Improve typing for filter schema

Author: max-muoto

ninja/filter_schema.py

@@ -1,4 +1,4 @@
-from typing import Any, cast
+from typing import Any, TypeVar, cast
 
 from django.core.exceptions import ImproperlyConfigured
 from django.db.models import Q, QuerySet
@@ -22,6 +22,9 @@
 #     )
 
 
+T = TypeVar("T", bound=QuerySet)
+
+
 class FilterSchema(Schema):
     # if TYPE_CHECKING:
     #     __config__: ClassVar[Type[FilterConfig]] = FilterConfig  # pragma: no cover
@@ -49,7 +52,7 @@ def get_filter_expression(self) -> Q:
         except NotImplementedError:
             return self._connect_fields()
 
-    def filter(self, queryset: QuerySet) -> QuerySet:
+    def filter(self, queryset: T) -> T:
         return queryset.filter(self.get_filter_expression())
 
     def _resolve_field_expression(