I have a situation in which I need to have Groups within Groups and its a many-to-many relationship which means the groups can have other groups and the groups could be contained by multiple groups. I've been trying to implement this in Hibernate with no luck. Here is what I have

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- Generated Nov 21, 2006 11:48:22 AM by Hibernate Tools 3.2.0.beta6a -->
<hibernate-mapping>
<class name="Group" table="App_Group" schema="dbo" catalog="PI_WEBSERVICE_TEST">
<id name="id" type="string">
<column name="id" />
<generator class="assigned" />
</id>
<property name="name" type="string">
<column name="name" length="50" />
</property>
<property name="desc" type="string">
<column name="description" length="50" />
</property>
<property name="createdBy" type="string">
<column name="createdBy" length="50" />
</property>
<property name="createdDate" type="timestamp">
<column name="createdDate" length="23" />
</property>

<set name="groups" inverse="false"
table="ParentChildGroupRelation"
lazy="false"
cascade="all">
<key column="parentGroupId"/>
<many-to-many class="Group" column="childGroupId"/>
</set>


I have defined a table named ParentChildGroupRelation that has the parentGroupId and childGroupId having a foreign key relationship with the groupId from the Group table. When I try to add a group to an existing group and try to save it no exception is thrown but nothing gets saved in the DB. My cascade options seem to be ok. Did anyone implement this kind of relationship before and if so can you please share your thoughts on this.

I think you need to associations inside your Group POJO: childGroups and parentGroups.

The mapping would be something like:


<class name="Group" table="App_Group" schema="dbo" catalog="PI_WEBSERVICE_TEST">
(...)
<set name="parentGroups" table="ParentChildGroupRelation">
<key column="childgroup_id"/>
<many-to-many column="parentgroup_id" class="Group"/>
</set>
<set name="childGroups" inverse="true" table="ParentChildGroupRelation">
<key column="parentgroup_id"/>
<many-to-many column="childgroup_id" class="Group"/>
</set>
(...)

this should work fine. Don't declare an inverse end! By doing so, hibernate will not save the childs / parents