[hibernate-dev] What should happen to queued operations when a collection is detached?

[andrea boriero]

I would say to log a warning when the entity is detached and then clear the
queued operations.

On Fri, 5 Oct 2018 at 07:25, Gail Badner <gbadner at redhat.com> wrote:

>  Guillaume has reviewed my PR and I've pushed the fix to master.
>
> I still think the inconsistency should be resolved. I have no plans to do
> any more on this without any feedback.
>
> Regards,
> Gail
>
> On Tue, Oct 2, 2018 at 6:16 PM Gail Badner <gbadner at redhat.com> wrote:
>
> > Since I haven't heard anything back, I've gone ahead and updated my PR
> [1]
> > to ignore queued operations when merging a detached collection. This
> restores
> > the functionality that was in place prior to HHH-5855 (which caused
> > HHH-11209).
> >
> > In addition I've added warnings for the following situations:
> > * a detached collection is being merged that has queued operations;
> > * a collection with queued operations is attached to a session;
> > * a collection with queued operations is detached from a session.
> >
> > I've also added a test case that shows that Session#merge and
> > Session#saveOrUpdate have different results when called on an entity
> with a
> > collection with queued operations. When Session#merge is called, the
> queued
> > operations are ignored. When Session#saveOrUpdate is called, the queued
> > operations are executed on flush.
> >
> > I don't like this inconsistency, but I'm not sure what to do about it. I
> > don't think it's a good idea to have collections floating around with
> > queued operations. As far as the application knows, it is just an
> > uninitialized collection. I can see that the entity could find its way
> into
> > a new session, with surprising results.
> >
> > IIUC, an application probably shouldn't detach an entity with a
> collection
> > in this state (having queued operations), so I think it makes sense that
> a
> > warning be logged when this happens. On the other hand, the warning will
> > also be logged if a transaction involving updates to a collection with
> > queued operations fails.
> >
> > I would really appreciate some feedback on this, since HHH-11209 is a bad
> > regression that really should be fixed.
> >
> > Thanks,
> > Gail
> >
> > [1] https://github.com/hibernate/hibernate-orm/pull/2460
> >
> > On Fri, Sep 28, 2018 at 6:27 PM Gail Badner <gbadner at redhat.com> wrote:
> >
> >> HHH-11209 involves a bug merging a detached entity with an uninitialized
> >> collection that has queued operations.
> >>
> >> After looking into this issue I found a bug
> >> where AbstractPersistentCollection#operationQueue was not being cleared
> >> after a commit, if there was no cascade mapped for the collection.
> >>
> >> I've fixed that in a PR. [1]
> >>
> >> After that fix, the detached entity in the test case attached to
> >> HHH-11209 has an uninitialized entity without any queued operations
> after
> >> commit, which can be merged successfully in a new session/transaction.
> >>
> >> There is still a problem when Hibernate tries to merge a detached entity
> >> has an uninitialized collection with queued operations though. My PR
> throws
> >> UnsupportedOperationException in this case, and there is a test case
> that
> >> reproduces it.
> >>
> >> I've been working on a fix to add support for this, but I have my doubts
> >> that it really should be supported. I see that prior to fixing HHH-5855
> >> (which caused HHH-11209), Hibernate simply ignored the queued
> operations in
> >> the detached collection. [2].
> >>
> >> The fix for HHH-5855 properly dealt with merging a managed collection
> >> that was uninitialized with queued operations. It introduced the bug
> where
> >> a NullPointerException would get thrown if that collection  was
> detached.
> >>
> >> If we want to support merging the queued operations, then I would
> >> consider that an improvement. Would this be a worthwhile improvement?
> I'm
> >> guessing not, but I wanted to get some opinions.
> >>
> >> For now, I see a couple of ways to deal with this so that HHH-11209 can
> >> be wrapped up:
> >> 1) ignore queued operations in a detached collection when merging, as
> was
> >> done before HHH-5855 was fixed.
> >> 2) clear the queued operations when the collection is detached.
> >>
> >> Comments?
> >>
> >> Thanks,
> >> Gail
> >>
> >> [1] https://github.com/hibernate/hibernate-orm/pull/2460
> >> [2]
> >>
> https://github.com/hibernate/hibernate-orm/commit/c1934b72edb4f781520937618b3b750bebb84576#diff-2c7912a47063b9ea81323bf9c6628895L651
> >>
> >
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