Once again: LazyInitialization

[Oliver Gierke]

Hi folks,

I'm trying to do the following and don't know how to avoid a lazy initialization exception:

I have 2 POJOs that are in a bidirectional n:m relation and store each others references in a list. I have implemented DAOs for both of them and want to access the via a service facade. Now I've written a JUnit test to test my service. One method covers the following use case:

Assign all A's to B's. I tried to do something like this:

List<A> list = serviceFacade.getAll() //returns all Entries frm the DB
Iterator<A> it = list.iterator();
while (it.hasNext())
{
	A objectA = it.next();
						
	B objectB = newB();
	objectB.setName("B "+objectA.getId());
			
	serviceFacade.assignBToA(objectB, objectA);
}

the serviceFacade's method looks as follows:

objectA.addB(objectB);
aDAO.save(objectA);

the classA's method addB looks as follows:

this.listOfBs.add(objectB);
objectB.getAs.add(this);

The lazy initializaton exception is thrown in

this.listOfBs.add(objectB);

what seems to make sense, as the list is marked to be lazily fetched in the Hibernate mapping file.

My question is where and how to reattach the objects to a new session without affecting business code.

I've tried to introduce a method

reattach(BO oBO)
{
	getHibernateTemplate.saveOrUpdate(oBO);
}

to my DAOs and call them in assignBToA before the business method call (objectA.addB(objectB), but I still get the lazy init exception.

Any tutorials i can find, talk about the OpenSessionInViewFilter but i don't see a way to use it in a JUnit test.

Regards,

Ollie

[tomSIEM]

Hi Oliver!
I have also this problem. The reason is that every collection in hibernate has a session. in a detached object the session ist closed. when you will access to the collection the object in the collection can not be fetched because no session is opened for this collection.
this is only the reson but I do not know a answer how it could works.
I have tried to reinitialize de collection with

Hibernate.initialize(obj)
Hibernate.initialize(obj.getCollection())

but I get the HibernateException with the message disconnected Session

so maybe anyone can help us, because Lazy-Loading is e very complicating theme...

thanx!!
tom

[tomSIEM]

Hello Oliver!
in the Hibernate Forum I get the following help (thanx to sw79)

public void addAToB(A a, B b) {
    Session s = this.getSession();
    B newb = (B)s.get(b.getClass(), b.getId());
    newb.getAs().add(a);
    this.saveOrUpdate(b);
  }

I hope you can fix your problem

Maybe you get the session in this way:

 Session s = this.getHibernateTemplate().getSessionFactory().openSession();

than you hav a new session opened, but in a DAO object this is not necessary.

Good Luck!

tom

[Costin Leau]

I recommend to take a look at
org.springframework.test.AbstractTransactionalData SourceSpringContextTests
which is made exactly for your case. It will open a transaction for each test
and roll it back at the end. This is not just very useful when doing
integration testing (like you are) but also keeps a session opened for the duration
of your tests. It also contains endTransaction() and startNewTransaction()
methods which allows you test lazy inits or how your services behave
after crossing different transaction bounderies.
The test has some nice documentation inside the reference and you
take a look at the junit tests inside Spring for more info. It has also
been discussed several times on the forum.