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

[Gail Badner]

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> 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
> https://lists.jboss.org/mailman/listinfo/hibernate-dev
>