code: def filter_facet_queryset(self, queryset):
          
          for backend in list(self.facet_filter_backends):
              queryset = backend().filter_queryset(self.request, queryset, self)
  
          if self.load_all:
              queryset = queryset.load_all()
  
          return queryset
docs: Given a search queryset, filter it with whichever facet filter backends
          in use.