[hibernate-dev] Hibernate ORM SQL generation

[Steve Ebersole]

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?
>>>>>
>>>> _______________________________________________
>>>>> hibernate-dev mailing list
>>>>> hibernate-dev at lists.jboss.org
>>>>> https://lists.jboss.org/mailman/listinfo/hibernate-dev
>>>>>
>>>>
>>>>
>