suppose i have two tables: User and Role which have many-2-many relationships.

the third mapping table is called REL_USER_ROLE

in user.hbml.xml

<set name="roles"
table="REL_USER_ROLE"
cascade="save-update"
lazy="false"
sort="unsorted">

<key column="USERID"/>
<many-to-many class="package.Role"
column="ROLEID"
not-found="ignore">
</many-to-many>
</set>

The problem is that i need insert some additional information to the relation table (rel_user_role), e.g. add one column "status" where value is fixed (say it is "undeleted" for User).

how can i map the third column in hbm?

search for <composite-element> in the reference.pdf

http://www.hibernate.org/hib_docs/v3/reference/en/pdf/hibernate_reference.pdf

See the Caveat Emptor example (originally written for the book Hibernate In Action) mapping CategorizedItem for how to do this.

You can download the example files from http://caveatemptor.hibernate.org/2.html

You can buy the ebook from there too.


The mapping file used in the example is pasted below.

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping SYSTEM "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="org.hibernate.ce.auction.model">
<!--

Mapping file for the CategorizedItem class of CaveatEmptor.

This is really a very special mapping. The CategorizedItem class
represents an association table. The ER model for this is really
a many-to-many association, but instead of two entities and two
collections, we mapped this as two one-to-many associations between
three Java classes. One of the motivation for this are the additional
attributes on the association table (not only two FKs): username
and creation date.

This class is the entity in the middle, between Category and Item.
You can see that it has references to both. The trick is the usage
of update="false" insert="false" on the <many-to-one> mapping
elements. The foreign/primary key columns of the association table
is therefore managed by the <key-property> mappings in the composite
key.

Note that the composite key is encapsulated in an inner class, which
simplifies the implementation of equals/hashCode. We recommend to
always use a separate composite key class.

@author Christian Bauer <christian@hibernate.org>

-->
<class name="CategorizedItem" table="CATEGORIZED_ITEM" mutable="false">
<composite-id name="id" class="CategorizedItem$Id" access="field">
<key-property name="categoryId" access="field" column="CATEGORY_ID"/>
<key-property name="itemId" access="field" column="ITEM_ID"/>
</composite-id>
<property name="dateAdded" column="ADDED_ON" type="timestamp" not-null="true" access="field"/>
<property name="username" column="ADDED_BY_USER" type="string" not-null="true" access="field"/>
<many-to-one name="category" column="CATEGORY_ID" not-null="true" access="field" insert="false" update="false"/>
<many-to-one name="item" column="ITEM_ID" not-null="true" access="field" insert="false" update="false"/>
</class>
</hibernate-mapping>

thanx for ur reply.

Composite ID, that is it.