Hibernate Many to Many association does not update database

[Ahmet Degirmenci]

I am trying to insert record to a database using hibernate many to many association. There is something I miss but could not figure it out.
Here are my files

User.hbm.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="firstfm">
    <class name="User" table="User">
        <id column="username" name="username" type="string"/>
        <property column="password" insert="true" name="password" not-null="true" type="string" update="true"/>
        <property column="nationality" insert="true" name="nationality" not-null="true" type="string" update="true"/>
        <property column="gender" insert="true" name="gender" not-null="true" optimistic-lock="false" type="string" update="true"/>
        <set cascade="all" inverse="true" name="likedPerformers" table="likesPerformer" lazy="false">
            <key column="username"/>
            <many-to-many class="Performer" column="performerName" unique="true"/>
        </set>
        <set  name="likedMusicTypes" cascade="all" table="likesmusictype" lazy="false" >
            <key column="username"/>
            <many-to-many column="musicType" unique="true"  class="MusicType" />
        </set>
    </class>
</hibernate-mapping>    

MusicType.hbm.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="firstfm">
    <class name="MusicType" table="MusicType">
        <id column="name" name="name" type="string"/>
  
        <set name="likingUsers" lazy="false" table="likesmusictype" inverse="true">
            <key column="musicType"/>
            <many-to-many column="username" class="User"/>
        </set>
    </class>
</hibernate-mapping>    

The code piece that is supposed to make update(which does not)

 @Action
    public void addMusicType() {
        if (!allList.isSelectionEmpty()) {
            MusicType selected = (MusicType) allList.getSelectedValue();
            if (!likedMusicTypes.contains(selected)) {
                try {
                    //currentUser is an instance of User
                    //selected is an instance of MusicType
                    currentUser.getLikedMusicTypes().add(selected);
                    persistenceManager.update(currentUser);
                } catch (Exception ex) {
                    WarningPopUp.showWarning(ex.getMessage());
                }
                //refresh();
            }
        }
    }   

however the following code does :

 HibernateUtil hu = new HibernateUtil();
	
		User user = (User) hu.get(User.class, "Cahin");
		MusicType mT= (MusicType) hu.get(MusicType.class, "Jazz");
		user.getLikedMusicTypes().add(mT);	
		hu.update(user);   

The persistenceManager and hu is instances of same Class : HibernateUtils the update function is here

public void update(Object object) throws Exception {
        Transaction tx = null;
        try {
            tx = session.beginTransaction();
            session.update(object);
            session.flush();
            tx.commit();
        } catch (HibernateException hex) {

            if (tx != null) {
                tx.rollback();
            }
            throw new Exception(hex.getMessage() + CAUSE_DELIMITER + hex.getCause().getMessage());
        } finally {
        }
    }    

My POJO s and database is generated by hibernate tools

If you have an idea, please guide me. Thanks.

[Mark Spritzler]

It is all about managed persistence. In the second example the related object is being managed by Hibernate. In the first example it is not.

In the first example you would be required to set both sides of the relationship. You many to many mapping is bi-directional, and in your first example you set only one of those directions.

In the second example since both sides of the association is loaded via the Session and therefore both being managed, they have both sides set.

So because only one side is set in the first example, it only knows how to update that side of the relationship and not the other side. The other side would update that side of the relationship in the database.

Hope that helps clear things up.

Basically if you add

currentUser.getLikedMusicTypes().add(selected);
selected.setUser(currentUser);

instead, then you set both sides and the persist call will update the MusicTypes side.

The best approach is to have an user.addMusicType(User user) or musicType.addUser(MusicType) method on the code and in the add method make sure that the other side is also set.

Mark

[Ahmet Degirmenci]

After reading your post and the part of Hibernate Documentation about bi-directional associations I understand the problem.
(Also realized that the "inverse" in the User.hbm.xml should not be there at all)
Thank you very much.