Fixed #21783: (again) Found second source of bug, also squashed it.

django/db/migrations/operations/fields.py

@@ -27,7 +27,15 @@ class AddField(Operation):
         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.add_field(from_model, to_model._meta.get_field_by_name(self.name)[0])
+            field = to_model._meta.get_field_by_name(self.name)[0]
+            if not self.preserve_default:
+                field.default = self.field.default
+            schema_editor.add_field(
+                from_model,
+                field,
+            )
+            if not self.preserve_default:
+                field.default = NOT_PROVIDED
 
     def database_backwards(self, app_label, schema_editor, from_state, to_state):
         from_model = from_state.render().get_model(app_label, self.model_name)

tests/migrations/test_operations.py

@@ -184,6 +184,14 @@ class OperationTests(MigrationTestBase):
             if n == "height"
         ][0]
         self.assertEqual(field.default, NOT_PROVIDED)
+        # Test the database alteration
+        project_state.render().get_model("test_adflpd", "pony").objects.create(
+            weight = 4,
+        )
+        self.assertColumnNotExists("test_adflpd_pony", "height")
+        with connection.schema_editor() as editor:
+            operation.database_forwards("test_adflpd", editor, project_state, new_state)
+        self.assertColumnExists("test_adflpd_pony", "height")
 
     def test_add_field_m2m(self):
         """