code: def get_selected(self, request):
          
          obj = self.get_object()
          queryset = None
          # if single-object URL not used, check for selected objects
          if not obj:
              if request.GET.get(CHECKBOX_NAME):
                  selected = request.GET.get(CHECKBOX_NAME).split(',')
              else:
                  selected = request.POST.getlist(CHECKBOX_NAME)
          else:
              selected = [obj.pk]
  
          queryset = self.get_queryset().filter(pk__in=selected)
          return queryset
docs: Returns a queryset of the selected objects as specified by \
          a GET or POST request.