[ovirt-devel] hibernate's internal PersistentBag sent to FE

[Alexander Wels]

On Monday, June 01, 2015 10:51:28 AM Martin Perina wrote:
> ----- Original Message -----
> 
> > From: "Alexander Wels" <awels at redhat.com>
> > To: "Tomas Jelinek" <tjelinek at redhat.com>
> > Cc: "Liran Zelkha" <lzelkha at redhat.com>, devel at ovirt.org
> > Sent: Monday, June 1, 2015 4:19:47 PM
> > Subject: Re: [ovirt-devel] hibernate's internal PersistentBag sent to FE
> > 
> > On Monday, June 01, 2015 09:33:07 AM Tomas Jelinek wrote:
> > > ----- Original Message -----
> > > 
> > > > From: "Alexander Wels" <awels at redhat.com>
> > > > To: devel at ovirt.org
> > > > Cc: "Tomas Jelinek" <tjelinek at redhat.com>, "Liran Zelkha"
> > > > <lzelkha at redhat.com> Sent: Monday, June 1, 2015 3:16:34 PM
> > > > Subject: Re: [ovirt-devel] hibernate's internal PersistentBag sent to
> > > > FE
> > > > 
> > > > On Monday, June 01, 2015 09:08:50 AM Tomas Jelinek wrote:
> > > > > Hey all,
> > > > > 
> > > > > since the org.ovirt.engine.core.common.job.Job/Step... has been
> > > > > moved
> > > > > to
> > > > > use
> > > > > the JPA we have a problem on frontend. The problem is that the
> > > > > @OneToMany
> > > > > annotations results in a List which is of type PersistentBag. When
> > > > > we
> > > > > send
> > > > > this to Frontend it fails during deserialization. It actually fails
> > > > > quite
> > > > > bad because the FE already has an ui-override of it which is not
> > > > > correct
> > > > > resulting in a ton of NPEs in development mode.
> > > > > 
> > > > > So, there are 2 nasty fixes I have made where none of them should be
> > > > > merged
> > > > > but demonstrate the possibilities: 1: extend the FE to be able to
> > > > > work
> > > > > with
> > > > > the PersistentBag (https://gerrit.ovirt.org/#/c/41682/) not really
> > > > > good
> > > > > solution since the PersistenBag is an internal Hibernate class which
> > > > > is
> > > > > really not meant to be passed around
> > > > > 
> > > > > 2: fix on the backend to not send the PersistentBag but an
> > > > > ArrayList.
> > > > > This
> > > > > is only a PoC fixed on a command we face the problem
> > > > > (https://gerrit.ovirt.org/#/c/41797/) Obviously this is not going to
> > > > > work
> > > > > for other commands accessing the same Job nor for other entities.
> > > > > 
> > > > > So, the first option is generic but very very bad. The second option
> > > > > should
> > > > > be used but not sure how to do this in a cheep way (e.g. without
> > > > > using
> > > > > reflection to deep traverse everything sent back to frontend
> > > > > checking
> > > > > if
> > > > > it
> > > > > does not have a PersistentBag in it.
> > > > 
> > > > Tomas,
> > > > 
> > > > Thanks, I was investigating the same issue, I noticed it last Friday
> > > > just
> > > > before leaving, so I was investigating the problem to see what was
> > > > going
> > > > on. You are right we should not be sending PersistentBag to the
> > > > frontend
> > > > at all. So how about we do a combination of [1] and [2], but instead
> > > > of
> > > > delegating in [1] we actually simple throw an exception stating don't
> > > > sent PersistentBag to the front end. that way anyone inadvertently
> > > > using
> > > > it will be notified immediately (since their code won't work).
> > > 
> > > Throwing the exception would help us in debugging but the main question
> > > is
> > > how will we make it work? Since we are planning to move more and more to
> > > JPA so we will face this issue more and more often. Solving it one by
> > > one
> > > on backend in each command is not going to work.
> > 
> > How about something like this [1]? It appears to use some aspects to
> > translate
> > the hibernate internal classes into normal java util classes.
> > 
> > [1] https://code.google.com/p/dehibernator/
> 
> Well, not sure about that from performance point of view.
> 
> If we really move away from GWT completely in 4.0, then implementing all
> hibernate inner collections in "uioverride" in a similar way as Tomas did
> seems to me as the best solution from performance and "easiest to remove
> when not needed" point of view.
> 

I took some inspiration from that code and wrote my own fairly simple 
hibernate persistent collection replacer, and I put the patch up here [3]. It 
still uses reflection so it is probably not the fastest thing ever written.

[3] https://gerrit.ovirt.org/#/c/41810/

> > > > Alexander
> > > > 
> > > > > Any better ideas?
> > > > > Thanx,
> > > > > Tomas
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