Hi;

I have two persistence units each representing two different schemas. These schemas have the same tables. The aim is to gather default entity values from the first persistence unit, and store the persistent entities on the second persistence unit. Here is how i try to mange this purpose:

EntityManagerFactory factory = Persistence.createEntityManagerFactory("firstpersistenceunit");
EntityManager em = factory.createEntityManager();
myEntity = em.find(MyEntity.class, 1);
em.close();
factory.close();
//myEntity.setId(0);
myentity.setName("bla bla");
EntityManagerFactory factory = Persistence.createEntityManagerFactory("secondpersistenceunit");
EntityManager em = factory.createEntityManager();
em.persist(myEntity);
em.close();
factory.close();

I can manage to persist the entity in the second schema, but if I uncomment the line setting the entity id as 0, I get the following error saying trying to persist a detached entity, which makes me confused. Why thus the object become detached when I set its id to 0 and can be persisted without any problem if I do not ?

That may have to do with the unsaved value for the persistence id of your object. The ejb 3 spec does not specify explicitly how a persistence manager differentiates a new/transient entity from a dettached one (may be provider specific), but hibernate does.

Look at the unsaved-value attribute of the id element:

http://www.hibernate.org/hib_docs/v3/reference/en/html/mapping.html#mapping-declaration-id

Indeed, entity managers are supposed to throw an exception when attempting to persist a dettached entity



So, when not setting the Id to 0, what is the value of this property right before persisting the entity through the second entity manager? Is it 1? null?

Hope this helps a little,

Regards,

The id is 1 at that time, since I assigned 1 to the id's of entities in the first persistence unit. The stranger thing is when I add an element to a collection (actually an ArrayList) of the entity (MyEntity), if I do not set its id as 0, then I get "PersistentObjectException: detached entity passed to persist" exception. So it seems I have to give a not null id to the root, and give 0 to ids to each children in order to persist each one. Although I could not get the idea behind...