[hibernate-dev] Hibernate ORM SQL generation

Mon Aug 24 08:40:42 EDT 2015

 I have nothing against your proposal so +1

On 24 August 2015 at 04:55, Steve Ebersole <steve at hibernate.org> wrote:

> Another point I want to discuss up from because it affects tree
> structure.  Specifically the idea of an "unbounded implicit inheritance"
> query.  These are queries like "from java.lang.Object".  Queries where the
> from clause pulls in "unmapped inheritance".  These are fine, to an
> extent.  Hibernate has natively supported these since way back[1].
>
> What is problematic is cases where we have more than one "unmapped
> inheritance" reference.  E.g. "from java.lang.Object o1, java.lang.Object
> o2".  In fact its the same difficulty as an unbounded cartesian product,
> but here in terms of the number of SQL queries we need to produce/execute.
>
> So I propose that we allow just one "unmapped inheritance" reference per
> query.
>
> [1] Reminder to self... another "strict JPQL compliance" consideration.
>
> On Sat, Aug 22, 2015 at 1:16 PM Steve Ebersole <steve at hibernate.org>
> wrote:
>
>> I got that initial refactoring pushed to my fork...
>>
>> On Fri, Aug 21, 2015 at 3:51 PM Steve Ebersole <steve at hibernate.org>
>> wrote:
>>
>>> Just a heads up that I started a major refactoring of the antlr4 poc
>>> project in preparation for starting to look at this next sql-gen step.
>>>
>>> First I am making it into a multi-module project.  We will have the
>>> hql-parser module, but then also an orm-sql-gen module to be able to play
>>> with that part.  This makes sure we are not blending orm concerns into the
>>> pure hql parser.
>>>
>>> Also, I started working on splitting the "semantic query" model out into
>>> a separate module as well.  There are a few reasons for this.  I wont go
>>> into them all here.  The main one being that HQL is just one producer of
>>> this semantic model.   Rather than another long name I went with the
>>> acronym SQM (Semantic Query Model) here.  The top package being
>>> org.hibernate.sqm.
>>>
>>> These changes already illustrated some tighter couplings then I had
>>> intended, so it was a good exercise.  I'll push once I get those couplings
>>> cleaned up.
>>>
>>> On Fri, Aug 21, 2015 at 2:35 PM andrea boriero <dreborier at gmail.com>
>>> wrote:
>>>
>>>> I haven't seen it, I'm going to read it.
>>>>
>>>> On 21 August 2015 at 16:54, Steve Ebersole <steve at hibernate.org> wrote:
>>>>
>>>>> http://www.antlr2.org/article/1170602723163/treewalkers.html
>>>>>
>>>>> Not sure if y'all have seen this.  Its an old article advocating
>>>>> manual tree walking (what we are facing here) over using generated tree
>>>>> walkers.
>>>>>
>>>>>
>>>>>
>>>>> On Wed, Aug 19, 2015 at 12:27 PM Steve Ebersole <steve at hibernate.org>
>>>>> wrote:
>>>>>
>>>>>> I agree.  Its my biggest hang up with regard to using Antlr 4.
>>>>>> Actually, its my only hang up with Antlr 4, but its a huge one.
>>>>>>
>>>>>> On Tue, Aug 18, 2015 at 9:30 AM andrea boriero <dreborier at gmail.com>
>>>>>> wrote:
>>>>>>
>>>>>>> yes Steve I'm more familiar with Antlr4 ( but not 3) and I gave a
>>>>>>> look at your poc.
>>>>>>>
>>>>>>> Apart some problems to fully understand the semantic model (due to
>>>>>>> my lack of a complete knowledge of the domain problem),
>>>>>>> I agree with you about the simplicity and elegance of  the grammar
>>>>>>> for HQL recognition and semantic model building.
>>>>>>>
>>>>>>> What I don't like it's the necessity to build our own semantic model
>>>>>>> walker/s in order to produce the final SQL.
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> On 14 August 2015 at 16:32, Steve Ebersole <steve at hibernate.org>
>>>>>>> wrote:
>>>>>>>
>>>>>>>> We've had a few discussions about this in the past.  As 5.0 is
>>>>>>>> getting
>>>>>>>> close to Final (next week), its time to start contemplating our
>>>>>>>> next major
>>>>>>>> tasks.  The consensus pick for that has been the idea of a "unified
>>>>>>>> SQL
>>>>>>>> generation engine" along with a shared project for the semantic
>>>>>>>> analysis of
>>>>>>>> HQL/JPQL (and recently it was decided to include JPA Criteria
