Re: Can I reuse instances?

[Craig L Russell]

Hi Dain,






Craig

On Apr 8, 2007, at 1:15 PM, Dain Sundstrom wrote:

I haven't looked in detail at the life cycle of CMP beans in a couple of years, but in general you can't simply keep the state of the underlying Entities through the life cycle. CMP beans are pooled and reused in transaction contexts and you have to load the state at specific points in the life cycle. Using the primary key stored in the CMP bean to do em.find at the appropriate time is the obvious way to take advantage of the em second level cache. To the extent that this is not efficient, we should fix it in the JPA layer not the CMP layer.

Thanks for the great info Patrick.





1) Beans are created and the ejb context is set into them
2) A primary key is assigned
3) Data is loaded into the bean





Thanks for help,

-dain

On Apr 8, 2007, at 8:56 AM, Patrick Linskey wrote:

For now, I'm going to leave my implementation the way it is, without instance reuse, and wait until someone complains loudly. BTW in CMP there are a several places in the lifecycle of entities that people like to reuse beans... People like to reuse instances at all three levels. The solution you suggest below addresses the first. Would it be possible to hook the cache to give the OpenJPA system an entity with data already loaded? Anyway, for not I'm just going to wait and see if anyone deeply cares about this feature.

Hi,

The easy way to do this is with extended persistence contexts. In an

duration of the entity manager, not the transaction.


the container creates an EM proxy that gets injected / looked up, and
that internally delegates through to the "right" EM internally. (I'm
assuming that you're doing this for your EJB2 container work.)



This would be closer to spec-compliant behavior, but wouldn't be 100%
there.


factory for creation of new instances. This would require creating an

and changing the nine places in code that use that method directly to
call the factory instead.


be that hard. Note that you wouldn't want to use an

on.


other alternates as well, such as creating clones or something of the
sort.

Out of curiosity, what is slow about creating your instances?

-Patrick

--
Patrick Linskey
BEA Systems, Inc.


by email and then delete it.

extended persistence context, your working set of objects lasts for the In a JTA environment, the container is supposed to set things up so that EMs are transactional by default. To the best of my knowledge, between this rule and the persistence context propagation rule, this means that So, going with an extended PC is probably not sufficient for you, if you want to be spec-compliant. One thing that you could do, though, is make your EM proxy smart about holding onto a single EM for a long amount of time for use in transactions, but only use that EM during transactions. The 100% solution would be to change OpenJPA to delegate to a pluggable interface with the two pcNewInstance() signatures in PersistenceCapable, Then, you could plug in whatever instance pooling logic you prefer, and you'd be in good shape. You'd need to figure out some way to know when to re-pool the instances, but in a container environment, that shouldn't Synchronization.afterCompletion() callback, since if it's detached, the instance might be used after completion in a rendering step or something of the sort, or it might be tucked away in session state for use later Of course, if you've got a pluggable instance factory, you'd have some _____________________________________________________________________ __ Notice: This email message, together with any attachments, may contain information of BEA Systems, Inc., its subsidiaries and affiliated entities, that may be confidential, proprietary, copyrighted and/or legally privileged, and is intended solely for the use of the individual or entity named in this message. If you are not the intended recipient, and have received this message in error, please immediately return this

-----Original Message-----
From: Dain Sundstrom [mailto:[EMAIL PROTECTED]
Sent: Sunday, April 08, 2007 12:18 AM
To: open-jpa-dev@incubator.apache.org
Subject: Can I reuse instances?

Is it possible to reuse instances from transaction to transaction?

I would like to be able to create a bean in one transaction, detach
it and reattach the same instance in a new transaction.  My
goal here
is specifically to reuse instances across transactions because they
have a very expensive creation cost, and no I can not redesign the
system.

I tried a quick test case using merge, but merge returned a new
instance:

         beginTx();
         Employee dain = entityManager.find(Employee.class, dainPk);
         assertEquals(dain.getFirstName(), "Dain");
         commitTx();

         beginTx();
         assertSame(dain, entityManager.merge(dain));
         assertEquals(david.getFirstName(), "Dain");
         commitTx();

When I try to use the refresh method, OpenJPA complains that the
entity "is not managed by this context".

So is there anyway for me to reuse instances?

-dain

Notice: This email message, together with any attachments, may contain information of BEA Systems, Inc., its subsidiaries and affiliated entities, that may be confidential, proprietary, copyrighted and/or legally privileged, and is intended solely for the use of the individual or entity named in this message. If you are not the intended recipient, and have received this message in error, please immediately return this by email and then delete it.

Craig Russell
Architect, Sun Java Enterprise System http://java.sun.com/products/jdo
408 276-5638 mailto:[EMAIL PROTECTED]
P.S. A good JDO? O, Gasp!

smime.p7s
Description: S/MIME cryptographic signature