merging a detached or new entity with an existing entity in hibernate/jpa best practice question

Question

When the business layer creates a new entity, which logically represents an instance of an existing entity that should be updated (say they share the same business key), is

Answer 1

If your entity is a detached entity the only thing u really need to do is to invoke entityManager.merge(user). You dont need to exec any finder method. If your entity is not detached but rather new (it does not have id specified) you should find appropriate entity in the database prior performing any modification operations on that entity and merge it afterwards. i.e:

User user = userDao.findBySomething(Criteria c);

//stuff that modifies user 

user = userDao.merge(user);