Re: [hibernate-dev] Treat support

Hi Emond, thanks for the list, I already linked some of the issues you opened. HHH-10561, HHH-10759, HHH-10767 and HHH-11062 are apparently bugs in the Criteria to HQL/JPQL rendering and I am trying to directly target the HQL/JPQL parts. Regarding HHH-10768 see the comments on the issue. Regards, Christian Am 23.08.2016 um 11:36 schrieb Emond Papegaaij: > Hi Christian, > > In the past few months I've reported quite a few bugs on treat support in > Hibernate. I think some of them are already covered by your tests, but not > all. You might want to add those to your tests. These are the issues I've > reported: > https://hibernate.atlassian.net/browse/HHH-10561 > https://hibernate.atlassian.net/browse/HHH-10759 > https://hibernate.atlassian.net/browse/HHH-10767 > https://hibernate.atlassian.net/browse/HHH-10768 > https://hibernate.atlassian.net/browse/HHH-11062 > > Best regards, > Emond > > On dinsdag 23 augustus 2016 11:07:22 CEST Christian Beikov wrote: >> Hi, >> >> so I finished my work on the testsuite >> <https://github.com/beikov/jpa-treat-variations> for the treat operator. >> I also started a forum topic for this discussion: >> https://forum.hibernate.org/viewtopic.php?f=1&t=1043553 >> If anyone is interested, I also started a discussion in the EclipeLink >> forum about that: >> https://www.eclipse.org/forums/index.php/mn/msg/1080319/1/on/0/?SQ=5ddc74 >> f60 1d6750e4794121738a57076 >> >> I hope we can all agree on an interpretation of how treat should work >> and hopefully get a clarification into the spec. Or at least some TCK >> tests, as it doesn't seem to assert anything useful right now. >> >> Regards, >> Christian >> >> Am 09.08.2016 um 13:14 schrieb Christian Beikov: >>> Hello again, >>> >>> I finished the first part of the test cases for root treats and >>> many-to-one treats. I also tried to explain how I would expect treat >>> to work and present a reduction/translation strategy to be able to >>> reduce thinking just about the base cases. >>> Could you comment on that? >>> https://github.com/beikov/jpa-treat-variations/blob/master/src/test/java >>> /j >>> pa/test/TreatVariationsTest.java The tests show various problems with >>> Hibernate as well as EclipseLink. I will add findings from Datanucleus >>> as >>> soon as the relation mapping for table per class is supported. >>> >>> Here is a collection of JIRAs for treat problems >>> >>> * https://hibernate.atlassian.net/browse/HHH-10988 >>> * https://hibernate.atlassian.net/browse/HHH-9345 >>> * https://hibernate.atlassian.net/browse/HHH-9862 >>> * https://hibernate.atlassian.net/browse/HHH-10768 >>> * https://hibernate.atlassian.net/browse/HHH-9594 >>> >>> The definition of the semantics according to JPA spec 4.4.9 are a bit >>> strange as it does not distinguish between FROM and WHERE clause when >>> mentioning filtering on the subtype. >>> It specifically says "Use of the TREAT operator therefore also has the >>> effect of filtering on the specified type (and its subtypes) as well >>> as performing the downcast" and I think this is only relevant for >>> treats in the FROM clause. >>> Treats in the WHERE clause should not result in filtering. Depending >>> on the join type which is used for the treat path, the result of the >>> treat is either the subtype instance, or may be NULL in case of a left >>> join. >>> Since any comparison(except NULL aware operations) with NULL will >>> eventually result in FALSE according to the SQL spec, the requirement >>> for the treat operator in the WHERE clause to result in FALSE for >>> instances that are not a subtype is also fulfilled. >>> The section "... and in the case of a restriction, the associated >>> predicate is false." didn't consider NULL aware operations so I think >>> this is an oversight. >>> >>> Am 04.08.2016 um 15:52 schrieb Steve Ebersole: >>>> Hey Christian, >>>> >>>> In general terms, one of the items on the docket for SQM is better >>>> TREAT support; but there is a lot that goes into that statement. One >>>> aspect is what we support in the parser properly in terms of >>>> recognition. Another is how this translates into the generates SQL >>>> query. All of this is being looked at with SQM. >>>> >>>> Also, relatedly, better support for switching on/off JPQL-compliance >>>> checking is a goal. >>>> >>>> <background> >>>> TREAT is an explicit downcast operator. It allows you to down cast a >>>> type reference in order to reference one of its subclass attributes. >>>> HQL actually supports implicit downcasting (subclass attribute >>>> references). In a way you can think of HQL as offering TREAT support >>>> implicitly. >>>> </background> >>>> >>>> With all that in mind, see my comments inline... >>>> >>>> >>>> On Wed, Aug 3, 2016 at 9:43 PM Christian Beikov >>>> >>>> <christian.beikov(a)gmail.com <mailto:christian.beikov@gmail.com>> wrote: >>>> * Missing support for treated paths like "TREAT(...).property" >>>> >>>> in the >>>> >>>> parser. This is more or less workaroundable for non-root path >>>> treats. Since root paths can't be treat joined to my >>>> >>>> knowledge, some >>>> >>>> treated paths simple can't be used. Maybe in 90% of the cases >>>> hibernate will just resolve to the right property without >>>> needing >>>> the