inverse=true in many-to-many doubt

[sudheer kiran]

i have two hbm files person and event
i have declared a many-to-many relation on both files and declared inverse="true" in event.hbm.xml
every thing is working fine on Person
but in event none of these are working
1---event.setParticipants(set);
2---event.getParticipants().add(person);

if i remove inverse="true" then its working.
what actually is inverse.
thanks.

[Christian Dillinger]

Can you please post your mappings?

This works for me:

  
<hibernate-mapping package="de">

	<class name="Person">

		<id name="personId">
			<generator class="seqhilo">
				<param name="sequence">PersonSeq</param>
				<param name="max_lo">100</param>
			</generator>
		</id>

		<property name="personName" not-null="true" />

		<set name="events" table="PERSON_EVENT" cascade="save-update">
			<key column="personId" />
			<many-to-many class="Event" column="eventId" />
		</set>
	</class>

</hibernate-mapping>

<hibernate-mapping package="de">

	<class name="Event">

		<id name="eventId">
			<generator class="seqhilo">
				<param name="sequence">EventSeq</param>
				<param name="max_lo">100</param>
			</generator>
		</id>

		<property name="eventName" not-null="true" />

		<set name="persons" table="PERSON_EVENT" inverse="true" cascade="save-update">
			<key column="eventId" />
			<many-to-many class="Person" column="personId" />
		</set>
	</class>

</hibernate-mapping>

To maintain both side of the association. In Person:

	public void addEvent(Event event) {
		if (this.events == null) {
			this.events = new HashSet<Event>();
		}
		this.events.add(event);
		event.addPerson(this);
	}

In Event:

	public void addPerson(Person person) {
		if (this.persons == null) {
			this.persons = new HashSet<Person>();
		}
		this.persons.add(person);
	}

[sudheer kiran]

hi thanks for the reply,its working but what if you wanted to add a collection of participants to event.
event.setParticipants(participants); is not working
am i need to use a for loop.

[sudheer kiran]

which ever side i declare inverse=true,on that side(say event.hbm.xml or person.hbm.xml ) the setCollection() method doesnt inserting any values.

[Christian Dillinger]

In my sample Event is marked as inverse.

This code:

			Session session = factory.openSession();
			Transaction trans = session.beginTransaction();

			Person p1 = new Person();
			p1.setPersonName("Name1");
			Person p2 = new Person();
			p2.setPersonName("Name2");
			Person p3 = new Person();
			p3.setPersonName("Name3");
			
			Event e1 = new Event();
			e1.setEventName("Event1");
			Event e2 = new Event();
			e2.setEventName("Event2");
			Event e3 = new Event();
			e3.setEventName("Event3");
			
			p1.addEvent(e1);
			p1.addEvent(e2);
			
			p2.addEvent(e2);
			p2.addEvent(e3);
					
			Set<Event> eventsForP3 = new HashSet<Event>();
			eventsForP3.add(e1);
			eventsForP3.add(e2);
			eventsForP3.add(e3);
			
			p3.setEvents(eventsForP3);
			
			session.save(p1);
			session.save(p2);
			session.save(p3);
			
			session.save(e1);
			session.save(e2);
			session.save(e3);
			
			trans.commit();
			session.close();
			
			Session sessRead = factory.openSession();
			Criteria crit = sessRead.createCriteria(Person.class);
			crit.addOrder(Order.asc("personName"));
			
			List<Person> persons = crit.list();
			for(Person person : persons){
				System.out.println(person);
				Set<Event> events = person.getEvents();
				for(Event event : events){
					System.out.println("  " + event);					
				}				
			}
			sessRead.close();

lists:

[Person: 101 / Name1]
  [Event: 101 / Event1]
  [Event: 102 / Event2]
[Person: 102 / Name2]
  [Event: 103 / Event3]
  [Event: 102 / Event2]
[Person: 103 / Name3]
  [Event: 103 / Event3]
  [Event: 101 / Event1]
  [Event: 102 / Event2]

Please post your code and the result.

[sudheer kiran]

Event.hbm.xml

    
<hibernate-mapping package="hb.dao">
	<class name="Event" table="events">
		<id name="id" column="event_id">
			<generator class="assigned"></generator>
		</id>
		<property name="date" column="event_date" type="timestamp"></property>
		<property name="title" />

		<set name="participants" table="PERSON_EVENT" inverse="true" lazy="false" cascade="save-update">   
			<key column="EVENT_ID" />
			<many-to-many  column="PERSON_ID" class="Person" />
		</set>

	</class>

</hibernate-mapping>

Person.hbm.xml

    <hibernate-mapping package="hb.dao">
	<class name="Person" table="PERSON">
		<id name="id" column="PERSON_ID">
			<generator class="assigned"></generator>
		</id>
		<property name="age" type="int" />
		<property name="firstName" column="FIRST_NAME" type="string" />
		<property name="lastName" column="LAST_NAME" type="string" />

		<set name="events" table="PERSON_EVENT" lazy="false" cascade="save-update">
			<key column="PERSON_ID" />
			<many-to-many column="EVENT_ID" class="Event"></many-to-many>
		</set>
	</class>
</hibernate-mapping>

my class method

   public void addPersonToEvent(){
		try{
			
			PersonDAO personDAO = new PersonDAO();
			EventDAO eventDAO = new EventDAO();
			Person person = personDAO.findById(1);
			Event event = new EventDAO().findById(1);
			Set participants = new HashSet();
			participants.add(person);
			//event.setParticipants(participants); //does not work when declared inverse="true"
			//event.getParticipants().add(person);
			event.addToParticitants(person);  //this only working but i need to add collection of persons
			eventDAO.saveOrUpdate(event);

		}
		catch(Exception e){
			System.out.println(e);
		}
	}			 

after i compile,there are no errors,
only select statements are displayed nto insert or updates.
no change to data base.

[Christian Dillinger]

Your code:

#    public void addPersonToEvent(){  
#         try{  
#               
#             PersonDAO personDAO = new PersonDAO();  
#             EventDAO eventDAO = new EventDAO();  
#             Person person = personDAO.findById(1);  
#             Event event = new EventDAO().findById(1);  
#             Set participants = new HashSet();  
#             participants.add(person);  
#             //event.setParticipants(participants); //does not work when declared inverse="true"  
#             //event.getParticipants().add(person);  
#             event.addToParticitants(person);  //this only working but i need to add collection of persons  
#             eventDAO.saveOrUpdate(event);  
#   
#         }  
#         catch(Exception e){  
#             System.out.println(e);  
#         }  
#     }         

It's obvious that event.setParticipants(participants) cannot trigger an insert when Event is mapped as inverse. Because Hibernate ignores changes made on that set. You can implement setParticipants(participants) like that:

	public void setParticipants(Set<Person> persons) {
		this.persons = persons;
		for(Person person : persons){
			person.getEvents().add(this);
		}
	}

So you change the list on the non-inverse-side. Hibernate should trigger the inserts then.

[sudheer kiran]

working fine but still i got another issue

org.hibernate.NonUniqueObjectException: a different object with the same identifier value was already associated with the session: [hb.dao.Event#3]

entries in person_event table are
1-1
1-2
1-3

when i try to insert 2-2 or 2-3 i get that exception

[Christian Dillinger]

That exception occurs when you try to put an entity that is either in detached state or read by another session (let's say sessionA) into sessionB where it is already "known". So Hibernate cannot decide which version it should handle as current state. (Merging is the solution...)
But without seeing the complete code it's not possible to find a real solution for that particular case.

[sudheer kiran]

hi thanks for the help,now its working when i used session instead of DAOs.