Allow BigQuery to default on project name

plugins/bigquery/dbt/adapters/bigquery/connections.py

@@ -1,7 +1,8 @@
 from contextlib import contextmanager
 from dataclasses import dataclass
+from functools import lru_cache
 from requests.exceptions import ConnectionError
-from typing import Optional, Any, Dict
+from typing import Optional, Any, Dict, Tuple
 
 import google.auth
 import google.auth.exceptions
@@ -44,6 +45,16 @@
     ConnectionError,
 )
 
+@lru_cache()
+def get_bigquery_defaults() -> Tuple[Any, Optional[str]]:
+    """ 
+    Returns (credentials, project_id)
+
+    project_id where available from the environment 
+    """
+    # Cached, because the underlying implementation shells out, taking ~1s
+    return google.auth.default()
+
 
 class Priority(StrEnum):
     Interactive = 'interactive'
@@ -60,6 +71,9 @@ class BigQueryConnectionMethod(StrEnum):
 @dataclass
 class BigQueryCredentials(Credentials):
     method: BigQueryConnectionMethod
+    # BigQuery allows an empty database / project, where it defers to the
+    # environment for the project
+    database: Optional[str]
     timeout_seconds: Optional[int] = 300
     location: Optional[str] = None
     priority: Optional[Priority] = None
@@ -91,6 +105,16 @@ def _connection_keys(self):
         return ('method', 'database', 'schema', 'location', 'priority',
                 'timeout_seconds', 'maximum_bytes_billed')
 
+    def __post_init__(self):
+        # We need to inject the correct value of the database (aka project) at
+        # this stage, ref
+        # https://github.com/fishtown-analytics/dbt/pull/2908#discussion_r532927436.
+
+        # `database` is an alias of `project` in BigQuery
+        if self.database is None:
+            _, database = self.get_bigquery_defaults()
+            self.database = database
+
 
 class BigQueryConnectionManager(BaseConnectionManager):
     TYPE = 'bigquery'
@@ -170,7 +194,7 @@ def get_bigquery_credentials(cls, profile_credentials):
         creds = GoogleServiceAccountCredentials.Credentials
 
         if method == BigQueryConnectionMethod.OAUTH:
-            credentials, project_id = google.auth.default(scopes=cls.SCOPE)
+            credentials, _ = get_bigquery_defaults()
             return credentials
 
         elif method == BigQueryConnectionMethod.SERVICE_ACCOUNT:

test/unit/test_bigquery_adapter.py

@@ -96,6 +96,13 @@ def setUp(self):
                     'priority': 'batch',
                     'maximum_bytes_billed': 0,
                 },
+                'oauth--no-project': {
+                    'type': 'bigquery',
+                    'method': 'oauth',
+                    'schema': 'dummy_schema',
+                    'threads': 1,
+                    'location': 'Solar Station',
+                },
             },
             'target': 'oauth',
         }