feat: add prefer_bqstorage_client option for Connection

google/cloud/bigquery/dbapi/connection.py

@@ -35,12 +35,18 @@ class Connection(object):
             A client that uses the faster BigQuery Storage API to fetch rows from
             BigQuery. If not passed, it is created using the same credentials
             as ``client`` (provided that BigQuery Storage dependencies are installed).
-
-            If both clients are available, ``bqstorage_client`` is used for
-            fetching query results.
+        prefer_bqstorage_client (Optional[bool]):
+            Prefer the BigQuery Storage client over the REST client. If Storage
+            client isn't available, fall back to the REST client. Defaults to
+            ``True``.
     """
 
-    def __init__(self, client=None, bqstorage_client=None):
+    def __init__(
+        self,
+        client=None,
+        bqstorage_client=None,
+        prefer_bqstorage_client=True,
+    ):
         if client is None:
             client = bigquery.Client()
             self._owns_client = True
@@ -49,7 +55,10 @@ def __init__(self, client=None, bqstorage_client=None):
 
         # A warning is already raised by the BQ Storage client factory factory if
         # instantiation fails, or if the given BQ Storage client instance is outdated.
-        if bqstorage_client is None:
+        if not prefer_bqstorage_client:
+            bqstorage_client = None
+            self._owns_bqstorage_client = False
+        elif bqstorage_client is None:
             bqstorage_client = client._ensure_bqstorage_client()
             self._owns_bqstorage_client = bqstorage_client is not None
         else:
@@ -95,7 +104,7 @@ def cursor(self):
         return new_cursor
 
 
-def connect(client=None, bqstorage_client=None):
+def connect(client=None, bqstorage_client=None, prefer_bqstorage_client=True):
     """Construct a DB-API connection to Google BigQuery.
 
     Args:
@@ -108,11 +117,12 @@ def connect(client=None, bqstorage_client=None):
             A client that uses the faster BigQuery Storage API to fetch rows from
             BigQuery. If not passed, it is created using the same credentials
             as ``client`` (provided that BigQuery Storage dependencies are installed).
-
-            If both clients are available, ``bqstorage_client`` is used for
-            fetching query results.
+        prefer_bqstorage_client (Optional[bool]):
+            Prefer the BigQuery Storage client over the REST client. If Storage
+            client isn't available, fall back to the REST client. Defaults to
+            ``True``.
 
     Returns:
         google.cloud.bigquery.dbapi.Connection: A new DB-API connection to BigQuery.
     """
-    return Connection(client, bqstorage_client)
+    return Connection(client, bqstorage_client, prefer_bqstorage_client)

tests/unit/test_dbapi_connection.py

@@ -122,6 +122,26 @@ def test_connect_w_both_clients(self):
         self.assertIs(connection._client, mock_client)
         self.assertIs(connection._bqstorage_client, mock_bqstorage_client)
 
+    def test_connect_prefer_bqstorage_client_false(self):
+        pytest.importorskip("google.cloud.bigquery_storage")
+        from google.cloud.bigquery.dbapi import connect
+        from google.cloud.bigquery.dbapi import Connection
+
+        mock_client = self._mock_client()
+        mock_bqstorage_client = self._mock_bqstorage_client()
+        mock_client._ensure_bqstorage_client.return_value = mock_bqstorage_client
+
+        connection = connect(
+            client=mock_client,
+            bqstorage_client=mock_bqstorage_client,
+            prefer_bqstorage_client=False,
+        )
+
+        mock_client._ensure_bqstorage_client.assert_not_called()
+        self.assertIsInstance(connection, Connection)
+        self.assertIs(connection._client, mock_client)
+        self.assertIs(connection._bqstorage_client, None)
+
     def test_raises_error_if_closed(self):
         from google.cloud.bigquery.dbapi.exceptions import ProgrammingError