[hibernate-dev] Relations are not loaded when using Fetch Profiles

[Vladimir Martinek]

HHH-10745, runnable test case attached to that issue 
(org.hibernate.test.fetchprofiles.cycle.tar.gz).

Thank you

Vladimir



On 06/07/2016 06:00 AM, Gail Badner wrote:
> Please create a Jira issue and attach a runnable test case.
> Thanks,
> Gail
>
> On Thu, Jun 2, 2016 at 5:45 AM, Vladimir Martinek <vm at sykora.cz 
> <mailto:vm at sykora.cz>> wrote:
>
>     Fetch profiles fail to load certain relations because of invalid cycle
>     detection in MetamodelGraphWalker. Below is an example.
>
>     I have compared the behaviour of Fetch Profiles and standard EAGER
>     relations (EAGER does not suffer from this problem). The
>     MetamodelGraphWalker graph walker produces the same results, the
>     SQL is
>     the same (missing relation).
>
>     With EAGER the relation is loaded in second pass, via
>     SessionImpl.internalLoad(). There it is decided what LoadType is
>     used -
>     for eager it uses INTERNAL_LOAD_EAGER, for lazy INTERNAL_LOAD_LAZY. It
>     does not take into account the fetch profiles here!
>
>     The last place I can get hold of fetch profiles in in
>     AbstractLoadPlanBasedEntityLoader line 82. After that the fetch
>     profile
>     information is lost, never making it anywhere near to
>     SessionImpl.internalLoad().
>
>     I would like to implement this, but to do that, I need someone to
>     point
>     me in the right direction. Most of all I need answers to following
>     questions:
>
>     1) Is it right to assume the fetch profiles should be evaluated in
>     SessionImpl.internalLoad() and appropriate LoadType used when
>     detected a
>     relation affected by a fetch profile?
>     2) If so, what is the intended way of getting the fetch profile
>     information to SessionImpl.internalLoad()?
>
>     Also, a colleague of mine attempted to implement FetchType.SELECT
>     fetch
>     strategy and ended up with precisely the same problem. I believe
>     solving
>     my issue would pave way for quick FetchType.SELECT implementation
>     (which
>     we could also use on our project).
>
>
>     Thank you
>
>     Vladimir Martinek
>
>
>     Example:
>
>     Have 5 entities - Start, Via1, Via2, Mid and Finish with following
>     relations (all LAZY):
>
>     Start n:1 Via1 n:1 Mid n:1 Finish
>     Start n:1 Via2 n:1 Mid n:1 Finish
>
>     Now, trying to use Fetch Profiles to load Start entity and all of its
>     relations. I would expect Hibernate to execute following SQL select:
>
>     SELECT * FROM Start s
>     LEFT OUTER JOIN Via1 v1 (path Start-Via1)
>     LEFT OUTER JOIN Mid
>     JOIN Finish
>
>     LEFT OUTER JOIN Via2 (path Start-Via2)
>     LEFT OUTER JOIN Mid
>     JOIN Finish
>
>     Unfortunately, ii ompletely omits the second join from Mid to Finish,
>     what I am getting is:
>
>     SELECT * FROM Start s
>     LEFT OUTER JOIN Via1 v1 (path Start-Via1)
>     LEFT OUTER JOIN Mid
>     JOIN Finish
>
>     LEFT OUTER JOIN Via2 (path Start-Via2)
>     LEFT OUTER JOIN Mid
>
>     I dug deeper into this and found cycle detection in
>     MetamodelGraphWalker, line 144. Basically, when MetamodelGraphWalker
>     detects a relation that has already been visited, it considers it a
>     cycle. But in my case it is not a cycle - I just came to the same
>     relation twice using two different paths.
>
>
>     _______________________________________________
>     hibernate-dev mailing list
>     hibernate-dev at lists.jboss.org <mailto:hibernate-dev at lists.jboss.org>
>     https://lists.jboss.org/mailman/listinfo/hibernate-dev
>
>


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