[hibernate-dev] Hibernate ORM SQL generation

[andrea boriero]

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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>>>
>>>