Many-to-many bi-directional relationship

[czy11421]

I am trying Many-to-many bi-directional relationship, but failed.

Event e = new Event();
		e.setEventId(1);
		this.getHibernateTemplate().save(e);		
		
		Speaker s1 = new Speaker();
		s1.setSpeakerId(1);
		s1.setSpeakerName("s1");
		this.getHibernateTemplate().save(s1);		
		
		Speaker s2 = new Speaker();
		s2.setSpeakerId(2);
		s2.setSpeakerName("s2");
		this.getHibernateTemplate().save(s2);		
		
		List<Speaker> list = new ArrayList<Speaker>();
		list.add(s1);
		list.add(s2);
		e.setSpeakerList(list);
		this.getHibernateTemplate().update(e);
		
		DetachedCriteria criteria = DetachedCriteria.forClass(Speaker.class);  
		criteria.add(Restrictions.eq("speakerId", new Long(1)));
		
		List results = this.getHibernateTemplate().findByCriteria(criteria);
		Speaker g = (Speaker)results.get(0);
		System.out.println(g);

/////////////
 <class name="data.Event" table="mts_event" >
    	<cache usage="read-write"/>    	
        <id name="eventId" column="eventId" unsaved-value="-1">
            <generator class="assigned"/>
        </id>        
        <property name="eventName"/>     	
     	<list name="speakerList" table="mts_event_speaker">
           <key column="eventId"/>
           <index column="idx"/>
           <many-to-many column="speakerId" class="data.Speaker"/>
     	</list>
    </class>
    
    <class name="data.Speaker" table="mts_speaker" >
    	<cache usage="read-write"/>    	
        <id name="speakerId" column="speakerId" unsaved-value="-1">
            <generator class="assigned"/>
        </id>        
        <property name="speakerName"/>     	
     	<list name="eventList" table="mts_event_speaker">
           <key column="speakerId"/>
           <index column="idx"/>
           <many-to-many column="eventId" class="data.Event"/>
     	</list>
    </class>

Now the relationship data is saved into mts_event_speaker. Event and Speaker are saved.

But I want to load Speaker g. I think g should have not-null eventList, because the relationship data is in database.

Hibernate: insert into mts_event_speaker (eventId, idx, speakerId) values (?, ?, ?)
2007-07-13 14:16:03,027 DEBUG [org.hibernate.type.LongType] - binding '1' to parameter: 1
2007-07-13 14:16:03,027 DEBUG [org.hibernate.type.IntegerType] - binding '1' to parameter: 2
2007-07-13 14:16:03,027 DEBUG [org.hibernate.type.LongType] - binding '2' to parameter: 3
2007-07-13 14:16:03,027 DEBUG [org.hibernate.persister.collection.AbstractCollectionPersister] - done inserting collection: 2 rows inserted
2007-07-13 14:16:03,027 DEBUG [org.hibernate.jdbc.AbstractBatcher] - Executing batch size: 2
2007-07-13 14:16:03,043 DEBUG [org.hibernate.jdbc.Expectations] - success of batch update unknown: 0
2007-07-13 14:16:03,043 DEBUG [org.hibernate.jdbc.Expectations] - success of batch update unknown: 1
2007-07-13 14:16:03,043 DEBUG [org.hibernate.jdbc.AbstractBatcher] - about to close PreparedStatement (open PreparedStatements: 1, globally: 1)
2007-07-13 14:16:03,043 DEBUG [org.hibernate.jdbc.AbstractBatcher] - closing statement
2007-07-13 14:16:03,043 DEBUG [org.hibernate.jdbc.ConnectionManager] - registering flush end
2007-07-13 14:16:03,043 DEBUG [org.hibernate.event.def.AbstractFlushingEventListener] - post flush
2007-07-13 14:16:03,058 DEBUG [org.hibernate.jdbc.AbstractBatcher] - about to open PreparedStatement (open PreparedStatements: 0, globally: 0)
2007-07-13 14:16:03,058 DEBUG [org.hibernate.SQL] - select this_.speakerId as speakerId8_0_, this_.speakerName as speakerN2_8_0_ from mts_speaker this_ where this_.speakerId=?
Hibernate: select this_.speakerId as speakerId8_0_, this_.speakerName as speakerN2_8_0_ from mts_speaker this_ where this_.speakerId=?
2007-07-13 14:16:03,058 DEBUG [org.hibernate.jdbc.AbstractBatcher] - preparing statement
2007-07-13 14:16:03,058 DEBUG [org.hibernate.type.LongType] - binding '1' to parameter: 1
2007-07-13 14:16:03,105 DEBUG [org.hibernate.jdbc.AbstractBatcher] - about to open ResultSet (open ResultSets: 0, globally: 0)
2007-07-13 14:16:03,105 DEBUG [org.hibernate.loader.Loader] - processing result set
2007-07-13 14:16:03,105 DEBUG [org.hibernate.loader.Loader] - result set row: 0
2007-07-13 14:16:03,105 DEBUG [org.hibernate.type.LongType] - returning '1' as column: speakerId8_0_
2007-07-13 14:16:03,105 DEBUG [org.hibernate.loader.Loader] - result row: EntityKey[data.Speaker#1]
2007-07-13 14:16:03,105 DEBUG [org.hibernate.loader.Loader] - done processing result set (1 rows)
2007-07-13 14:16:03,105 DEBUG [org.hibernate.jdbc.AbstractBatcher] - about to close ResultSet (open ResultSets: 1, globally: 1)
2007-07-13 14:16:03,105 DEBUG [org.hibernate.jdbc.AbstractBatcher] - about to close PreparedStatement (open PreparedStatements: 1, globally: 1)
2007-07-13 14:16:03,105 DEBUG [org.hibernate.jdbc.AbstractBatcher] - closing statement
2007-07-13 14:16:03,121 DEBUG [org.hibernate.loader.Loader] - total objects hydrated: 0
2007-07-13 14:16:03,121 DEBUG [org.hibernate.engine.StatefulPersistenceContext] - initializing non-lazy collections
2007-07-13 14:16:03,121 DEBUG [org.springframework.orm.hibernate3.HibernateTemplate] - Not closing pre-bound Hibernate Session after HibernateTemplate
data.Speaker@dab859[speakerId=1,speakerName=s1,eventList=<null>]

Another question, in above java coding, if I use saveOrUpdate, it doesn't work. I don't know why.

What is your idea ?

Thanks.

[dr_pompeii]

you should ask this in Data Access section

[ozGuy]

many-to-many usually gets broken down into one-to-manu and many-to-one relationship using a third table. look at hibernate docs for some example.

You need to specify cascade attribute on the collections and then you can simple say events.saveOrUpdate() and this will save/update everything events is linked to.

[karldmoore]

This has been reposted here...........
http://forum.springframework.org/showthread.php?t=41409