Hi,

I am trying to make a many to many relationship that involves 3 tables, 'Student', 'Faculty' and 'course'. Here the many to many relationship is between faculty and student. Mapping table is 'course'. This is how I have the mapping

<class name="com.nielsenmedia.manytomany.entities.Course" table="course" dynamic-update="true" dynamic-insert="true" >
<composite-id>
<key-many-to-one class="com.nielsenmedia.manytomany.entities.Student"
name="student" column="STUDENT_ID"/>
<key-many-to-one class="com.nielsenmedia.manytomany.entities.Faculty" name="faculty"
column="FACULTY_ID"/>
</composite-id>
</class>

<class name="com.nielsenmedia.manytomany.entities.Faculty" table="faculty" dynamic-update="true" dynamic-insert="true" > <id name="facultyID" type="java.lang.Long" column="FACULTY_ID" unsaved-value="0">
<generator class="identity"/>
</id>
<property name="facultyName">
<column name="FACULTY_NAME" sql-type="varchar(20)"/>
</property>
<set name="students" table="course" inverse="true" cascade="save-update">
<key column="FK_FACULTY_ID"/>
<many-to-many class="com.nielsenmedia.manytomany.entities.Student"
column="FK_STUDENT_ID"/>
</set>
</class>

<class name="com.nielsenmedia.manytomany.entities.Student" table="student" dynamic-update="true" dynamic-insert="true" >
<id name="studentID" type="java.lang.Long" column="STUDENT_ID" unsaved-value="0">
<generator class="identity"/>
</id>
<property name="studentName">
<column name="STUDENT_NAME" sql-type="varchar(20)"/>
</property>
<set name="faculties" table="course" inverse="true" cascade="save-update">
<key column="FK_STUDENT_ID"/>
<many-to-many class="com.nielsenmedia.manytomany.entities.Faculty"
column="FK_FACULTY_ID"/>
</set>
</class>

When I create an instance of Faculty and add students to it and save, it saves both the Faculty and student table but not the course table. I expect it to create rows for the many-to-many association via 'course' table. Forgive if I miss anything so basic.

Regards,
-Jay.

Hi.
To be honest, I have no idea should your mapping work or not :)
First things come in mind looking at your code are:
1. you did not specify "unsaved-value" for your Course class. I suppose this it is mandatory for <composite-id> (see "8.4. Using cascading update()")
2. Make sure your Course class implements hashCode & equals. Mandatory for <composite-id> too. (see "6.4. As Composite Identifiers"
)

Also I have noticed none of your sets is lazy. That means when object is loaded, its set is also initialized which causes in turn loadind of other sets and so on. This may be VERY inefficient.

You have mapped both ends of the collection inverse="true".

As cavin and dimas said I gave the unsaved-value property, implemented the equals method, removed inverse property at both the ends and modified the composite-id as below
<class name="com.nielsenmedia.manytomany.entities.Course" table="course" dynamic-update="true" dynamic-insert="true" unsaved-value="any">
<composite-id unsaved-value="any">
<key-property name="studentID" column="FK_STUDENT_ID" type="long"/>
<key-property name="facultyID" column="FK_FACULTY_ID" type="long"/>
</composite-id>
</class>

and also the domain object accordingly.

I get rows created for every row that is created in the many to many end.

Now if I have attributes defined for the mapping table 'course' how will I go about providing values for these attributes. What if any of this attribute is not-null?

Take a look at documentation section 7 "Components" and particulary to 7.2 "In collections" - http://www.hibernate.org/hib_docs/refer ... nents-s2-2