Hi,

I've recently had this issue during the migration of an application from hibernate 2 to hibernate 3, which I want to discuss on this forum with other Hibernate users:

I implemented the following form of entity serialization: during serialization, I write only the entity id (primary key) on the stream. For deserialization, I implement readResolve(), in which I get the current hibernate session, and get the entity based on the serialized primary key. This way, I have a clean serialization mechanism, not needing to bother with locking the entity with the session after deserialization, etc.

This mechanism worked fine for me with hibernate 2. However, with hibernate 3 I run into the following situation: if the entity has an unitialized proxy (e.g. was obtained through session.load), only the proxy gets serialized, without being initialized first. At deserialization, the proxy gets deserialized, but without readResolve being called, and the proxy is obviously not linked to the current session.

From my point of view, this is a bug in hibernate 3, as the proxy is not as transparent as it should be. I tried filling a bug report on this issue, but it was rejected (http://opensource2.atlassian.com/projects/hibernate/browse/HHH-1443).

What do you think? Is this really an issue with Hibernate 3, or not?
And does anybody have a sugestion for a workaround to achieve the serialization mechanism I described (and which worked in hibernate 2)?

Where do you call your readResolve() method from ?
I use the Extrenalizable interface in conjunction with an ObjectOuputStream to serialize objects loaded from Hibernate and it works transparently whether the proxy is initialized or not.

I don't call it, the JVM (normally) calls it. It's the standard Java serialization mechanism (see http://java.sun.com/j2se/1.4.2/docs/api/java/io/Serializable.html).
I have to say I have not tried to implement Externalizable, but with Serializable it's only the uninitialized proxy that gets serialized, and writeObject is not even called.

First, you may try setting the lazy-load default to false in each of your mappings. Hibernate 3 differs from Hibernate 2 in that it has lazy loading (via CGLIB-generated proxies) as the default. Your old system probably fully loaded the object graph without proxies.

More generally, we have not found that trying to get proxies to work in a distributed way is feasible. (and beleive me we tried). The standard pattern seems to be that you touch/initialize all the stuff you need during the server call while connected to the session. Setting lazy=false in all the right places is just one way to force that.

Again, set lazy=false at the class level is easiest so you don't need to mark every relationship as non-lazy.

Nope, it did not. I use lazy load and proxies almost always - I carefully monitored the generated SQL queries. Using lazy=false is not an option for me, neither is disableing proxies.
And I am really sure that proxy serialization worked smooth in hibernate 2, which I can not say about Hibernate 3.

You must use custom proxies to implement this hack in Hibernate3, hibernate replaces uninitialized proxy with fake handle itself.

Thanks for the suggestion.
Any hints where I should start digging from? I do not remember finding anything about custom proxies in Hibernate manual...

See custom tuplizer.