Thanks, everyone. I sort of realised I'd need an annotation but wasn't too clued up on its use. This is just what I needed.
Best wishes. On Tue, Jul 17, 2012 at 2:05 AM, akaariai <akaar...@gmail.com> wrote: > On 16 heinä, 14:38, Sithembewena Lloyd Dube <zebr...@gmail.com> wrote: > > Hi everyone, > > > > I have a queryset of categories and would like to exclude categories with > > no items associated. I am cycling through the queryset as follows, > without > > the desired result: > > > > for cat in categories: > > if cat.item_set.count() == 0: > > categories.exclude(pk=cat.pk) > > Querysets are always cloned on calling a method, so the right syntax > is: > categories = categories.exclude(pk=cat.pk). > For efficiency reasons you might want to collect all the pks into a > list, and then after the loop do one: > categories = categories.exclude(pk__in=pk_list) > > The queryset cloning can be expensive if you do a lot of operations. > > Of course, the annotation way given downthread is likely to be the > most effective way to do this. > > - Anssi > > -- > 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. > > -- Regards, Sithembewena Lloyd Dube -- 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.
