Hello JDO team,
I just came back from holidays and it seems I'm too late as you already
voted. But still, I'd like to mention an issue about the feature
detachOnCommit: When using a JDO implementation within a J2EE server,
this feature IMHO doesn't make much sense, because the transaction might
be committed/rolled back later than the object needs to be detached.
This is especially true when using XA transactions. Additionally, it is
possible (at least some JDO implementations support it) to read data
without having any transaction (i.e. non-transactional read).
In both cases, it would be necessary to have additionally a
detachOnClose feature. Means, whatever happens first (commit transaction
or close persistence manager) should cause the objects to be detached.
To make things clearer, I'd like to shortly explain the handling
difference between non-J2EE and J2EE: When using JDO outside a managed
environment, the workflow works like this:
1. open the persistence manager
2. open a transaction
3. work with JDO objects
4. commit/rollback the transaction
5. close the persistence manager
All the above steps are performed explicitely by the programmer.
Within a J2EE container (i.e. within an EJB method), things are different:
1. J2EE opens a transaction for you _implicitely_ (the transaction
might involve many servers; thus it might already exist before the
EJB method is triggered)
2. obtain a persistence manager
3. work with JDO objects
4. close the persistence manager
5. J2EE commits/rolls back the transaction _implicitely_
A JDO object will be sent to the client using native serialization
either between 4 and 5 (with XA transactions) or after 5 - though I'm
not completely sure, it might be always between 4 and 5 even with local
transactions.
JPOX fortunately already supports detachOnClose as a vendor extension,
but IMHO this feature deserves to be integrated into the JDO standard.
Best regards, Marco :-)
--
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Marco Schulze NightLabs GmbH
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