> On May 22, 12:51 pm, sk <6b656...@gmail.com> wrote: > > > > > > > If I have a hierarchy of models such that: > > > class A(models.Model): > > name = CharField(max_length=10) > > > class B(models.Model): > > name = CharField(max_length=10) > > a= ForeignKey(A) > > > class C(models.Model): > > name = CharField(max_length=10) > > b= ForeignKey(B) > > > If I have an instance of C, as returned by: > > > c = C.objects.get(pk=1) > > > How do I get the name of A? > > > I realise I can go via B, but I am hoping to be able to follow the > > chain back to A from any arbitrary point in (a much longer) chain. > > > For example: > > If this was repeated up to F in an identical manner. > > If I pass a function any instance from A to F I would want to return > > A.name. > > > I am sure there must be a simple way to get the root data, but I am > > having trouble finding it. > > You really do have to go through the relations through the chain - > there is no direct links from C to A so it is impossible to just hop > from C to A. > > You can query the A instance by something like > A.objects.filter(pk=B.objects.filter(pk=c.b_id)) - this should return > the A instance in one query. (It might be you will need to use > pk__in). > > Or, you could use select_related or prefetch_related to do the > fetching. > > - Anssi- Hide quoted text - > > - Show quoted text -
Fair enough, thank you for your reply. I is it posible to 'follow the chain' without knowing the exact instance you are in? for example can i get all foreign keys for a given instance, then follow them? To be honest this is just for interest now - I have implemented this with some hard-coding of how to decide where you are in the 'tree'. Many thanks Stephen -- 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.
