Add unit tests for new QueryJob.to_dataframe() arguments.

bigquery/google/cloud/bigquery/table.py

@@ -1441,7 +1441,19 @@ class _EmptyRowIterator(object):
     pages = ()
     total_rows = 0
 
-    def to_dataframe(self):
+    def to_dataframe(self, bqstorage_client=None, dtypes=None):
+        """Create an empty dataframe.
+
+        Args:
+            bqstorage_client (Any):
+                Ignored. Added for compatibility with RowIterator.
+            dtypes (Any):
+                Ignored. Added for compatibility with RowIterator.
+
+        Returns:
+            pandas.DataFrame:
+                An empty :class:`~pandas.DataFrame`.
+        """
         if pandas is None:
             raise ValueError(_NO_PANDAS_ERROR)
         return pandas.DataFrame()

bigquery/tests/unit/test_job.py

@@ -13,6 +13,7 @@
 # limitations under the License.
 
 import copy
+import json
 import unittest
 
 import mock
@@ -22,6 +23,10 @@
     import pandas
 except (ImportError, AttributeError):  # pragma: NO COVER
     pandas = None
+try:
+    from google.cloud import bigquery_storage_v1beta1
+except (ImportError, AttributeError):  # pragma: NO COVER
+    bigquery_storage_v1beta1 = None
 
 
 def _make_credentials():
@@ -4543,6 +4548,114 @@ def test_to_dataframe(self):
         self.assertEqual(len(df), 4)  # verify the number of rows
         self.assertEqual(list(df), ["name", "age"])  # verify the column names
 
+    @unittest.skipIf(pandas is None, "Requires `pandas`")
+    def test_to_dataframe_ddl_query(self):
+        # Destination table may have no schema for some DDL and DML queries.
+        query_resource = {
+            "jobComplete": True,
+            "jobReference": {"projectId": self.PROJECT, "jobId": self.JOB_ID},
+            "schema": {"fields": []},
+        }
+        connection = _make_connection(query_resource)
+        client = _make_client(self.PROJECT, connection=connection)
+        resource = self._make_resource(ended=True)
+        job = self._get_target_class().from_api_repr(resource, client)
+
+        df = job.to_dataframe()
+
+        self.assertEqual(len(df), 0)
+
+    @unittest.skipIf(pandas is None, "Requires `pandas`")
+    @unittest.skipIf(
+        bigquery_storage_v1beta1 is None, "Requires `google-cloud-bigquery-storage`"
+    )
+    def test_to_dataframe_bqstorage(self):
+        query_resource = {
+            "jobComplete": True,
+            "jobReference": {"projectId": self.PROJECT, "jobId": self.JOB_ID},
+            "totalRows": "4",
+            "schema": {
+                "fields": [
+                    {"name": "name", "type": "STRING", "mode": "NULLABLE"},
+                    {"name": "age", "type": "INTEGER", "mode": "NULLABLE"},
+                ]
+            },
+        }
+        connection = _make_connection(query_resource)
+        client = _make_client(self.PROJECT, connection=connection)
+        resource = self._make_resource(ended=True)
+        job = self._get_target_class().from_api_repr(resource, client)
+        bqstorage_client = mock.create_autospec(
+            bigquery_storage_v1beta1.BigQueryStorageClient
+        )
+        session = bigquery_storage_v1beta1.types.ReadSession()
+        session.avro_schema.schema = json.dumps(
+            {
+                "type": "record",
+                "name": "__root__",
+                "fields": [
+                    {"name": "name", "type": ["null", "string"]},
+                    {"name": "age", "type": ["null", "long"]},
+                ],
+            }
+        )
+        bqstorage_client.create_read_session.return_value = session
+
+        job.to_dataframe(bqstorage_client=bqstorage_client)
+
+        bqstorage_client.create_read_session.assert_called_once_with(
+            mock.ANY, "projects/{}".format(self.PROJECT), read_options=mock.ANY
+        )
+
+    @unittest.skipIf(pandas is None, "Requires `pandas`")
+    def test_to_dataframe_column_dtypes(self):
+        begun_resource = self._make_resource()
+        query_resource = {
+            "jobComplete": True,
+            "jobReference": {"projectId": self.PROJECT, "jobId": self.JOB_ID},
+            "totalRows": "4",
+            "schema": {
+                "fields": [
+                    {"name": "start_timestamp", "type": "TIMESTAMP"},
+                    {"name": "seconds", "type": "INT64"},
+                    {"name": "miles", "type": "FLOAT64"},
+                    {"name": "km", "type": "FLOAT64"},
+                    {"name": "payment_type", "type": "STRING"},
+                    {"name": "complete", "type": "BOOL"},
+                    {"name": "date", "type": "DATE"},
+                ]
+            },
+        }
+        row_data = [
+            ["1.4338368E9", "420", "1.1", "1.77", "Cash", "true", "1999-12-01"],
+            ["1.3878117E9", "2580", "17.7", "28.5", "Cash", "false", "1953-06-14"],
+            ["1.3855653E9", "2280", "4.4", "7.1", "Credit", "true", "1981-11-04"],
+        ]
+        rows = [{"f": [{"v": field} for field in row]} for row in row_data]
+        query_resource["rows"] = rows
+        done_resource = copy.deepcopy(begun_resource)
+        done_resource["status"] = {"state": "DONE"}
+        connection = _make_connection(
+            begun_resource, query_resource, done_resource, query_resource
+        )
+        client = _make_client(project=self.PROJECT, connection=connection)
+        job = self._make_one(self.JOB_ID, self.QUERY, client)
+
+        df = job.to_dataframe(dtypes={"km": "float16"})
+
+        self.assertIsInstance(df, pandas.DataFrame)
+        self.assertEqual(len(df), 3)  # verify the number of rows
+        exp_columns = [field["name"] for field in query_resource["schema"]["fields"]]
+        self.assertEqual(list(df), exp_columns)  # verify the column names
+
+        self.assertEqual(df.start_timestamp.dtype.name, "datetime64[ns, UTC]")
+        self.assertEqual(df.seconds.dtype.name, "int64")
+        self.assertEqual(df.miles.dtype.name, "float64")
+        self.assertEqual(df.km.dtype.name, "float16")
+        self.assertEqual(df.payment_type.dtype.name, "object")
+        self.assertEqual(df.complete.dtype.name, "bool")
+        self.assertEqual(df.date.dtype.name, "object")
+
     def test_iter(self):
         import types