At a guess, I would say that the Python code "Foo.bar != bar" means that you are looking for Foo objects that aren't related to bar. This includes Foos that are related to a *different* Bar instance, as well as Foos that aren't related to *any* bar instance. In sql terms, foo.bar_id != bar.id OR foo.bar_id is NULL.
Whereas in the other instance, you've asked for something more specific, so that's what SA has given you. Simon > On 31 Oct 2014, at 16:36, Ladislav Lenart <lenart...@volny.cz> wrote: > > Hello. > > I have just noticed (by accident) a semantic difference of the not-equal > operator (!=), depending on the style used. For example a query > > session.query(Foo).filter(Foo.bar_id != bar.id) > > produces SQL like (expected) > > SELECT * > FROM foo > WHERE foo.bar_id != %(bar_id_1)s > > whereas a query > > session.query(Foo).filter(Foo.bar != bar) > > produces SQL like (NOT expected) > > SELECT * > FROM foo > WHERE ( > foo.bar_id != %(bar_id_1)s > OR foo.bar_id IS NULL > ) > > I thought that > > Foo.bar != bar > > is just a shortcut for > > Foo.bar_id != bar.id > > Is this difference intentional? > May I know why (i.e. the motivation)? > > > Thanks in advance, > > Ladislav Lenart > > -- > 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. -- 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.
