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From Rick Curtis <curti...@gmail.com>
Subject Re: Advice Requested: Instance Loading bug in 2.3.0
Date Sun, 04 May 2014 13:24:30 GMT
A couple quick thoughts/debug suggestions for you :

- Can we get a copy of your persistence.xml file?
- Can you try to run with 2.0.x to see if something was introduced in the
original 2.0 implementation effort, or if it came sometime after?
- Have you tried setting your fetch graph to be entirely loaded by the
default fetch group? I know this probably isn't ideal, but it might be an
interesting data point.

If you are able to trim the test down into something consumable by others,
I'd be interested in taking a look at it.

Good luck,
Rick


On Fri, May 2, 2014 at 5:43 PM, Jeff Oh <oh.jeff@gmail.com> wrote:

> Hello All,
>
> We've recently upgraded to 2.3.0 (from 1.2.2) and have encountered a nasty
> bug where when loading a complicated cyclic object graph using a fetch
> group, some relationships are not being populated under some circumstances.
>
> Unfortunately, the graph really is quite complicated, and while I have a
> set of test data where the problem can be reliably duplicated, I haven't
> been able to make an integration test do the same yet.  A simplified
> version of the graph is that A is 1:M to B and A is 1:M to C, B is M:1 to A
> (Bidirectional), and C is M:1 to A and C is also M:1 to B.  The net effect
> is a graph where cycles can exist, although in practice they generally
> don't other than the bidirectional relationship between A and B.
>
> Our failing case is interesting.  When we load single instances of B (call
> them B1 and B2) one at a time the load is always successful, with all of
> the A, B, and C relationships populated - but only if loaded one at a time.
>  In other words, if we run entityManager.find(B1) or
> entityManager.find(B2), then all is well.
>
> An ascii art version of the graph traversals might look something like
> this:
>
> B1 -> A1 -> C1    -> B3      -> A3     -> B3        -> A3
>                                                      -> B3-1     -> A3
>                                                      -> B3-2     -> A3
>               -> C1-2 -> ...
>                   ....
>
> B2 -> A2 -> C2    -> A3       -> B3       -> A3
>                                          -> B3-1    -> A3
>                                          -> B3-2    -> A3
>               -> C2-2 -> ....
>                    ...
>
> where B is M:1 to A, A is 1:M to C and A is 1:M to B.
>
> Interestingly, while B1 and B2 are separate objects, they do share several
> common objects in their graphs - call them A3 and B3 (as well as B3-1 and
> B3-2).  If we run a query that loads both B1 and B2 in the same query -
> entityManager.find(B1 + B2), then one of the relationships from one of the
> other B objects in the graph (call it B3) B3->A is null (not populated),
> where B3->A should == A3.  To clarify, B1.A1.C1.B3.getA() should equal A3,
> and instead is null, and B2.A2.C2.A3.B3.getA() should also equal A3, but
> instead is null.
>
> Of course, the graph is being detached after load, so unfortunately lazy
> loading the B3->A relationship is not possible.
>
> When running through a debugger, it looks like what happens is that the A3
> and B3-* instances are each being created more than one time.  This seems
> to make sense because the graph has cycles, relationships are loaded
> recursively, and instances are not added to the transactional cache
> (ManagedCache) until after they are fully initialized with all fields
> loaded.   Therefore new instances will not always be fully created when
> they are needed again.  As the call stack goes forward, the newest A and B
> instances get fully initialized with all fields loaded.  However, as the
> call stack unwinds, the oldest A and B instances are the ones that
> eventually win, and one of the B instances that wins is not fully
> initialized and has a null field in it's A relationship (e.g. B3.getA() is
> null, because B3's A was not ever set).
>
> I'm currently tracing this through to try and determine exactly why the
> outer (eldest) B3 isn't getting loaded with its A3, but while I do so, I
> was wondering if anyone else has encountered a similar problem or has any
> suggestions as to where I should focus my efforts.
>
> My current thinking is that the multiple loading issue is OK and expected,
> and that the problem is that the oldest B's aren't getting loaded with
> their A's.  But it is possible that the problem is that each individual
> entity should only be initialized once, and that this is the root issue.
>  Comments would be welcome.
>
>
> Thanks,
>
> Jeff
>



-- 
*Rick Curtis*

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