There has been some light discussion in the Hibernate mailing list lately
regarding antlr4, which seems to have a quite different model compared to
antlr3. According to the postings, it would require a rethinking of how
(N)Hibernate handles the syntax trees.
One thing that always bugs me is that almost everything important seems to
happen inside ("through") constructor calls, or sometime inside method
calls that are written directly as parameters to a constructor call. I find
myself repeatedly stepping over such code during debugging, only to realise
I now have to start over because hidden behind that fairly innocent-looking
new X(y, z, x.GetTranslatorOrWhatever()) was actually the brunt of the
logic.
The way that several antlr parsers are involved also surprised me
originally.
/Oskar
2014-12-10 22:50 GMT+01:00 Gunnar Liljas <gunnar.lil...@gmail.com>:
> I'm currently investigating a bit of query functionality in NHibernate and
> I'm losing all of my hair, since I've ended up in the HqlSqlWalker (there
> generated code part).
>
> I understand why the "new" Linq provider was built on top of the Hql
> parts, but at the same time it's a part of Nhibernate's code base that I
> really, really ha......don't like.
>
> A Linq expression tree is transformed into a ReLinq query model.
> The query model is transformed into an intermediate Hql tree
> The intermediate tree is transformed into "the real" Hql tree
> The Hql tree is eventually transformed into SQL
>
> The performance hit of all this may be neglible, but the complexity hit is
> insane. There is at least one tree to many and the complexity of the
> HqlSqlWalker is making it impossible to work with. It's not meant to be
> worked with, but having core functionality in a black hole is annoying.
> Going from a ReLinq query model to SQL will always be complex stuff, but it
> shouldn't have to be this convoluted.
>
> At some point I think it would make more sense to reverse the model, so
> that the Hql is processed into a syntax tree optimized for productive and
> performant Linq.
>
> Thoughts?
>
> /G
>
> PS. At certain points the HqlSqlWalker calls HandleClauseStart, which sets
> _currentClauseType, There is no corresponding HandleClauseEnd to pop the
> state, which means that _currentClauseType can actually be wrong. In my
> test code that meant that the parser though it was inside a subquery when
> it actually wasn't any longer. Just an example of the kind of weirdness
> that is almost impossible to debug, and even harder to do something about
> once you find the problem. DS
>
>
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