chore: introduce configuration option for id generation

Adds a configuration option for enabling/disabling client-side ID generation
using a random UUID. This allows users to better control ID generation when
using non-Spanner databases in combination with Spanner.

This option can in the future also be used for using IDENTITY columns for
ID generation.

Author: olavloite

django_spanner/__init__.py

@@ -12,8 +12,11 @@
 # do that.
 from uuid import uuid4
 
+RANDOM_ID_GENERATION_ENABLED_SETTING = "RANDOM_ID_GENERATION_ENABLED"
+
 import pkg_resources
 from django.conf.global_settings import DATABASES
+from django.db import DEFAULT_DB_ALIAS
 from google.cloud.spanner_v1 import JsonObject
 from django.db.models.fields import (
     NOT_PROVIDED,
@@ -65,12 +68,22 @@ def autofield_init(self, *args, **kwargs):
     kwargs["blank"] = True
     Field.__init__(self, *args, **kwargs)
 
+    # The following behavior is chosen to prevent breaking changes with the original behavior.
+    # 1. We use a client-side randomly generated int64 value for autofields if Spanner is the
+    #    default database, and DISABLE_RANDOM_ID_GENERATION has not been set.
+    # 2. If Spanner is one of the non-default databases, and no value at all has been set for
+    #    DISABLE_RANDOM_ID_GENERATION, then we do not enable it. If there is a value for this
+    #    configuration option, then we use that value.
     databases = django.db.connections.databases
     for db, config in databases.items():
+        default_enabled = str(db == DEFAULT_DB_ALIAS)
         if (
             config["ENGINE"] == "django_spanner"
             and self.default == NOT_PROVIDED
-            and not config.get("DISABLE_RANDOM_ID_GENERATION", "false").lower() == "true"
+            and config.get(
+                RANDOM_ID_GENERATION_ENABLED_SETTING, default_enabled
+            ).lower()
+            == "true"
         ):
             self.default = gen_rand_int64
             break

tests/mockserver_tests/mock_server_test_base.py

@@ -181,7 +181,9 @@ def teardown_class(cls):
     def setup_method(self, test_method):
         for db, config in DATABASES.items():
             if config["ENGINE"] == "django_spanner":
-                connections[db].settings_dict["OPTIONS"]["client"] = self.client
+                connections[db].settings_dict["OPTIONS"][
+                    "client"
+                ] = self.client
                 connections[db].settings_dict["OPTIONS"]["pool"] = self.pool
 
     def teardown_method(self, test_method):

tests/mockserver_tests/test_basics.py

@@ -13,12 +13,14 @@
 # limitations under the License.
 from google.cloud.spanner_v1 import (
     BatchCreateSessionsRequest,
-    ExecuteSqlRequest, CommitRequest,
+    ExecuteSqlRequest,
+    CommitRequest,
 )
 from tests.mockserver_tests.mock_server_test_base import (
     MockServerTestBase,
     add_select1_result,
-    add_singer_query_result, add_update_count,
+    add_singer_query_result,
+    add_update_count,
 )
 from django.db import connection, models
 
@@ -77,7 +79,8 @@ def test_insert_singer(self):
             "INSERT INTO tests_singer "
             "(id, first_name, last_name) "
             "VALUES (@a0, @a1, @a2)",
-            1)
+            1,
+        )
         singer = Singer(first_name="test", last_name="test")
         singer.save()
         requests = self.spanner_service.requests
@@ -107,7 +110,8 @@ class LocalSinger(models.Model):
                 "INSERT INTO tests_localsinger "
                 "(first_name, last_name) "
                 "VALUES (@a0, @a1)",
-                1)
+                1,
+            )
             singer = LocalSinger(first_name="test", last_name="test")
             singer.save()
             requests = self.spanner_service.requests

tests/unit/django_spanner/test_schema.py

@@ -6,7 +6,7 @@
 
 
 from .models import Author
-from django.db import NotSupportedError, connection
+from django.db import NotSupportedError, connection, connections
 from django.db.models import Index
 from django.db.models.fields import AutoField, IntegerField
 from django_spanner import gen_rand_int64
@@ -433,3 +433,27 @@ def test_autofield_not_spanner_w_default(self):
         assert gen_rand_int64 != field.default
         assert mock_func == field.default
         connection.settings_dict["ENGINE"] = "django_spanner"
+
+    def test_autofield_spanner_as_non_default_db_random_generation_enabled(
+        self,
+    ):
+        """Not Spanner as the default db, default for field not provided."""
+        connections.settings["default"]["ENGINE"] = "another_db"
+        connections.settings["secondary"]["ENGINE"] = "django_spanner"
+        connections.settings["secondary"][
+            "RANDOM_ID_GENERATION_ENABLED"
+        ] = "true"
+        field = AutoField(name="field_name")
+        assert gen_rand_int64 == field.default
+        connections.settings["default"]["ENGINE"] = "django_spanner"
+        connections.settings["secondary"]["ENGINE"] = "django_spanner"
+        del connections.settings["secondary"]["RANDOM_ID_GENERATION_ENABLED"]
+
+    def test_autofield_random_generation_disabled(self):
+        """Spanner, default is not provided."""
+        connections.settings["default"][
+            "RANDOM_ID_GENERATION_ENABLED"
+        ] = "false"
+        field = AutoField(name="field_name")
+        assert gen_rand_int64 != field.default
+        del connections.settings["default"]["RANDOM_ID_GENERATION_ENABLED"]