read project_id from credentials if available (#258)

* read project_id from credentials if available

* Move project inference from credentials to shared GbqConnector

To more easily test the project ID inference, this commit also sends
the project ID as part of the query method call. Even though this is
redundant because the client object also contains the project ID, we
aren't exercising the bigquery.Client constructor in the unit tests to
avoid making real API calls.

Author: daureg

docs/source/changelog.rst

@@ -25,6 +25,8 @@ Enhancements
 - Allow ``table_schema`` in :func:`to_gbq` to contain only a subset of columns,
   with the rest being populated using the DataFrame dtypes (:issue:`218`) 
   (contributed by @johnpaton)
+- Read ``project_id`` in :func:`to_gbq` from provided ``credentials`` if
+  available (contributed by @daureg)
 
 .. _changelog-0.9.0:
 

pandas_gbq/gbq.py

@@ -318,6 +318,11 @@ def __init__(
         self.credentials = credentials
         default_project = None
 
+        # Service account credentials have a project associated with them.
+        # Prefer that project if none was supplied.
+        if self.project_id is None and hasattr(self.credentials, "project_id"):
+            self.project_id = credentials.project_id
+
         # Load credentials from cache.
         if not self.credentials:
             self.credentials = context.credentials
@@ -421,6 +426,7 @@ def run_query(self, query, **kwargs):
                 query,
                 job_config=bigquery.QueryJobConfig.from_api_repr(job_config),
                 location=self.location,
+                project=self.project_id,
             )
             logger.debug("Query running...")
         except (RefreshError, ValueError):

tests/unit/test_gbq.py

@@ -47,6 +47,27 @@ def mock_get_credentials(*args, **kwargs):
     return mock_credentials, "default-project"
 
 
+@pytest.fixture
+def mock_service_account_credentials():
+    import google.oauth2.service_account
+
+    mock_credentials = mock.create_autospec(
+        google.oauth2.service_account.Credentials
+    )
+    return mock_credentials
+
+
+@pytest.fixture
+def mock_compute_engine_credentials():
+    import google.auth.compute_engine
+
+    mock_credentials = mock.create_autospec(
+        google.auth.compute_engine.Credentials
+    )
+    return mock_credentials
+
+
+@pytest.fixture
 def mock_get_user_credentials(*args, **kwargs):
     import google.auth.credentials
 
@@ -260,6 +281,36 @@ def test_read_gbq_with_inferred_project_id(monkeypatch):
     assert df is not None
 
 
+def test_read_gbq_with_inferred_project_id_from_service_account_credentials(
+    mock_bigquery_client, mock_service_account_credentials
+):
+    mock_service_account_credentials.project_id = "service_account_project_id"
+    df = gbq.read_gbq(
+        "SELECT 1",
+        dialect="standard",
+        credentials=mock_service_account_credentials,
+    )
+    assert df is not None
+    mock_bigquery_client.query.assert_called_once_with(
+        "SELECT 1",
+        job_config=mock.ANY,
+        location=None,
+        project="service_account_project_id",
+    )
+
+
+def test_read_gbq_without_inferred_project_id_from_compute_engine_credentials(
+    mock_compute_engine_credentials
+):
+    with pytest.raises(ValueError) as exception:
+        gbq.read_gbq(
+            "SELECT 1",
+            dialect="standard",
+            credentials=mock_compute_engine_credentials,
+        )
+    assert "Could not determine project ID" in str(exception)
+
+
 def test_read_gbq_with_invalid_private_key_json_should_fail():
     with pytest.raises(pandas_gbq.exceptions.InvalidPrivateKeyFormat):
         gbq.read_gbq(