code: def get_queryset(self, request):
          
          if request.GET.get(ShowHistoryFilter.parameter_name) == '1':
              queryset = self.model.objects.with_active_flag()
          else:
              # Show only the most recent row for each key.
              queryset = self.model.objects.current_set()
          ordering = self.get_ordering(request)
          if ordering:
              return queryset.order_by(*ordering)
          return queryset
docs: Annote the queryset with an 'is_active' property that's true iff that row is the most
          recently added row for that particular set of KEY_FIELDS values.
          Filter the queryset to show only is_active rows by default.