Cloning JPA entity

Question

I have a JPA entity already persisted in the database.
I would like to have a copy of it (with a different id), with some fields modified.

What is the easiest wa

Answer 1

I face the same problem today : I have an entity in database and I want to :

• get it from database
• change one of its attributes value
• create a clone of it
• modify just some few attributes of the clone
• persist clone in database

I succeed in doing following steps :

@PersistenceContext(unitName = "...")
private EntityManager entityManager;

public void findUpdateCloneAndModify(int myEntityId) {
  // retrieve entity from database
  MyEntity myEntity = entityManager.find(MyEntity.class, myEntityId);
  // modify the entity
  myEntity.setAnAttribute(newValue);
  // update modification in database
  myEntity = entityManager.merge(myEntity);
  // detach entity to use it as a new entity (clone)
  entityManager.detach(myEntity);
  myEntity.setId(0);
  // modify detached entity
  myEntity.setAnotherAttribute(otherValue);
  // persist modified clone in database
  myEntity = entityManager.merge(myEntity);
}

Remark : last step (clone persistence) does not work if I use 'persist' instead of 'merge', even if I note in debug mode that clone id has been changed after 'persist' command !

The problem I still face is that my first entity has not been modified before I detach it.