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https://issues.apache.org/jira/browse/OPENJPA-894?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Michael Dick updated OPENJPA-894:
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Attachment: OPENJPA-894-scrollable-1.0.x.patch.txt
The idea of manually adding in the duplicates made me a little nervous. I've
attached an alternate approach which uses scrollable result sets if we detect a
left join fetch (as indicated by the presence of joins in the fetch plan).
When a Left Join Fetch is used we'll process the resultSet as we normally do,
but rewind back to the original position after processing the eager results.
The changes should only affect LJF queries which might see a slight drop in
performance for using scrollable result sets.
> LEFT JOIN FETCH queries with fresh fetches from the db do not follow JPA Spec
> 4.4.5.3
> -------------------------------------------------------------------------------------
>
> Key: OPENJPA-894
> URL: https://issues.apache.org/jira/browse/OPENJPA-894
> Project: OpenJPA
> Issue Type: Bug
> Components: query
> Affects Versions: 1.2.0
> Environment: Any, tested with Windows
> Reporter: Jody Grassel
> Attachments: FetchJoinTest.zip,
> OPENJPA-894-scrollable-1.0.x.patch.txt, OPENJPA-894.patch
>
>
> Discovered what seems to be a break with JPA Specification 1.0, section
> 4.4.5.3 (Fetch Joins). The query in question uses the LEFT JOIN FETCH
> sematic, so there is the expectation that the result list will contain a copy
> of the entity reference for every match on the right side of the join (the
> spec uses the example with the query "SELECT d FROM department d LEFT JOIN
> FETCH d.employees WHERE d.deptno = 1" where 5 employees are members of
> department(pk=1) the resultlist should have 5 copies of Department(pk=1). )
> Now, if I create all of the entities, persist them to the database, but do
> not clear the persistence context (leaving all the new entities managed by
> the persistence context still), the query performs as expected. I get
> multiple copies of the entity I issued the query for, one for each item
> successfully matching the LEFT JOIN FETCH. In the example I will update
> shortly, I get:
> [junit] --------------------------------------------------
> [junit] Executing testQuery001
> [junit] Executing named query getAGroup with intData=42 ...
> [junit] ResultList size: 8
> [junit] 1 EntityA(id=1): 42, Entity A - PK 1
> [junit] 1 EntityA(id=1): 42, Entity A - PK 1
> [junit] 1 EntityA(id=1): 42, Entity A - PK 1
> [junit] 1 EntityA(id=1): 42, Entity A - PK 1
> [junit] 1 EntityA(id=2): 42, Entity A - PK 2
> [junit] 1 EntityA(id=2): 42, Entity A - PK 2
> [junit] 1 EntityA(id=2): 42, Entity A - PK 2
> [junit] 1 EntityA(id=2): 42, Entity A - PK 2
> However, if I clear the persistence context, forcing OpenJPA to make a fetch
> from the database, I only get unique instances of the entity I issued the
> query for, not multiple copies for each match on the right side of the join.
> [junit] --------------------------------------------------
> [junit] Executing testQuery002
> [junit] Clearing persistence context...
> [junit] Executing named query getAGroup with intData=42 ...
> [junit] ResultList size: 2
> [junit] 1 EntityA(id=1): 42, Entity A - PK 1
> [junit] 1 EntityA(id=2): 42, Entity A - PK 2
> Both tests use the exact same code for everything, except testQuery002 does a
> em.clear() before running the query.
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