javax.persistence.Entitymanager: remove() method

Question

Does remove(Object entity) method of EntityManager work only on those objects got from find() method?

I have following code snippet:

Answer 1

Something to that direction. EntityManager.remove works only for managed entities. How you obtained these managed entities does not matter, it can be for example:

• via JPQL query
• via Criteria API query
• find method in EntityManager
• by following relationship from some other entity.
• created new entity and persisted it

But simply creating new object and trying to remove it does not work, because this new object is not managed entity. Also entity should not be yet detached.

Life of entity is quite much as follows, all in same transaction (entities outside their transaction are not managed):

Entity ent = new Entity(1); //entity is in new state, EntityManager never know
                            //anything about it
em.persist(ent); //entity is managed as long as not disconnected 
                 //from EntityManager
em.clear(); // all previously managed entities, including ent, are now detached

Entity same = em.find(1); //managed same
em.remove(same); // entity is removed