How to get a django QuerySet of all ForeignKeys of all objects in a Queryset
foo_queryset = Foo.objects.filter(attr=value)
referenced_bars = Bar.objects.filter(id__in=foo_queryset.values('bar_id'))
foo_queryset = Foo.objects.filter(attr=value)
referenced_bars = Bar.objects.filter(id__in=foo_queryset.values('bar_id'))