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https://issues.apache.org/jira/browse/OPENJPA-2405?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13695643#comment-13695643
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Jody Grassel commented on OPENJPA-2405:
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Just reviewing this JIRA and wanted to post my own thoughts. First, some clips
from the JPA Specification that I think are relevant:
3.2 Entity Instance’s Life Cycle
This section describes the EntityManager operations for managing an entity
instance’s lifecycle. An entity instance can be characterized as being new,
managed, detached, or removed.
• • • •
A new entity instance has no persistent identity, and is not yet associated
with a persistence context.
A managed entity instance is an instance with a persistent identity that is
currently associated with a persistence context.
A detached entity instance is an instance with a persistent identity that is
not (or no longer) associated with a persistence context.
A removed entity instance is an instance with a persistent identity, associated
with a persistence context, that will be removed from the database upon
transaction commit.
-- What I take from this is that an Entity Class that has been freshly created
by its constructor (ie, not created by em.find() or a JPA query) and has never,
ever been touched by an em.persist() or em.merge() operation is a "new entity".
Such an object will not have any StateManager (DetachedStateManager or
otherwise, it is simply null) associated with its internal state (internal
state being the hidden variables added by enhancement.)
-- A "managed entity" is an Entity Class instance that has a link to a live
StateManager in its internal state -- and there's caveats to that. A
StateManager is associated to one and only one Persistence Context (ie,
EntityManager instance) - to those and only those Persistence Contexts is the
entity a "managed entity". A new entity becomes a managed entity when
em.persist() or em.merge() is called on it. (Managed entities are also
provided by find/query operations (though it would return a detached entity if
it's a CMTS entitymanager invocation outside of a transaction.))
-- To any other Persistence Context, because it is not "new" (because it has a
StateManager object associated with it) and has a non DetachedStateManager that
is associated with another Persistence Context, it should be interpreted as a
"detached entity" (even if the StateManager associated with the Entity Object
instance's internal state is not a DetachedStateManager.) So calling
em.merge(entityWithSomeOtherPCsStateManager) should be treated as a detached
entity, and return a new Entity Object instance. Which could create
"interesting problems" if the original entity doesn't have a committed row on
the database yet (because the two different PCs will have two different db
connections, and a merge operation will trigger a fetch operation from the
database/cache.) Remember the JPA spec requires Read-Committed to be the
minimum isolation level.
> EntityManager.merge does not work for entity that is managed by another
> EntityManager
> -------------------------------------------------------------------------------------
>
> Key: OPENJPA-2405
> URL: https://issues.apache.org/jira/browse/OPENJPA-2405
> Project: OpenJPA
> Issue Type: Bug
> Affects Versions: 2.2.3
> Reporter: Arne Limburg
> Attachments: OPENJPA-2405.patch
>
>
> EntityManager.merge does not work for entity that is managed by another
> EntityManager. Instead of updating that entity OpenJPA tries to persist the
> entity a second time
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