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https://issues.apache.org/jira/browse/OPENJPA-1163?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12733960#action_12733960
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Michael Dick commented on OPENJPA-1163:
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Hi Ravi,
This patch demonstrates a race condition more than anything else. You have two
transactions. Tran 1 gets a copy of the entity, removes everything from its
collection, then adds ten more items. Tran 2 gets a copy of the entity and just
adds ten items. To show this just print out the size of newA.getAItems() before
committing tran 1.
In Tran 1 the entity has only 10 items , in tran 2 the entity has 20. The last
one to commit wins. It's a unidirectional relationship - I'm guessing this is
because it's a uni-directional relationship and A is the owner (even though the
updates are in the AItem table) and therefore the state in A trumps the state
in AItem.
Interestingly enough if you updated any field in A you should see an
OptimisticLockException which would explain the problem better.
> Data consistency issues while modifying collections.
> ----------------------------------------------------
>
> Key: OPENJPA-1163
> URL: https://issues.apache.org/jira/browse/OPENJPA-1163
> Project: OpenJPA
> Issue Type: Bug
> Components: kernel
> Affects Versions: 2.0.0
> Environment: openJPA trunk. Derby DB.
> Reporter: Ravi P Palacherla
> Assignee: Ravi P Palacherla
> Fix For: 2.0.0
>
> Attachments: OPENJPA-1163_trunk.patch
>
>
> There are data consistency issues when modifying more number of elements in a
> collection Vs less number of elements.
> Following is a detailed explanation about the issue with example:
>
> - Entity A has a collection of Entities AItems with cascade ALL.
> - Test case :
> Clear all the data inside tables representing Entity A and AItems.
> Create 3 entity managers em1,em2 and em3.
>
> em1.begin()
> create A on em1 with id "1"
> add 10 elements of AItems (id's from 0-9) to the created A(id 1).
> persist A.
> em1.commit()
>
> em1.begin()
> merge A ( created in the previous step)
> Remove 3 elements of AItems from the merged A.
> Add 3 elements of AItems ( id's 10,11,12) to the merged A (id 1).
>
> With out committing em1
>
> em2.begin()
> query database to fetch A and construct object result2 of entity A.
> Add 3 elements of AItems ( id's 13,14,15) to fetched A ( result2)
> em2.commit ()
> em1.commit()
>
> em3.begin()
> query database to check the size of AItems that are related to A ( id 1)
> em3.commit()
>
> The result on em3's query for AItems related to A, returns 13 as expected.
> 13 ( Initial 10 - em1's 3 + em1's 3 + em2's 3).
>
> When the same test case is repeated with removing and adding 10 elements
> instead of 3 as before then I get wrong results.
>
> Add initial 10 AItems (id's 0-9) for A.
> commit()
>
> em1 will remove 10 AItems from the collection of A.
> em1 will add 10 AItems (id's 10-19) to collection of A.
>
> em2 will add 10 AItems (id's 20-29) to collection of A.
>
> Commit em2.
> Commit em1.
>
> Then instead of 20 elements ( Initial 10 - em1's 10 + em1's 10 + em2's
> 10), I see only 10 elements.
>
> The 10 elements that I see are from em1's added AItems ( id's 10-19).
> I think the cause of the issue is that, when more number of elements
> (compared to initial element count of collection) in a collection are
> modified then collection tracking is disabled and openJPA tries to do the
> following:
> -- Delete every thing from the collection
> -- Insert data back to collection.
> While Inserting the data back it does not consider adding the dirty records (
> em2's 10 added elements ) because the collection tracking is disabled.
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