Need explanation

gamby1980 · **Joined:** Sun Jul 27, 2008 10:56 am **Posts:** 17

Hi all,

Hibernate version:
3

Mapping documents:
I have a one to one association between class A and class B, the only direction for me is from A to B

Code between sessionFactory.openSession() and session.close():

Code:

try {
Session session = HibernateUtil.getSessionFactory().getCurrentSession();
session.beginTransaction();
            
List aList = session.createQuery("from A").list();

session.getTransaction().commit();

String desc = ((A)aList.get(0)).getB().getDescription();
}
catch(Exception e) {HibernateUtil.getSessionFactory().getCurrentSession().getTransaction().rollback();            
}        

Full stack trace of any exception that occurs:
org.hibernate.LazyInitializationException: could not initialize proxy - no Session
at org.hibernate.proxy.AbstractLazyInitializer.initialize(AbstractLazyInitializer.java:57)
at org.hibernate.proxy.AbstractLazyInitializer.getImplementation(AbstractLazyInitializer.java:111)
at org.hibernate.proxy.pojo.cglib.CGLIBLazyInitializer.invoke(CGLIBLazyInitializer.java:150)
....
Name and version of the database you are using:
MySql 5

My object A has a method to retrieve its associated object B, that is getB()
I have noticed that if I access a property of an object B after session commit where I loaded all objects A, I have that above exception.

I have also noticed that, If I call also following statement:
List bList = session.createQuery("from B").list();
after loading of A objects, then I can access all properties of all related B objects.

What I would like to understand is if there are other clever methods to load an Object and all its related object, or If I have to load all objects inside a Session.

Thanks in advance,
best regards
Gamby

Cameron McKenzie · **Posted:** Mon Jul 28, 2008 7:11 am

Quote:

What I would like to understand is if there are other clever methods to load an Object and all its related object, or If I have to load all objects inside a Session.

Yup, everything has to be loaded within an open session, otherwise, the associated objects are just proxies, and when you access them, you will have no active connection or session, creating a LazyInitializationException.

Using longer living Sessions, by employing something like the Open Session In View Pattern, will help you avoid LazyLoadingException problems.

You might find this tutorial on the inner workings of Hibernate somewhat enlightening. Check it out!

How Hibernate Works

gamby1980 · **Joined:** Sun Jul 27, 2008 10:56 am **Posts:** 17

Thank you very much,
I'll read that tutorial as soon as possible.

Best regards
Gamby

gamby1980 · **Joined:** Sun Jul 27, 2008 10:56 am **Posts:** 17

Hi Cameron,

I read your suggested article, but really it didn't help me to understand and solve m problem.

Let me you know that I'm not in a web context, that is I'm working on a rich client application with a local dbms, MySql.

The context in which I have that exception is:
- When app starts load objects A inside a transcation obviuosly, then commit
- A User can double click on one of those A objects to edit it.
- In this case, a dialog should appear showing all object A properties and all B object properties. remember that B is in one to one association with A.

I have that exception when, during dialog contents creation, I read object B properties to fill dialog widgets.

During dialog creation, there is no section and in general no hibernate concept involved.

After User click on ok button on dialog, then real update/insert happens.

Please, advise me about a solution to adopt for my specific context...I'm reading many tutorials and articles, but I really don't understand...

Thanks, best regards
Gamby