping SYSTEM "modules/association_mapping.xml"> -<!ENTITY component-mapping SYSTEM "modules/component_mapping.xml"> -<!ENTITY inheritance-mapping SYSTEM "modules/inheritance_mapping.xml"> -<!ENTITY session-api SYSTEM "modules/session_api.xml"> -<!ENTITY transactions SYSTEM "modules/transactions.xml"> -<!ENTITY events SYSTEM "modules/events.xml"> -<!ENTITY batch SYSTEM "modules/batch.xml"> -<!ENTITY query-hql SYSTEM "modules/query_hql.xml"> -<!ENTITY query-criteria SYSTEM "modules/query_criteria.xml"> -<!ENTITY query-sql SYSTEM "modules/query_sql.xml"> -<!ENTITY filters SYSTEM "modules/filters.xml"> -<!ENTITY xml SYSTEM "modules/xml.xml"> -<!ENTITY performance SYSTEM "modules/performance.xml"> -<!ENTITY toolset-guide SYSTEM "modules/toolset_guide.xml"> -<!ENTITY example-parentchild SYSTEM "modules/example_parentchild.xml"> -<!ENTITY example-weblog SYSTEM "modules/example_weblog.xml"> -<!ENTITY example-mappings SYSTEM "modules/example_mappings.xml"> -<!ENTITY best-practices SYSTEM "modules/best_practices.xml"> -]> - -<book lang="en"> - - <bookinfo> - <title>HIBERNATE - Relational Persistence for Idiomatic Java</title> - <subtitle>Hibernate Reference Documentation</subtitle> - <releaseinfo>3.2 cr3</releaseinfo> - </bookinfo> - - <toc/> - - <preface id="preface" revision="2"> - <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> - - &tutorial; - - &architecture; - - &configuration; - - &persistent-classes; - - &basic-mapping; - &collection-mapping; - &association-mapping; - &component-mapping; - &inheritance-mapping; - - &session-api; - &transactions; - &events; - &batch; - - &query-hql; - &query-criteria; - &query-sql; - &filters; - &xml; - - &performance; - - &toolset-guide; - - &example-parentchild; - &example-weblog; - &example-mappings; - - &best-practices; - -</book> -