>>>>>>>> interpretation here as well).
>>>>>>>>
>>>>>>>> The central premise is this.  Take the roughly 6 or 7 different
>>>>>>>> top-level
>>>>>>>> ways Hibernate generates SQL and combine that into one "engine"
>>>>>>>> based on
>>>>>>>> the input of a "semantic tree".  The mentioned HQL/JPQL/Criteria
>>>>>>>> shared
>>>>>>>> project will be one producer of such semantic trees.  Others would
>>>>>>>> include
>>>>>>>> persisters (for insert/update/delete requests) and loaders (for load
>>>>>>>> requests).
>>>>>>>>
>>>>>>>> We have a lot of tasks for this overall goal still remaining.
>>>>>>>>
>>>>>>>> We still have to finalize the design for the HQL/JPQL/Criteria to
>>>>>>>> semantic
>>>>>>>> tree translator.  One option is to proceed with the Antlr 4 based
>>>>>>>> approach
>>>>>>>> I started a PoC for.  John has been helping me some lately with
>>>>>>>> that.  The
>>>>>>>> first task here is to come to a consensus whether Antlr 4 is the
>>>>>>>> way we
>>>>>>>> want to proceed here.  We've been over the pros and cons before in
>>>>>>>> detail.
>>>>>>>> In summary, there is a lot to love with Antlr 4.  Our grammar for
>>>>>>>> HQL
>>>>>>>> recognition and semantic tree building is very simple and elegant
>>>>>>>> imo.  The
>>>>>>>> drawback is clearly the lack of tree walking, meaning that we are
>>>>>>>> responsible for writing by hand our walker for the semantic tree.
>>>>>>>> In fact
>>>>>>>> multiple, since each consumer (orm, ogm, search) would need to
>>>>>>>> write their
>>>>>>>> own.  And if we decide to build another AST while walking the
>>>>>>>> semantic
>>>>>>>> tree, we'd end up having to hand-write yet another walker for those.
>>>>>>>>
>>>>>>>> What I mean by that last part is that there are 2 ways we might
>>>>>>>> choose to
>>>>>>>> deal with the semantic tree.  For the purpose of discussion, let's
>>>>>>>> look at
>>>>>>>> the ORM case.  The first approach is to simply generate the SQL as
>>>>>>>> we walk
>>>>>>>> the semantic tree; this would be a 2 phase interpretation approach
>>>>>>>> (input
>>>>>>>> -> semantic tree -> SQL).  That works in many cases.  However it
>>>>>>>> breaks
>>>>>>>> down in other cases.  This is exactly the approach our existing HQL
>>>>>>>> translator uses.  The other approach is to use a 3-phase
>>>>>>>> translation (input
>>>>>>>> -> semantic-tree -> semantic-SQL-tree(s) -> SQL).  This gives a
>>>>>>>> hint to one
>>>>>>>> of the major problems.  One source "semantic" query will often
>>>>>>>> correspond
>>>>>>>> to multiple SQL queries; that is hard to manage in the 2-phase
>>>>>>>> approach.
>>>>>>>> And not to mention integrating things like follow-on fetches and
>>>>>>>> other
>>>>>>>> enhancements we want to gain from this.  My vote is definitely for
>>>>>>>> 3 or
>>>>>>>> more phases of interpretation.  The problem is that this is exactly
>>>>>>>> where
>>>>>>>> Antlr 4 sort of falls down.
>>>>>>>>
>>>>>>>> So first things first... we need to decide on Antlr 3 versus Antlr 4
>>>>>>>> (versus some other parser solution).
>>>>>>>>
>>>>>>>> Next, on the ORM side (every "backend" can decide this
>>>>>>>> individually) we
>>>>>>>> need to decide on the approach for semantic-tree to SQL
>>>>>>>> translation, which
>>>>>>>> somewhat depends on the Antlr 3 versus Antlr 4 decision.
>>>>>>>>
>>>>>>>> We really need to decide these things ASAP and get moving on them
>>>>>>>> as soon
>>>>>>>> as ORM 5.0 is finished.
>>>>>>>>
>>>>>>>> Also, this is a massive undertaking with huge gain potentials for
>>>>>>>> not just
>>>>>>>> ORM.  As such we need to understand who will be working on this.
>>>>>>>> Sanne,
>>>>>>>> Gunnar... I know y'all have a vested interest and a desire to work
>>>>>>>> on it.
>>>>>>>> John, I know the same is true for you.  Andrea?  Have you had a
>>>>>>>> chance to
>>>>>>>> look over the poc and/or get more familiar with Antlr?
>>>>>>>>
>>>>>>> _______________________________________________
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>>>>>>>> hibernate-dev at lists.jboss.org
>>>>>>>> https://lists.jboss.org/mailman/listinfo/hibernate-dev
>>>>>>>>
>>>>>>>
>>>>>>>
>>>>