I'm trying to learn Hibernate core at the moment and I came across "JPA" (Java Persisitence API) lately and understand that it's available from the Java EE.

I would like to seek some clarification here.

1. It's called EJB3 JPA, so does it mean we have to implement EJB in our application in order to use this JPA thing?

2. Can this EJB3 JPA generate SQL to multiple dialect like Hibernate?

3. Is this JPA an alternative to Hibernate cos I read somewhere saying that it combines the best from a few of the OR mapping framework? If not, why?

4. Why should we use Hibernate as compared to this EJB3 JPA?

Please advise.
Thank you.

You can use JPA whereever you want.

You need to be more specific about what you mean by EJB (e.g. is it entitybeans, sessionbeans etc.) ...and in any case take a look at how
EJB3 before you choose not to use it ..it is so much better than EJB2



Hibernate EntityManager can.



hibernate has more features than JPA; but you can still use hibernate together with JPA getting standard API and then only in the case of something special use hibernate API.

Hi Max,

Sorry if my question below sounds weird, just trying to get the correct understanding based on some of things I read.

1. You mention we can use JPA whenever we want, does that mean we can use JPA without using Toplink or Hibernate?

2. When we say A is an "implementation" or "reference implementation", that means A is something that built on top of the JPA, such as Toplink Essential. Is there correct?

3. Do I understand correctly that JPA itself does not know how to generate to multiple database dialect SQL? It's the product such as Toplink or Hibernate that build on top of JPA that makes it able to generate SQL for various database dialect. And the type of support database dialect is again depends toplink or hibernate has to offer. Correct?

4. Toplink Essential is the reference implementation for EJB3 JPA (correct me if i'm wrong). So, for Hibernate side, is Hibernate EntityManager the same category of component as Toplink Essential?

5. Is "EJB3 JPA" different from "JPA"? Must we implement EJB if we want to use JPA?

Please advise.

You need *some* implementation of JPA, but it is not tied to an J2EE server.



no. It is not build *on top* of JPA it is an *implementation* of the JPA specification. Hibernate EntityManager and Toplink essentials is such things.



JPA is a *specification* not an *implementation* it does not care about what sql is generated, that is the *implementation*.



yes



same answer that before. What do you mean by "implement EJB" and have you looked at what EJB actually means in EJB3. In any case, if you by EJB mean: "am I required to use a full appserver" then no you don't.

And you don't need session beans (but they are definitly recommended), you just need entity beans (which is just POJO's in EJB3)

/max

Actually no, Hibernate EntityManager should be compared to the full featured Toplink. Toplink Essential is a subset of Toplink and can't compete against Hibernate EntityManager

Why is it named as "EJB3 JPA" and not just JPA?


To me, "EJB3 JPA" sounds like it's a "JPA for EJB3", but EJB3 itself is also a specification right? not something that implements JPA right? :P