removing a is_gfk field flag

django/contrib/admin/utils.py

@@ -296,7 +296,7 @@ def _get_non_gfk_field(opts, name):
     should be treated as not found by the 'label_for_field' function.
     """
     field = opts.get_field(name)
-    if getattr(field, 'is_gfk', False):
+    if field.has_relation and field.one_to_many and not field.related_model:
         raise models.FieldDoesNotExist()
     return field
 

django/contrib/contenttypes/fields.py

@@ -21,10 +21,6 @@ class GenericForeignKey(FieldFlagsMixin):
     Provides a generic relation to any object through content-type/object-id
     fields.
     """
-    # Adding a specific flag to identify GenericForeignKey without having to
-    # import base class and do instance check
-    is_gfk = True
-
     related_model = None
     editable = False
     is_reverse_object = False

django/db/models/options.py

@@ -360,7 +360,7 @@ def fields(self):
         # these three filters as filters to the generator.
         is_not_an_m2m_field = lambda f: not (f.has_relation and f.many_to_many)
         is_not_a_generic_relation = lambda f: not (f.has_relation and f.many_to_one)
-        is_not_a_generic_foreign_key = lambda f: not hasattr(f, 'is_gfk')
+        is_not_a_generic_foreign_key = lambda f: not (f.has_relation and f.one_to_many and not f.related_model)
 
         return make_immutable_fields_list("fields", (f for f in self.get_fields(reverse=False) if
                                           is_not_an_m2m_field(f) and is_not_a_generic_relation(f)

django/db/models/sql/query.py

@@ -1349,9 +1349,10 @@ def names_to_path(self, names, opts, allow_many=True, fail_on_missing=False):
             try:
                 field = opts.get_field(name)
 
-                # Fields like a GenericForeignKey cannot generate reverse relations
-                # therefore they cannote be used for reverse querying.
-                if hasattr(field, 'is_gfk'):
+                # Fields that contain one-to-many relations with a generic model (like a
+                # GenericForeignKey) cannot generate reverse relations Therefore they
+                # cannote be used for reverse querying.
+                if field.has_relation and not field.related_model:
                     raise FieldError("Field %r is a GenericForeignKey. This field "
                                      "type does not generate a reverse relation "
                                      "by default and therefore cannot be used for "