[hibernate-users] Many-to-Many attributed mapping issue
Hello. I am new to this list but I've scoured the web for a solution
and cannot find a solution to this issue.
I am using Hibernate 3.x with XML mapping files but under Grails/GORM.
I have two tables: Groups and Users with a M-M correlation table called
GroupsUsers. There are a few extra attributes on the GroupsUsers table
like "role". The problem is that I need to be able to create a new
Group along with some new GroupsUsers instances and save all of them
when the Group (newly instantiated or freshly loaded) is saved.
Conversely, when a User is saved (new or existing), any GroupsUser
instances need to be saved along with it. I want Hibernate to do all
the work.
The problem is that the GroupsUsers instance needs a foreign key to the
Group but the Group is not yet saved. I thought the cascade option on
the groupsUsers association would take care of that but it doesn't.
Maybe it's a problem with the composite primary key? I tried modelling
that with just the id's as "long" values but that didn't work.
Ideas? Or better yet, this must be a fairly common design pattern so
sample code would be ideal if you have it...
GroupsUsers.hbm.xml:
===============
<hibernate-mapping>
<class name="com.mycompany.GroupsUsers" table="GROUPSUSERS">
<composite-id class="com.mycompany.GroupsUsersPK"
name="groupsUsersPK">
<key-many-to-one name="user" class="com.mycompany.User"
column="USER_ID"/>
<key-many-to-one name="group" class="com.mycompany.Group"
column="GROUP_ID"/>
</composite-id>
<property name="role" column="ROLE" type="string"/>
<property name="active" column="ACTIVE"
type="yes_no"/>
<many-to-one name="group" class="com.mycompany.Group"
column="GROUP_ID"
not-null="true" insert="false" update="false"/>
<many-to-one name="user" class="com.mycompany.User"
column="USER_ID"
not-null="true" insert="false" update="false"/>
</class>
</hibernate-mapping>
Groups.hbm.xml:
============
<hibernate-mapping>
<class name="com.mycompany.Group" table="GROUPS">
<id name="id" column="ID" type="long">
<meta attribute="use-in-tostring">true</meta>
<generator class="seqhilo">
<param name="sequence">keyseedsequence</param>
<param name="max_lo">999</param>
</generator>
</id>
<timestamp name="updated" column="UPDATED" />
<property name="name" column="NAME"
type="string"><meta
attribute="use-in-tostring">true</meta></property>
<property name="description" column="DESCRIPTION"
type="string"/>
<set name="groupsUsers" table="GROUPSUSERS"
cascade="all,delete-orphan"
inverse="true">
<key column="GROUP_ID"/>
<one-to-many class="com.mycompany.GroupsUsers"/>
</set>
</class>
</hibernate-mapping>
The Users.hbm.xml mapping is similar to Groups.hbm.xml
Example save:
Group group = new Group();
group.setName("Test");
group.setDescription("Just testing...");
User user = User.findById(123456);
GroupsUsers gu = new GroupsUsers();
gu.setRole("Principal");
gu.setGroup(group);
gu.setUser(user);
GroupsUsersPK pk = new GroupsUsersPK(); // composite primary key
pk.setGroup(group);
pk.setUser(user);
gu.setGroupsUsersPK(pk);
group.getGroupsUsers().add(gu);
group.save(flush:true); // GORM save and flush