treat? >>>> >>>> I'm not sure what you mean by "root paths can't be treated". You >>>> mean literally the query root? As in "MyEntity e" in "select e from >>>> MyEntity e"? If so, yes JPA does not allow for that to be TREAT'ed; >>>> but really it makes no sense to allow TREAT there, if you step back >>>> and look at it. A query like "select e from TREAT(MyEntity as MySub) >>>> e" makes no sense; its ultimately just the same as "select e from >>>> MySub e". Arguably I guess it *could* make some sense *if* MySub is >>>> a sub MappedSuperclass since technically JPA also allows only >>>> entities as query roots (HQL does not have this restriction). >>>> >>>> As discussed above, assuming that "someProp" is a persistent property >>>> defined on MySub, this is a perfectly valid HQL: "select e.someProp >>>> from MyEntity e". It is not however valid JPQL; in JPQL you'd have >>>> to say: "select treat( e as MySub).someProp from MyEntity e" >>>> >>>> All that said, the inability to dereference a TREAT'ed path (the >>>> ".property" part) would be a bug, and tbh I am surprised that you say >>>> this does not work with Hibernate. Which of your tests show this not >>>> working? Is there a related Jira? >>>> >>>> * Missing support for a special case of treat join which >>>> apparently >>>> >>>> was overseen by the JPA spec which would be >>>> >>>> "TREAT(TREAT(rootPath AS >>>> >>>> Subtype).relation AS RelationSubtype)". Eclipselink not only >>>> >>>> allows >>>> >>>> this syntax but for inner joins also implements the >>>> appropriate >>>> logic. I am thinking that this might even work in hibernate >>>> >>>> without >>>> >>>> the inner treat, but would fail for attributes with same >>>> names. >>>> >>>> Do you mean specifically the nesting of TREAT operators? Again, I am >>>> surprised that this would not work. Tests? Jira? >>>> >>>> * Joins for supertypes and conditions on discriminators are not >>>> >>>> aware >>>> >>>> of the join type actually used in the treated join => left >>>> join >>>> should cascade up the type hierarchy and discriminator checks >>>> >>>> should >>>> >>>> contain OR DTYPE IS NULL for left join semantics. If treats >>>> >>>> are in >>>> >>>> subconditions the DTYPE checks might even be wrong >>>> >>>> This "restriction" aspect is honestly Hibernate's biggest shortcoming >>>> in its TREAT support. Hibernate's "SQL generation machinery" simply >>>> was not built to support this. At all. I hacked together some >>>> support for TREAT on top of that legacy "SQL generation machinery", >>>> but it is very limited. >>>> >>>> This aspect is specifically what we have discussed in terms of TREAT >>>> support improvements in SQM. Keeping track of where the TREAT occurs >>>> so that we can later know how to properly handle it, whether that >>>> means we can skip parts of the inheritance join tree or maybe need to >>>> render some extra WHERE-clause restrictions... >>>> >>>> * Joins are generated for the whole hierarchy not only the >>>> >>>> types that >>>> >>>> are treated => this might seem to be "just" a performance >>>> >>>> problem, >>>> >>>> but IMO actually is a correctness problem as it makes a >>>> >>>> difference >>>> >>>> if you get e.g. 2 rows or 2 * TYPES rows especially for count >>>> >>>> queries. >>>> >>>> Generating the joins for the whole hierarchy is important for HQL's >>>> implicit downcasting support. However, that said, there are attempts >>>> to restrict that already in place. IIRC this only works for TREATs >>>> that occur in the FROM-clause specifically. However, I thought that >>>> other TREAT operations were still handled in terms of adding >>>> restrictions when dictated. So this might be specific to certain >>>> circumstances. >>>> >>>> Again, which specific tests show this? Jira? >>>> >>>> ---- >>>> >>>> Some specifics of the plan... >>>> >>>> First, internally within the query AST I want to make sure that we >>>> model *all* downcasts whether they are implicit or explicit. In >>>> other words, in terms of AST both of these queries would result in >>>> >>>> the same structure: >>>> 1. select e.someProp from MyEntity >>>> 2. select treat(e as MySub).someProp from MyEntity >>>> >>>> Secondly, we need to keep track of various pieces of information >>>> pertaining to a downcast >>>> (see >>>> org.hibernate.sqm.query.from.Downcast/org.hibernate.sqm.query.from.Down >>>> c >>>> astable).>> >>>> >>>> This includes info like: >>>> 1. The downcast "target" >>>> 2. The context in which the downcast occurred >>>> 3. Any/all contexts in which the downcast is used. >>>> >>>> The last 2 items there would specifically lead to: >>>> * Which specific inheritance joins are needed - and may indicate >>>> >>>> join type >>>> >>>> * Any extra restrictions we may need to add >> >> _______________________________________________ >> hibernate-dev mailing list >> hibernate-dev(a)lists.jboss.org >> https://lists.jboss.org/mailman/listinfo/hibernate-dev > > _______________________________________________ > hibernate-dev mailing list > hibernate-dev(a)lists.jboss.org > https://lists.jboss.org/mailman/listinfo/hibernate-dev _______________________________________________ hibernate-dev mailing list hibernate-dev(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/hibernate-dev