I have a requirement to support attributes in an Association table being used in many-to-many association. For example, consider the many-to-many relationship from Group and User classes, Group can contain multiple sub Groups as well as multiple Users. Also, Users and Groups can be children of multiple Parent Groups.

I have a User class(in User table), Group class(in Group table) and an association table group_membership (with no association class). The group_membership table can contain the following columns:

parent_group_id NOT NULL(foreign key to Group table)
child_group_id NULL (foreign key to Group table)
child_user_id NULL (foreign key to User table)
permissions (additional relationship attribute required)

How do I specify the mapping in Group class to get/set the childGroups (including the relationship attribute permissions)?

Thanks in advance.

Have a look at section 7.2 of the reference guide, the second example.
And you can use the search tool of the forum. I remember answerig that question... yesterday ;-)

Thanks for reply.

I have one more question on the same topic.
If my association table group_membership has the following attributes :

parent_group_id NOT NULL(foreign key to Group table)
child_id NULL NOT NULL (Not a foreign key but the id will be either pointing to Group table or User table)
child_type NOT NULL ('U' - means child is a User, 'G' - means child is a Group)
permissions (additional relationship attribute required )

How do I specify the many-to-many relationship from Group to User using the above mentioned group_membership table structure?

Use <any> inside the <composite-element> mapping.

Gavin,

<composite-element> does not accept <any> in it. I get the following error if I add any inside <composite-element>:

ERROR [Thread-4] 2003-12-23 23:42:18,735 - net.sf.hibernate.util.XMLHelper - Error parsing XML: XML InputStream(180) The content of element type "composite-element" must match "(parent?,(property|many-to-one|nested-composite-element)*)".

Even I verified the dtd, it doesn't accept it. Here is my mapping:

<set name="Persons" table="groupmembership" lazy="true" inverse="true">
<key column="group_id"/>
<composite-element class="net.sf.hibernate.examples.quickstart.GroupMembership">
<any name="members" id-type="string" meta-type="net.sf.hibernate.examples.quickstart.GroupTypeMapper">
<column name="child_type"/>
<column name="child_id"/>
</any>
</composite-element>
</set>


Any thoughts?

Thanks

Try to update the DTD in your jar to support it. From a very quick look, it *might* work (at least it will bind properly).

Submit a bug to Jira in order to follow this topic.

Updating the DTD worked. I looked at the SQLs that were executed, and I noticed that there was one SQL to retrieve all rows from the relationship table for a group id (I specified in my code) and for each record in the relationship table based on the child type (User or Group), one select SQL issued to retrieve either the from the User table or from the Group table.

Is there anyway, hibernate would be able to retrieve all the members of the group(users and child groups) in one SQL by joining the relationship table, user and group tables using the <composite-element> and <any> constructs?

Thanks

I don't know about the any, but try with lazy="false"

It doesn't help with lazy="false".

Nope. <any> does not support outer join loading (this is not unreasonable).

Better to make the associated class with lazy="true".