On Wed, Oct 22, 2014 at 7:02 PM, Michael Bayer <mike...@zzzcomputing.com> wrote: > Yeah i think that is what you have to do, you want UNION but you want all the > criteria generated on the inside. There’s two approaches to take here, > either start with the UNION that polymorphic gives you, the rewrite it: > > SELECT u.* FROM (SELECT * FROM a UNION SELECT * FROM b) AS u WHERE u.x = y > > becomes -> SELECT * FROM a WHERE a.x=y UNION SELECT * FROM b WHERE b.x=y > > or you can catch each SELECT as they are created earlier, before you build > the UNION. The first approach might be a little harder to implement but it > might be more robust.
That's a great idea, but it looks like more work than I have time available now. I'll definitely try to do something like that later. > SQLAlchemy does things like this all the time but they are not trivial to > implement as you need to think about the whole expression. The visitor > system in sqlalchemy.sql.visitors forms the basis for how operations like > this are usually done, providing an interface used to scan and rebuild > expressions. Whole-query rebuilds like that can be tricky, we for example > do one against SQLite when we have a SELECT that has nested JOINs (see > http://docs.sqlalchemy.org/en/rel_0_9/changelog/migration_09.html#many-join-and-left-outer-join-expressions-will-no-longer-be-wrapped-in-select-from-as-anon-1, > the code that does this is at > https://bitbucket.org/zzzeek/sqlalchemy/src/56d5732fbdf09508784df6dc4c04e5b39ac6be85/lib/sqlalchemy/sql/compiler.py?at=master#cl-1330. That's really helpful for me right now. I'm using the cloning visitor to rebuild the expressions from the recorded filter() calls for the secondary models and it works like a charm. Thanks for the help. -- --- Pedro Werneck -- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To unsubscribe from this group and stop receiving emails from it, send an email to sqlalchemy+unsubscr...@googlegroups.com. To post to this group, send email to sqlalchemy@googlegroups.com. Visit this group at http://groups.google.com/group/sqlalchemy. For more options, visit https://groups.google.com/d/optout.
