[hibernate-dev] Hibernate ORM SQL generation

[Steve Ebersole]

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.
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> 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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