Am 29.05.2012 06:49, schrieb Balázs Zsoldos:
* Shall import-package used for a bundle that has OpenJPA compile time
enhancement?
For the model classes, or for the additional package dependencies added
by the enhancer? If the framework supports weaving hooks, the additional
dependencies should be added automagically.
* If an Entity class is enhanced by OpenJPA, can it be used in
multiple Persistence Units?
Are you trying to follow the OSGi Enterprise JPA spec, or just rolling
your own OSGi + JPA environment? The spec requires all model classes of
a persistence unit to be in the same persistence bundle.
I tried using entity classes from multiple bundles with OpenJPA, which
may or may not work, depending on the context. For some join queries
containing more than one class name, I sometimes had classloader errors.
* A class enhanced by OpenJPA can be used with other technologies like
Hibernate?
OpenJPA bytecode enhancement creates a compile-time and run-time
dependency of the enhanced bytecode on OpenJPA. I.e. you cannot compile
MyDAO.java on top of mymodel.jar containing your enhanced entity model
without OpenJPA on the classpath.
* An enhanced class needs OpenJPA present in the runtime even if we
use it with a different provider like Hibernate or EclipseLink?
Practically if import-package is necessary, could it be optional?
Hmm, never tried that. But even if Hibernate or Eclipselink could deal
with or ignore the enhanced bytecode, I suspect some other services
might get confused by two persistence providers in the system.
If anybody knows the answer to these questions please let me know! I
think I will have to read a bit about the enhancement of OpenJPA what it
does exactly and how it does it.
OSGi + JPA can be rather frustrating because whichever way you turn,
some bits and pieces are missing:
- Hibernate has no OSGi support at all.
- Both Hibernate and Eclipselink have too many serious bugs in core JPA
functions, which is why I favour OpenJPA, in spite of other peculiarities.
- OpenJPA compile-time enhancement is a major nuisance and breaks
compatibility with other persistence providers (my ceterum censeo with
OpenJPA...)
- Load-time weaving is great, OpenJPA supports it, but not all
containers do. It works fine with GlassFish 3.1 (with plain old WARs,
but probably not in OSGI mode, never tried.)
- About a year ago, I had a working demo with Equinox 3.7-SNAPSHOT +
OpenJPA 2.1 + Aries 0.4-SNAPSHOT using load-time weaving. The problem
with Aries is they seem to be too busy coding to release anything.
The latest Aries JPA release 0.3 of Jan 2011(!) does not support load
time weaving. Last time I tried, the trunk didn't even build, and the
new version-per-module approach adds to the confusion.
- I also tried Eclipse Gemini at about the same time and dismissed it
because it forces explicit Spring package dependencies on your
application bundles, which really should be an implementation detail of
the container.
You can find some sample code, both with Aries and Gemini, here:
http://code.google.com/p/osgi-enterprise/
Some background on Aries + OpenJPA setup is in this blog:
http://hwellmann.blogspot.de/2010/09/openjpa-and-osgi.html
Regards,
Harald
