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From "Patrick Linskey (JIRA)" <j...@apache.org>
Subject [jira] Created: (OPENJPA-126) EntityManagers cannot be serialized
Date Wed, 07 Feb 2007 17:26:05 GMT
EntityManagers cannot be serialized
-----------------------------------

                 Key: OPENJPA-126
                 URL: https://issues.apache.org/jira/browse/OPENJPA-126
             Project: OpenJPA
          Issue Type: New Feature
          Components: kernel, jpa
            Reporter: Patrick Linskey


EntityManagers are not serializable or externalizable. This makes passivation of an EntityManager
a difficult task. We should investigate how to externalize an EntityManager in a meaningful
way. This could mean just writing out a stub that contains configuration information (potentially
even just the persistence unit name, or the Configuration's ID), or it could mean actually
serializing some or all of the local transactional cache to disk. The implications for the
functionality available after deserialization would differ depending on the approach taken.

I would like to see an implementation that efficiently wrote all the unflushed, dirty objects
to disk. This would probably be best implemented via a writeReplace() strategy, to avoid handling
all the transient fields in a Broker. Deserialization would then turn into a factory lookup
plus some sort of in-place reattachment of the deserialized unflushed instances.

Of course, if the entity instances themselves were not serializable, it would be difficult
to write them to disk. Theoretically, we could just write out the corresponding StateManagers,
and track the changed fields ourselves. I do not think that this is a good approach, however,
since it would cause the deserialized objects to lose any non-persistent state after deserialization.
I think that it is fair to require that instances be declared Serializable in order to use
this feature.

(We could optimize this a tad by detecting if an instance has only persistent fields, and
if so, do our own serialization work.)

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