Add utility methods to managed_by manager

aleksis/core/managers.py

@@ -14,9 +14,16 @@ from polymorphic.managers import PolymorphicManager
 class AlekSISBaseManager(_CurrentSiteManager):
     """Base manager for AlekSIS model customisation"""
 
-    def get_queryset(self):
-        qs = super().get_queryset()
-        return qs.filter(managed_by_app_label="")
+    def unmanaged(self) -> QuerySet:
+        """Get instances that are not managed by any particular app."""
+        return super().get_queryset().filter(managed_by_app_label="")
+
+    def managed_by_app(self, app_label: str) -> QuerySet:
+        """Get instances managed by a particular app."""
+        return super().get_queryset().filter(managed_by_app_label=app_label)
+
+    def get_queryset(self) -> QuerySet:
+        return self.unmanaged()
 
 
 # FIXME rename this and other classes after removing sites framework