fix(spanner-django): db_returning should only be overridden for Spanner (#16111)

The db_returning attribute of AutoFields should only be overridden for
Spanner database connections, and not globally for all databases.

Note: Many tests are failing. These failures are not due to these
changes, but due to existing failures for this library.

Fixes #15930

Replaces googleapis/python-spanner-django#961

Author: olavloite

packages/django-google-spanner/django_spanner/__init__.py

@@ -84,19 +84,15 @@ def autofield_init(self, *args, **kwargs):
             == "true"
         ):
             self.default = gen_rand_int64
+            self.db_returning = False
+            self.validators = []
             break
 
 
 AutoField.__init__ = autofield_init
-AutoField.db_returning = False
-AutoField.validators = []
 
 SmallAutoField.__init__ = autofield_init
 BigAutoField.__init__ = autofield_init
-SmallAutoField.db_returning = False
-BigAutoField.db_returning = False
-SmallAutoField.validators = []
-BigAutoField.validators = []
 
 
 def get_prep_value(self, value):

packages/django-google-spanner/tests/unit/django_spanner/test_schema.py

@@ -408,19 +408,27 @@ def test_autofield_no_default(self):
         """Spanner, default is not provided."""
         field = AutoField(name="field_name")
         assert gen_rand_int64 == field.default
+        # db_returning must be explicitly False because Spanner is handling ID generation client-side
+        assert getattr(field, "db_returning", True) is False
 
     def test_autofield_default(self):
         """Spanner, default provided."""
         mock_func = mock.Mock()
         field = AutoField(name="field_name", default=mock_func)
         assert gen_rand_int64 != field.default
         assert mock_func == field.default
+        # A default was already provided, so Spanner does not generate random IDs client-side.
+        # Therefore, db_returning does not need to be overridden to False.
+        assert field.db_returning is True
 
     def test_autofield_not_spanner(self):
         """Not Spanner, default not provided."""
         connection.settings_dict["ENGINE"] = "another_db"
         field = AutoField(name="field_name")
         assert gen_rand_int64 != field.default
+        # db_returning should remain untouched (implicitly True) for non-Spanner databases
+        # so that Django retrieves the auto-increment ID correctly.
+        assert field.db_returning is True
         connection.settings_dict["ENGINE"] = "django_spanner"
 
     def test_autofield_not_spanner_w_default(self):
@@ -430,6 +438,8 @@ def test_autofield_not_spanner_w_default(self):
         field = AutoField(name="field_name", default=mock_func)
         assert gen_rand_int64 != field.default
         assert mock_func == field.default
+        # Because it's not a Spanner database, the behavior shouldn't be altered in any way.
+        assert field.db_returning is True
         connection.settings_dict["ENGINE"] = "django_spanner"
 
     def test_autofield_spanner_as_non_default_db_random_generation_enabled(
@@ -441,6 +451,9 @@ def test_autofield_spanner_as_non_default_db_random_generation_enabled(
         connections.settings["secondary"]["RANDOM_ID_GENERATION_ENABLED"] = "true"
         field = AutoField(name="field_name")
         assert gen_rand_int64 == field.default
+        # Since this specific connection explicitly enables client-side random generation,
+        # we must tell Django not to attempt retrieving the DB's returned ID.
+        assert getattr(field, "db_returning", True) is False
         connections.settings["default"]["ENGINE"] = "django_spanner"
         connections.settings["secondary"]["ENGINE"] = "django_spanner"
         del connections.settings["secondary"]["RANDOM_ID_GENERATION_ENABLED"]
@@ -450,4 +463,7 @@ def test_autofield_random_generation_disabled(self):
         connections.settings["default"]["RANDOM_ID_GENERATION_ENABLED"] = "false"
         field = AutoField(name="field_name")
         assert gen_rand_int64 != field.default
+        # Because we're delegating ID generation back to the database backend,
+        # Django needs to be able to retrieve the assigned ID.
+        assert field.db_returning is True
         del connections.settings["default"]["RANDOM_ID_GENERATION_ENABLED"]