Dain Sundstrom (who is a member of Geronimo project) did some
preliminary testing of Cayenne JPA provider in the OpenEJB container
last week - you've seen some jiras that he opened. I am taking
further discussion to the list (not sure if Dain is subscribed, so I
am cc'ying to him as well).
So the enhancer... I tried to run the OpenEJB JpaTest [1] with
Cayenne provider. It fails to enhance the Employee object [2], even
if it is explicitly mentioned in the PersistenceUnit, because it was
loaded in the JVM *before* Cayenne provider was started and
Provider.createContainerEntityManagerFactory(..) was called.
I was trying to think of ways to "fix" it, but considering that
java.lang.instrument.Instrumentation doesn't allow to enhance already
loaded classes ("redefineClasses" method places serious limitations
on what can be done, namely adding new fields is not allowed), looks
like JPA users will have to deal with specific startup order
requirements. In-container and Java SE operation modes will look
different:
1. In-container: provider shouldn't directly access its own agent,
and simply register a needed ClassTransformer with container-provided
PersistenceUnitInfo. Container on the other hand has the
responsibility to hook up PersistenceUnitInfo implementor to the
agent, and ensure that provider is started *before* and persistence
classes are loaded in the app class loader. So I wonder whether the
fact that JpaTest worked with OpenJPA provider by some coincidence?
2. Standalone: for the enhancer to work, an application must ensure a
call to Persistence.createEntityManagerFactory() prior to the entity
classes loaded in runtime. This sucks, and the only way around is to
run enhancer straight from the agent. I think that's what OpenJPA
does. Some time ago we decided [3] to avoid putting any Cayenne
runtime classes in the agent, but it looks like we don't have a
choice. Unless somebody can suggest a better way of providing
reliable runtime enhancement, I will change the behavior to provide a
"fat" agent.
[1] https://svn.apache.org/repos/asf/incubator/openejb/trunk/openejb3/
container/openejb-core/src/test/java/org/apache/openejb/core/cmp/jpa/
JpaTest.java
[2] https://svn.apache.org/repos/asf/incubator/openejb/trunk/openejb3/
container/openejb-core/src/test/java/org/apache/openejb/core/cmp/jpa/
Employee.java
[3] http://objectstyle.org/cayenne/lists/cayenne-devel/2006/08/0088.html
Andrus
P.S. Dain - are there any other show stopper issues in your testing
(except for no EJBQL)?
