answering myself, well... for the record. > i'm back into my hierachy/graph of objects, which has many paths > reaching from one end to another - A-Z, A-B-Z, A-B-C-Z etc. Using > hierarchical OR (AND (OR ...))) works but gets very slow as all the > 20+ tables involved go in same FROM clause.
> so i have these questions: > - (theoretical) can the alternative made by many ORs over > subexpressions at same level be represented with UNION of things > made from those subexpressions? yes. the difference is in magnitudes, and moreover, union' space grows slowly/linearly while the other grows exponentialy. it can be done at more levels if needed; each OR-ing is a candidate for it. Further tweaking can be made, including not using a union but doing several queries for the 1st-level alternatives (but losing overall order_by etc). > - can i use query().join() to form the expression and stick it > into the union somehow? should i take query.criterion or something else? yes q = query(A).whatever-joins-filters() s = q._compile_context().statement use s for the union's elements. do not forget to add to each q all relevant joins and filters that have been taken outside the (or/and/or/..) parenthesis in the initial big query. then, myunion = union( *allthese) > - can then the union be put into the query of say root > object? yes. use query(A).select_from( myunion) other ways: - query(A).from_statement( myunion) works but does not allow further joins/filters. Although the union is just different As, it will not be treated as such. - one can make a secondary mapper if the query structure is static: m = sa.mapper( A, table=myunion, non_primary=True ) r = session.query( m).whatever ... btw this is going towards query arithmetics that i've been talking since long time. i hope one day things like this will be in SA as a sort of 3rd layer over sql and plain orm. ciao svilen www.svilendobrev.com / dbcook.sf.net --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To post to this group, send email to sqlalchemy@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en -~----------~----~----~----~------~----~------~--~---
