Django admin custom filter that limits the choices for related fields to only those related to the current queryset, based on active filters and search terms. This ensures that dropdowns only show relevant options, improving usability for large datasets.

gistfile1.txt

class LimitedChoiceRelatedListFilter(admin.RelatedOnlyFieldListFilter):
    def field_choices(self, field, request, model_admin):
        qs = model_admin.get_queryset(request)
        for param, value in request.GET.items():
            # ignore reserved keywords
            if param in ["o", "e", "q"]:
                continue
            if value:
                qs = qs.filter(**{param: value})
        # also filter for search
        if "q" in request.GET:
            qs, _ = model_admin.get_search_results(request, qs, request.GET.get("q", ""))
        pk_qs = qs.distinct().values_list(f"{self.field_path}__pk", flat=True)
        return field.get_choices(include_blank=True, limit_choices_to={"pk__in": pk_qs})