I do want to pull ORM in to the hibernate-sqm module as a test dependency to be able to more easily set up the ModelMetadata stuff based on a SessionFactory. That is possibly awkward later when we then use hibernate-sqm in ORM in terms of having 2 different versions of ORM. I am open to alternatives that don't involve *me* developing a real(ish) ModelMetadata impl from scratch.
On Thu, Aug 27, 2015 at 8:45 AM Gunnar Morling <gun...@hibernate.org> wrote: > 2015-08-26 14:41 GMT+02:00 Steve Ebersole <st...@hibernate.org>: > > On Wed, Aug 26, 2015 at 2:10 AM Gunnar Morling <gun...@hibernate.org> > wrote: > >> > >> Hi Steve, > >> > >> > 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. > >> > >> In which situations will this happen? I can see inheritance where a > >> HQL query targeting a super-type needs to be translated into a SQL > >> query per sub-type table. What others are there? > > > > > > For ORM the only time this happens today for a SELECT query is in the > "split > > query" case I mentioned elsewhere (a query like 'from java.lang.Object'). > > SQM does this much better than we do in ORM today. in SQM we build a > > semantic tree that encodes the "unmapped polymorphism" such that we get a > > tree with 'java.lang.Object' as the root from element. But it is a > > FromElement with a special type of EntityTypeDescriptor (which comes from > > the caller remember): PolymorphicEntityTypeDescriptor. On the ORM side > then > > I have a QuerySplitter that takes that query and makes a copy of that > entire > > SQM tree, one for each mapped implementor of the specified class. FWIW, > ORM > > does this today, albeit in a different way. Today we split the query > based > > on String manip and then feed it parser. Here we feed it to the parser > and > > use the tree to split it; much less brittle :) > > > > Really the cases where this would happen (one "concrete SQM" -> multiple > > SQL) would be UPDATE and DELETE queries against "multi-table structures" > > (inheritance, secondary tables). > > > > > >> For the purposes of OGM this phase ideally would not be tied to SQL, > >> as we phase the same task with non-SQL backends in SQL. I.e. i'd be > >> beneficial to have input -> semantic-tree -> > >> semantic-output-query-tree(s) -> (SQL|non-SQL query). There > >> "semantic-output-query-tree(s)" would be an abstract representation of > >> the queries to be executed, e.g. referencing the table name(s). But it > >> would be unaware of SQL specifics. > > > > > > OGM would be doing this. This SQM is the end result of the shared > library. > > WHat each caller does with the SQM is up to that particular caller. We > > should consider moving QuerySplitter (its in my PoC, which now acts as > the > > PoC for using this in ORM) into the hibernate-sqm module. Any caller > > wanting to support those unmapped class references will need to do the > same > > thing. > > Yes, that'd be good I think. We'd have to apply the same rules for > splitting as ORM. > > > > > BTW, another cool thing to note is the (still expanding) support for > "strict > > JPQL compliance" enforcement. > _______________________________________________ hibernate-dev mailing list hibernate-dev@lists.jboss.org https://lists.jboss.org/mailman/listinfo/hibernate-dev
