Fix AlterField migrations that are related to a RenameModel migration

django/db/migrations/operations/fields.py

@@ -1,5 +1,6 @@
 from django.db import router
 from django.db.models.fields import NOT_PROVIDED
+from django.utils import six
 from .base import Operation
 
 
@@ -116,11 +117,17 @@ def database_forwards(self, app_label, schema_editor, from_state, to_state):
         from_model = from_state.render().get_model(app_label, self.model_name)
         to_model = to_state.render().get_model(app_label, self.model_name)
         if router.allow_migrate(schema_editor.connection.alias, to_model):
-            schema_editor.alter_field(
-                from_model,
-                from_model._meta.get_field_by_name(self.name)[0],
-                to_model._meta.get_field_by_name(self.name)[0],
-            )
+            from_field = from_model._meta.get_field_by_name(self.name)[0]
+            to_field = to_model._meta.get_field_by_name(self.name)[0]
+            # If the field is a relatedfield with an unresolved rel.to, just
+            # set it equal to the other field side. Bandaid fix for AlterField
+            # migrations that are part of a RenameModel change.
+            if from_field.rel and from_field.rel.to:
+                if isinstance(from_field.rel.to, six.string_types):
+                    from_field.rel.to = to_field.rel.to
+                elif isinstance(to_field.rel.to, six.string_types):
+                    to_field.rel.to = from_field.rel.to
+            schema_editor.alter_field(from_model, from_field, to_field)
 
     def database_backwards(self, app_label, schema_editor, from_state, to_state):
         self.database_forwards(app_label, schema_editor, from_state, to_state)

tests/migrations/test_operations.py

@@ -226,6 +226,47 @@ def test_rename_model(self):
         self.assertTableExists("test_dlmo_pony")
         self.assertTableNotExists("test_rnmo_horse")
 
+    def test_rename_model_with_related(self):
+        """
+        Tests the real-world combo of a RenameModel operation with AlterField
+        for a related field.
+        """
+        project_state = self.set_up_test_model(
+            "test_rnmowr", related_model=True)
+        # Test the state alterations
+        model_operation = migrations.RenameModel("Pony", "Horse")
+        new_state = project_state.clone()
+        model_operation.state_forwards("test_rnmowr", new_state)
+        self.assertNotIn(("test_rnmowr", "pony"), new_state.models)
+        self.assertIn(("test_rnmowr", "horse"), new_state.models)
+
+        self.assertEqual(
+            "Pony",
+            project_state.render().get_model("test_rnmowr", "rider")
+            ._meta.get_field_by_name("pony")[0].rel.to._meta.object_name)
+        field_operation = migrations.AlterField(
+            "Rider", "pony", models.ForeignKey("Horse"))
+        field_operation.state_forwards("test_rnmowr", new_state)
+        self.assertEqual(
+            "Horse",
+            new_state.render().get_model("test_rnmowr", "rider")
+            ._meta.get_field_by_name("pony")[0].rel.to._meta.object_name)
+
+        # Test the database alterations
+        self.assertTableExists("test_rnmowr_pony")
+        self.assertTableNotExists("test_rnmowr_horse")
+        with connection.schema_editor() as editor:
+            model_operation.database_forwards("test_rnmowr", editor, project_state, new_state)
+            field_operation.database_forwards("test_rnmowr", editor, project_state, new_state)
+        self.assertTableNotExists("test_rnmowr_pony")
+        self.assertTableExists("test_rnmowr_horse")
+        # And test reversal
+        with connection.schema_editor() as editor:
+            field_operation.database_backwards("test_rnmowr", editor, new_state, project_state)
+            model_operation.database_backwards("test_rnmowr", editor, new_state, project_state)
+        self.assertTableExists("test_rnmowr_pony")
+        self.assertTableNotExists("test_rnmowr_horse")
+
     def test_add_field(self):
         """
         Tests the AddField operation.