I'm having problems with detached objects and LazyInitializationException on a Set with Hibernate 3. After having read through Hibernate in Action and tried every possibly combination of metadata, changing hibernate.max_fetch_depth, adding Hibernate.initialize( ) before closing the session etc, I started searching the web for more information on working with detached objects.

On the web, I found several suggestions for workarounds: like saving the session for the whole web request or using the Spring OpenSessionInViewFilter, but not much on how lazy loading works. I found at least two blogs that suggested not closing the session for the duration of a request, just to avoid getting a LazyInitializationException.

Does anybody know of a good explanation of how to get an object graph loaded (other than the HIA book)?

Here is the code that is giving me a headache, with class names changed to the HIA book example:



The following code gives a LazyInitializationException:



I have tried with criteria.setFetchMode("bids", FetchMode.EAGER), without success.

Jonas

I've got a similar problem to Jonas and I am wondering if it is a bug in Hibernate 3. The lazy attribute for sets seems to be being ignored or at least not being set up correctly.

If I load an object containing a set, close the hibernate session and then try to add an object to the set I get an

thrown.

This seems wrong to me. If I explictely access the set before closing the session then I get the correct result. I would have thought that setting the lazy attribute to false would have the same effect as accessing the set in the session but it doesn't appear to.

I'm using version 3.0.5 of Hibernate with Java 1.5.0_02.

You are mistaken.

OK - so I am mistaken in my assumptions about what lazy does.

How then do I guarantee that an object (containing a set) retrieved from the database is fully populated before I close the session?

I need to be able to do this so I can safely send the object to the UI layer in my application. I know I could do this by explicitly accessing the set after I retrieve it but that doesn't seem like a great thing to have to do.

<set lazy="false"> will guarantee this for a collection

<many-to-one lazy="false"> will guarantee this for a single-point association

get() will guarantee this for an entity instance just retrieved


Of course, an entity instance being available does not guarantee that its collections are available.

(Your confusion is that you don't know the difference between "a proxy" is not fetched and "a collection" is not fetched. Read error messages more carefully.)

It doesn't seem to for me.

Here's a snippet of the config file



and here is some code that fails.


the final line throws the Proxy initialization exception.

The user.addAlias() method is

Did you even read what I wrote?

It is a "proxy" that is uninitialized. Why? Because you use load() instead of get().

Thanks for that Gavin. It all starts to make a bit more sense now.

cheers.

Ask a question, and the answer immediately pops up in your head. In the end, my problem had nothing to do with lazy loading. I had added a method to set associations in both directions, inatvertently calling it setBid causing org.hibernate.LazyInitializationException: cannot access loading collection. I was thrown off by the fact that it was wrapped as a LazyInitializationException.

As a newcomer to Hibernate, the question of what is loaded when is by far the most confusing. The HIA book is extremely clear in describing most topics like mapping associations, HQL etc. I am still rather confused about what is loaded when, however. I looked through http://www.hibernate.org/37.html
before posting, finding only some partial explanations in http://www.hibernate.org/162.html. Part of my confusion is probably due to changes in defaults and naming between Hibernate 2 and 3. Time to start experimenting...

Jonas