[hibernate-dev] 6.0 - Session#createFilter

Tue Jan 3 09:26:41 EST 2017

The plan with Stream support here is exactly that... translate the map,
filter etc calls into a SQL query.

On Tue, Jan 3, 2017 at 4:41 AM Sanne Grinovero <sanne at hibernate.org> wrote:

> I wonder if "use streams" is a reasonable replacement for all power
> users who might have needed this? We know by experience there's loads
> of such people not reading this list, so maybe we'd need a deprecation
> cycle.
> I don't mean to dive deeply in implementation details and plans, but I
> suspect that the createFilter approach was able to limit the amount of
> data we pump out of the database into the Java heap, while a solution
> based on Java8 streams would post-filter the data, unless you plan to
> have Hibernate able to convert all filter predicates into SQL? (which
> sounds awesome but I wasn't expecting that soon..)
>
> Just wondering if that might be unacceptable to people mapping very
> large collections.
>
> Thanks,
> Sanne
>
>
> On 2 January 2017 at 15:41, Steve Ebersole <steve at hibernate.org> wrote:
> > Christian and I chatted on HipChat.  It seems his confusion stems
> partially
> > from misunderstanding #createFilter, but also the fact that I did not go
> > into detail regarding the plans for this streaming support.  I thought it
> > would be a good idea to discuss that at a high level here.  The main
> thing
> > to bear in mind is that intention is such that there stream calls would
> be
> > translated into SQL rather than resolved in memory (aka get a huge
> > ResultSet and filter etc based on the stream calls).
> >
> > This email was just meant to discuss the removal of the #createFilter
> > method so I did not go into detail.  Also too, the design of that is
> still
> > a discussion point.  Initially I am thinking it would leverage the JPA
> > metamodel, e.g. the static metamodel (the generated Order_ stuff).
> >
> > I should also point out that I completely plan to remove #createFilter in
> > 6.0 and not introduce this streaming stuff until 6.x.  6.0 is already
> > getting beyond its initial scope and I's much rather get 6.0 released
> > earlier and "oftener" :)
> >
> > On Mon, Jan 2, 2017 at 9:11 AM Steve Ebersole <steve at hibernate.org>
> wrote:
> >
> >> 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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