[hibernate-dev] Hibernate ORM SQL generation

[andrea boriero]

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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