Hallo,

Why are detached entities with lazy related collections not converted to their "origin" Class structure, but converted to another class structure ? The conversion of Collection to PersistentSet gives problems with serialisation of the detached objects. Is this a bug or feature in hibernate / EJB3 ?!? My session is closed, so the object is detached.

Thanks !

This is a feature, otherwise we woudn't know what to update and what not to update during reattachment

But what is the correct way to return a detached entity to a remote client ?!? The only way now is to set all the relations to null :

entity.setChildren(null)

otherwise the serialisation of the related collections etc. throws an exception. This is not a nice way to achieve the serialisation is it ?!? Are there standards for this pattern ?

Thanks !

Have Hibernate jar on the client side

Dear emmanuel,

Thanks for your thoughts !

The exception is thrown on the server side while serializing the entity. I'm using Adobe Flex 2.0 with Remote Java objects. The flash client call a remote Java object on the flex server (JBoss) and serialises the result to it's own format for transporting the Java object to the Flash client.

So the problem is that the flex server cannot serialise the java object because of the "PersistentSet" attribute type.

The case is very common I think :

1) With an ejbql query an entity is retrieved without the related objects (lazy !)
2) The entity is detached for returning to a remote client. Not a Java client in this case.
3) The detached object is serialised by the server container for transport to the client.

The only solution is now to set all the relationships of the detached entity to NULL.

I think there should be a simple pattern for this case ?!?

Just a thought:
- use the access type "field" for those classes
- change the getter to return a new collection filled with the entries from the persistent collection
- change the setter to clear() the persistent Collection and add all entries from the given collection

That would prevent you to merge() serialized entities. All lazy collection would be nullified in DB

In the meantime I thought it's not a good idea anyway, because the Collection.addAll()-Method would iterate the (possibly lazy) persistent collection and result in a well known LazyInitializationException during serialization.

I did not quite understand, why it would break merge() but this is nearly OT.
;-)

I thought the (easy) detachment and returning of detached entities was part of the new EJB 3 specification, but I think this is not the case ?!?

It indeed is part of the spec and it actually works quite fine.
But Flex's special Serializer is not part of the EJB spec.

Maybe you can add custom serializer classes to Flex for the persistent collection types. I did that for an XML serializer (XStream) a while ago.

Good luck.