Hi, Martin
Some replies in inline...
On 11/22/06, Martin Bayly <mbayly_at_telus.net> wrote:
>
> What is the relationship between the Oracle TopLink implementation and
> the TopLink essentials that was donated to Glassfish?
I'm not Oracle guy, but as far I know commercial TopLink has more
functionalities such as distributed 2nd-level cache, query cache, tools,
non-RDB mappings, etc. Whereas TopLink Essentials is just focusing on JPA
implementation.
Or put another way, are features like the SoftCacheWeakIdentityMap
> described in the TopLink Cache Concepts documentation also available
> within the Glassfish implementation (presumably with vendor specific
> configurations)?
Yes, please see below.
http://www.oracle.com/technology/products/ias/toplink/jpa/resources/toplink-jpa-extensions.html
The background to this whole question is the ongoing debate about the
> best way to use ORM solutions like JPA/TopLink/Hibernate in a single
> tier rich client application - usually single user database.
>
> Some people believe a single application level session/entity
> manager/persistence context is the best approach as it simplifies having
> long lived domain objects attached to user interface controls.
>
> However, this proved to be inappropriate with Hibernate as the Hibernate
> Session would just keep growing unless you specifically evicted objects
> that were no longer referenced by the UI which can be hard to track.
>
> So the alternative is to use a session/entity manager per interaction
> which means you have to be able to reattach detached objects and you may
> end up with multiple references to the same object if you are not
> careful (with Hibernate you also have to be careful about lazy loading
> outside the session - though apparently not with TopLink).
>
> How does the Glassfish implementation handle objects in the persistence
> context? If you open an EntityManager session, will TopLink essentials
> hold onto any objects loaded into that persistence context until the
> EntityManager is closed, or is it possible to set it up with a weak
> reference identity mapping, so that if the application no longer holds a
> reference to these objects, they will be candidates for GC?
Weak type cache settings are applied only to 2nd-level cache but not to
persistence contexts. The persistence context should be maintained until it
is cleared or closed according to JPA spec. I think you'd better maintain
persistence contexts per transaction like Java EE(container-managed)
transaction-scoped EntityManager.
Thanks,
-Wonseok
Cheers
> Martin
>