Reverted "Fixed #24146 -- Fixed a missing fields regression in admin checks."

This reverts commit e8171daf0c.

A new solution is forthcoming.

django/db/models/options.py

@@ -487,12 +487,6 @@ class Options(object):
 
     @cached_property
     def fields_map(self):
-        return self._get_fields_map()
-
-    def _get_fields_map(self):
-        # Helper method to provide a way to access this without caching it.
-        # For example, admin checks run before the app cache is ready and we
-        # need to be able to lookup fields before we cache the final result.
         res = {}
         fields = self._get_fields(forward=False, include_hidden=True)
         for field in fields:
@@ -537,26 +531,20 @@ class Options(object):
 
             return field
         except KeyError:
-            pass
+            # If the app registry is not ready, reverse fields are
-
+            # unavailable, therefore we throw a FieldDoesNotExist exception.
-        if m2m_in_kwargs:
-            # Previous API does not allow searching reverse fields.
-            raise FieldDoesNotExist('%s has no field named %r' % (self.object_name, field_name))
-
-        # If the app registry is not ready, reverse fields are probably
-        # unavailable, but try anyway.
             if not self.apps.ready:
-            try:
-                # Don't cache results
-                return self._get_fields_map()[field_name]
-            except KeyError:
                 raise FieldDoesNotExist(
                     "%s has no field named %r. The app cache isn't ready yet, "
-                    "so if this is an auto-created related field, it might not "
+                    "so if this is an auto-created related field, it won't "
                     "be available yet." % (self.object_name, field_name)
                 )
 
         try:
+            if m2m_in_kwargs:
+                # Previous API does not allow searching reverse fields.
+                raise FieldDoesNotExist('%s has no field named %r' % (self.object_name, field_name))
+
             # Retrieve field instance by name from cached or just-computed
             # field map.
             return self.fields_map[field_name]

tests/model_meta/tests.py

@@ -169,30 +169,24 @@ class GetFieldByNameTests(OptionsBaseTests):
         self.assertEqual(field_info[1:], (None, True, False))
         self.assertIsInstance(field_info[0], GenericRelation)
 
-    def test_get_fields_when_apps_not_ready(self):
+    def test_get_fields_only_searches_forward_on_apps_not_ready(self):
         opts = Person._meta
         # If apps registry is not ready, get_field() searches over only
         # forward fields.
         opts.apps.ready = False
-        # Clear cached data.
-        opts.__dict__.pop('fields_map', None)
         try:
             # 'data_abstract' is a forward field, and therefore will be found
             self.assertTrue(opts.get_field('data_abstract'))
             msg = (
-                "Person has no field named 'some_missing_field'. The app "
+                "Person has no field named 'relating_baseperson'. The app "
                 "cache isn't ready yet, so if this is an auto-created related "
-                "field, it might not be available yet."
+                "field, it won't be available yet."
             )
+            # 'data_abstract' is a reverse field, and will raise an exception
             with self.assertRaisesMessage(FieldDoesNotExist, msg):
-                opts.get_field('some_missing_field')
+                opts.get_field('relating_baseperson')
-            # Be sure it's not cached
-            self.assertNotIn('fields_map', opts.__dict__)
         finally:
             opts.apps.ready = True
-        # At this point searching a related field would cache fields_map
-        opts.get_field('relating_baseperson')
-        self.assertIn('fields_map', opts.__dict__)
 
 
 class RelationTreeTests(TestCase):