feat: pass custom Client object to dbapi (#911)

Author: asthamohta

google/cloud/spanner_dbapi/connection.py

@@ -497,6 +497,7 @@ def connect(
     credentials=None,
     pool=None,
     user_agent=None,
+    client=None,
 ):
     """Creates a connection to a Google Cloud Spanner database.
 
@@ -529,25 +530,31 @@ def connect(
     :param user_agent: (Optional) User agent to be used with this connection's
                        requests.
 
+    :type client: Concrete subclass of
+                  :class:`~google.cloud.spanner_v1.Client`.
+    :param client: (Optional) Custom user provided Client Object
+
     :rtype: :class:`google.cloud.spanner_dbapi.connection.Connection`
     :returns: Connection object associated with the given Google Cloud Spanner
               resource.
     """
-
-    client_info = ClientInfo(
-        user_agent=user_agent or DEFAULT_USER_AGENT,
-        python_version=PY_VERSION,
-        client_library_version=spanner.__version__,
-    )
-
-    if isinstance(credentials, str):
-        client = spanner.Client.from_service_account_json(
-            credentials, project=project, client_info=client_info
+    if client is None:
+        client_info = ClientInfo(
+            user_agent=user_agent or DEFAULT_USER_AGENT,
+            python_version=PY_VERSION,
+            client_library_version=spanner.__version__,
         )
+        if isinstance(credentials, str):
+            client = spanner.Client.from_service_account_json(
+                credentials, project=project, client_info=client_info
+            )
+        else:
+            client = spanner.Client(
+                project=project, credentials=credentials, client_info=client_info
+            )
     else:
-        client = spanner.Client(
-            project=project, credentials=credentials, client_info=client_info
-        )
+        if project is not None and client.project != project:
+            raise ValueError("project in url does not match client object project")
 
     instance = client.instance(instance_id)
     conn = Connection(instance, instance.database(database_id, pool=pool))

tests/unit/spanner_dbapi/test_connection.py

@@ -18,6 +18,7 @@
 import mock
 import unittest
 import warnings
+import pytest
 
 PROJECT = "test-project"
 INSTANCE = "test-instance"
@@ -915,7 +916,52 @@ def test_request_priority(self):
             sql, params, param_types=param_types, request_options=None
         )
 
+    @mock.patch("google.cloud.spanner_v1.Client")
+    def test_custom_client_connection(self, mock_client):
+        from google.cloud.spanner_dbapi import connect
+
+        client = _Client()
+        connection = connect("test-instance", "test-database", client=client)
+        self.assertTrue(connection.instance._client == client)
+
+    @mock.patch("google.cloud.spanner_v1.Client")
+    def test_invalid_custom_client_connection(self, mock_client):
+        from google.cloud.spanner_dbapi import connect
+
+        client = _Client()
+        with pytest.raises(ValueError):
+            connect(
+                "test-instance",
+                "test-database",
+                project="invalid_project",
+                client=client,
+            )
+
 
 def exit_ctx_func(self, exc_type, exc_value, traceback):
     """Context __exit__ method mock."""
     pass
+
+
+class _Client(object):
+    def __init__(self, project="project_id"):
+        self.project = project
+        self.project_name = "projects/" + self.project
+
+    def instance(self, instance_id="instance_id"):
+        return _Instance(name=instance_id, client=self)
+
+
+class _Instance(object):
+    def __init__(self, name="instance_id", client=None):
+        self.name = name
+        self._client = client
+
+    def database(self, database_id="database_id", pool=None):
+        return _Database(database_id, pool)
+
+
+class _Database(object):
+    def __init__(self, database_id="database_id", pool=None):
+        self.name = database_id
+        self.pool = pool