[hibernate-dev] 6.0 - Session#createFilter

Tue Jan 3 10:03:50 EST 2017

On 3 January 2017 at 14:26, Steve Ebersole <steve at hibernate.org> wrote:
> The plan with Stream support here is exactly that... translate the map,
> filter etc calls into a SQL query.

Ah, that sounds awesome!

>
>
> 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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>> >>
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>> >>
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