[3.0.x] Refs #30798 -- Prevented chaining fields from the same related model multiple times in model Meta.ordering.

Backport of c7944628a1 from master

django/db/models/base.py

@@ -1711,6 +1711,8 @@ class Model(metaclass=ModelBase):
                     fld = _cls._meta.get_field(part)
                     if fld.is_relation:
                         _cls = fld.get_path_info()[-1].to_opts.model
+                    else:
+                        _cls = None
                 except (FieldDoesNotExist, AttributeError):
                     if fld is None or fld.get_transform(part) is None:
                         errors.append(

tests/invalid_models_tests/test_models.py

@@ -814,6 +814,26 @@ class OtherModelTests(SimpleTestCase):
             )
         ])
 
+    def test_ordering_pointing_multiple_times_to_model_fields(self):
+        class Parent(models.Model):
+            field1 = models.CharField(max_length=100)
+            field2 = models.CharField(max_length=100)
+
+        class Child(models.Model):
+            parent = models.ForeignKey(Parent, models.CASCADE)
+
+            class Meta:
+                ordering = ('parent__field1__field2',)
+
+        self.assertEqual(Child.check(), [
+            Error(
+                "'ordering' refers to the nonexistent field, related field, "
+                "or lookup 'parent__field1__field2'.",
+                obj=Child,
+                id='models.E015',
+            )
+        ])
+
     def test_ordering_allows_registered_lookups(self):
         class Model(models.Model):
             test = models.CharField(max_length=100)