EJB3/JPA Entended Persistence Context and merge()

smithbstl · **Joined:** Fri Jul 28, 2006 12:01 pm **Posts:** 21

This is kind of a general question but...
Is there ever a need to merge an entity when using an Extended Persistence Context? I guess the overarching question is do entities ever become detached in an extended pc? Being new to EJB3/JPA I am having trouble conceptualizing when to use persist() vs using merge(). I know that persist is usually thought of as an sql INSERT and merge is usually thought of as an sql UPDATE but does merge() ever call an INSERT when creating a new entity? Are merge() and persist() interchangeable when dealing with new entities (or are they ever interchangeable)?

Thanks for any help.

-Brian

emmanuel · **Posted:** Mon May 14, 2007 1:42 pm

you can use merge instead of persist to make a transient entity persistent

Code:

Entity persistentE = em.merge(e);

persist is probably going to be more efficient though

you cannot persist() a detached object, so the 2 operations are not interchangeable.

An EPC is useful whithin a user conversation, if you want to reattach object in between different conversations, then merge makes sense even in an XPC.