Re: [hibernate-dev] What should happen to queued operations when a collection is detached?
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(a)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/c1934b72edb4f7815209376...