[hibernate-dev] 6.0 - Session#createFilter

[Steve Ebersole]

Well stop and think about it...  What do you expect session.filter( new
ArrayList(), "<some HQL>") to do?

Yes, it has to be a PersistentCollection.  Hibernate handles "persistent
arrays" as well
(see org.hibernate.collection.internal.PersistentArrayHolder), although it
is a discouraged feature.

It is used to apply:

   1. an implicit from-clause element for the collection owner (named
   "this")
   2. a restriction on the PersistentCollection's owner.

So a filter like I mentioned before (`session.createFilter(
customer.getOrders(), "orderDate < currentDate() - {3 months}" )`) is
really the same as (it is literally converted to this internally):

`select elements( this.orders ) from Customer this where this.id =
<this-customer-id> and orderDate < currentDate() - {3 months}`


On Mon, Jan 2, 2017 at 8:45 AM Christian Beikov <christian.beikov at gmail.com>
wrote:

> As far as I understand from the documentation(
> https://docs.jboss.org/hibernate/orm/3.3/reference/en/html/objectstate.html#objectstate-filtering),
> it can be used to filter collections and arrays. I don't know if it only
> works for persistent collections but since arrays are also mentioned, I
> guess not.
> I'd expect the collection or array to be filtered and projected in-memory
> if possible, thus not executing a query unless needed for a lazy collection
> or additional from clause.
>
> If that understanding is wrong, please help me understand what the purpose
> is then.
>
>
> Am 02.01.2017 um 12:37 schrieb Steve Ebersole:
>
> I think you are not understanding createFilter:
>
>
> http://docs.jboss.org/hibernate/orm/current/javadocs/org/hibernate/Session.html#createFilter
>
> Again, to call filter you'd have to have access to the Collection you want
> to filter.
>
> On Mon, Jan 2, 2017 at 2:40 AM Christian Beikov <
> christian.beikov at gmail.com> wrote:
>
> Let's say we have this entity with an attribute that is not directly
> exposed.
>
> class EntityA { String field; }
>
> and then you pass a collection of EntityA instances to createFilter like
>
> Collection<EntityA> collection = ...
> collection = session.createFilter(collection, "field =
> 'abc%'").getResultList();
>
> See my point? Since Hibernate can access the field directly, this works,
> but with streams you'd need to expose the field via a getter so you can
> filter for it.
>
>
> Am 02.01.2017 um 09:25 schrieb Steve Ebersole:
>
> Could you explain the situation where you would map a collection but not
> expose it?  And btw even create createFilter would not work there because
> you have to pass createFilter the collection
>
> On Mon, Jan 2, 2017, 2:15 AM Christian Beikov <christian.beikov at gmail.com>
> wrote:
>
> Well it does when you consider that there might be no getter for a field.
> With createFilter you could still filter the result list without exposing
> direct access to the field via a getter.
>
> Am 02.01.2017 um 08:52 schrieb Steve Ebersole:
>
> Field-access would have zero bearing on this
>
> On Mon, Jan 2, 2017 at 1:30 AM Christian Beikov <
> christian.beikov at gmail.com> wrote:
>
> Sounds good to me, but maybe we could do a poll to see if people are
> using this? I don't know if the filter also works for field based access
> strategy, but that could be a reason for keeping it around.
>
> Regards,
>
> Christian
>
>
> Am 31.12.2016 um 21:00 schrieb Steve Ebersole:
> > As I have not been hearing hardly any feedback on these 6.0 design
> > questions I have been trying to start, I'll be doing something different
> in
> > this and any additional emails.. I'll state what I propose to do and if
> > anyone has issue with it they can make a counter proposal.  Otherwise I
> > plan on following through with my proposal.
> >
> > I plan on removing Session#createFilter.  There are numerous reasons why
> > which I can discuss if anyone is interested in exploring this.
> >
> > Ultimately I think it makes sense to handle this via Java 8 streams[1]
> > although I am not sure that needs to happen in 6.0
> >
> > [1] https://hibernate.atlassian.net/browse/HHH-10962
> > _______________________________________________
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> > hibernate-dev at lists.jboss.org
> > https://lists.jboss.org/mailman/listinfo/hibernate-dev
>
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