I looks like my attempt to simplify and abstract the problem just made it harder to help me: my apologies for that. I was trying to combined two different problems rather than ask two questions. Thanks for helping despite that.
I think I have a solution for most of my problems, as far as getting the queries working. I might be back with questions about optimisation, but I can live with a little inefficiency in the query I need to get working first. On Aug 28, 4:33 am, Matteius <matte...@gmail.com> wrote: > Since you are combining two sets of different objects you'll want > Gelonida's response. Additionally, Use Q to create more logically > advanced queries. I find your language difficult to gather what query > you are looking for exactly, but here is an example of what I think > you might mean: > > from django.db.models import Q > > the_Ds = D.objects.all().filter(b=B) > the_Es = E.objects.all().filter(c=C) > > combined = the_Ds | the_Es > > # Other Example (an & requires both constraints to be met, and an Or > will include the set of all matches. > the_As = A.objects.all().filter(Q(constraint1) & Q(constraint2)) > the_Bs = B.objects.all().filter(Q(constraint1) | Q(constraint2)) > > -Matteius > > Don't overlook how powerful this is because Django has Manager classes > so you can make your constraints refer to both local properties and > foreign key constraints as well as properties within the foreign key > lookups. You may find that you wish to edit your schema relationship, > perhaps by pointing backwards or reversing the relationship. It is > hard to say with the categorical A, B, C, D example, but hope this > helps and Good Luck! > > On Aug 27, 3:47 pm, Gelonida N <gelon...@gmail.com> wrote: > > > > > > > > > On 08/27/2011 11:39 AM, graeme wrote: > > > > I have a some models related link this: > > > > A has a foreign key on B which has a foreign key on C > > > > I also have D with a foreign key on B, and E with a foreign key of C > > > > If I do A.filter(**args).select_related() I will get all the As, Bs, > > > and Cs I want. > > > > How do I get the Ds with a foreign key on a B in my queryset > > > (preferably filtered) and all Es with a foreign key on C (also > > > preferably filtered) > > > > The best I have been able to come up with is to query for all the the > > > Ds and Es I want, and combine them with the Bs and Cs in the view. > > > > I have a similar problem with another site, except that there not > > > every B I want has an A with a foreignkey pointing to it, so I cannot > > > just do select_related on A. > > > > I am not worried about doing an extra query or two per page. What I > > > want to avoid is doing an extra query for each object in a lengthy > > > list. > > > You can 'or' two query sets with the '|' operator > > > so do > > queryset1 = Mymodel.objects.all().filter(...) > > qyeryset2 = Mymodel.objects.all().filter(...) > > > combined = queryset1 | queryset2 -- 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.