On Sat, Oct 8, 2011 at 8:18 AM, Michal Petrucha <michal.petru...@ksp.sk> wrote: > Behind the scenes, Django does a JOIN. Its type (INNER od LEFT OUTER) > is decided based on whether the left-hand column (your ForeignKey > field) is allowed to be NULL or not.
the weird part, is that is takes the same choice on reverse relationships, which isn't necessarily appropriate. for example, model A has a foreign key to B. when reading A records with select_related, it makes sense that if the FK is NULLable, it uses a LEFT OUTER join while if it's not NULLable, use an INNER join. when I have a B object, it's _really_ handy to have the reverse relationship set up for me; but what if i want to select those B objects that doesn't have any A? this works... B.objects.filter(a_set__isnull=True) but only if the FK from A to B has the null=True argument. and if I want to make the FK from A to B non-NULLable? maybe an A record doesn't make any sense without B, but B without any A does. so i don't put (null=True); so in the query above, i get an INNER join followed by the condition that a.id IS NULL, and the result set is empty. :-( the only solution i've found is to make the FK NULLable, even when it doesn't make sense. I'd love to see a separate reverse_null=True argument (by default reverse_null==null) on the FK, that would make the reverse join a LEFT OUTER one while still prohibiting an A record without B. am i missing something? -- Javier -- You received this message because you are subscribed to the Google Groups "Django users" group. To post to this group, send email to django-users@googlegroups.com. To unsubscribe from this group, send email to django-users+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/django-users?hl=en.
