From 5c7779e84ecd8e7b4f1e5b97e08dd1bd7b53386b Mon Sep 17 00:00:00 2001
From: Erik Nilsson <eriknil@live.com>
Date: Sun, 12 May 2019 19:34:33 -0400
Subject: [PATCH 1/2] added tests confirming the bug

---
 bigquery/tests/unit/test_table.py | 67 +++++++++++++++++++++++++++++++
 1 file changed, 67 insertions(+)

diff --git a/bigquery/tests/unit/test_table.py b/bigquery/tests/unit/test_table.py
index 07a625b98825..816ba4ec48da 100644
--- a/bigquery/tests/unit/test_table.py
+++ b/bigquery/tests/unit/test_table.py
@@ -1943,6 +1943,51 @@ def blocking_to_dataframe(*args, **kwargs):
         # Make sure that this test pushed to the progress queue.
         self.assertEqual(mock_queue().put_nowait.call_count, total_pages)
 
+    @unittest.skipIf(pandas is None, "Requires `pandas`")
+    @unittest.skipIf(
+        bigquery_storage_v1beta1 is None, "Requires `google-cloud-bigquery-storage`"
+    )
+    def test_to_dataframe_w_bqstorage_multiple_streams_return_unique_index(self):
+        from google.cloud.bigquery import schema
+        from google.cloud.bigquery import table as mut
+        from google.cloud.bigquery_storage_v1beta1 import reader
+
+        streams = [
+            {"name": "/projects/proj/dataset/dset/tables/tbl/streams/1234"},
+            {"name": "/projects/proj/dataset/dset/tables/tbl/streams/5678"},
+        ]
+        session = bigquery_storage_v1beta1.types.ReadSession(streams=streams)
+        session.avro_schema.schema = json.dumps({"fields": [{"name": "colA"}]})
+
+        bqstorage_client = mock.create_autospec(
+            bigquery_storage_v1beta1.BigQueryStorageClient)
+        bqstorage_client.create_read_session.return_value = session
+
+        mock_rowstream = mock.create_autospec(reader.ReadRowsStream)
+        bqstorage_client.read_rows.return_value = mock_rowstream
+
+        mock_rows = mock.create_autospec(reader.ReadRowsIterable)
+        mock_rowstream.rows.return_value = mock_rows
+
+        page_data_frame = pandas.DataFrame(
+            [{"colA": 1}, {"colA": -1}], columns=["colA"])
+        mock_page = mock.create_autospec(reader.ReadRowsPage)
+        mock_page.to_dataframe.return_value = page_data_frame
+        mock_pages = (mock_page, mock_page, mock_page)
+        type(mock_rows).pages = mock.PropertyMock(return_value=mock_pages)
+
+        row_iterator = self._make_one(
+            schema=[schema.SchemaField("colA", "IGNORED")],
+            table=mut.TableReference.from_string("proj.dset.tbl"),
+        )
+        got = row_iterator.to_dataframe(bqstorage_client=bqstorage_client)
+
+        self.assertEqual(list(got), ["colA"])
+        total_pages = len(streams) * len(mock_pages)
+        total_rows = len(page_data_frame) * total_pages
+        self.assertEqual(len(got.index), total_rows)
+        self.assertTrue(got.index.is_unique)
+
     @unittest.skipIf(pandas is None, "Requires `pandas`")
     @unittest.skipIf(
         bigquery_storage_v1beta1 is None, "Requires `google-cloud-bigquery-storage`"
@@ -2138,6 +2183,28 @@ def test_to_dataframe_w_bqstorage_fallback_to_tabledata_list(self):
         self.assertEqual(df.name.dtype.name, "object")
         self.assertEqual(df.age.dtype.name, "int64")
 
+    @unittest.skipIf(pandas is None, "Requires `pandas`")
+    @mock.patch("google.cloud.bigquery.table.RowIterator.pages",
+                new_callable=mock.PropertyMock)
+    def test_to_dataframe_tabledata_list_w_multiple_pages_return_unique_index(self, mock_pages):
+        from google.cloud.bigquery import schema
+
+        iterator_schema = [
+            schema.SchemaField("name", "STRING", mode="REQUIRED"),
+        ]
+        pages = [[{"name": "Bengt"}], [{"name": "Sven"}]]
+
+        mock_pages.return_value = pages
+        row_iterator = self._make_one(schema=iterator_schema)
+
+        df = row_iterator.to_dataframe(bqstorage_client=None)
+
+        self.assertIsInstance(df, pandas.DataFrame)
+        self.assertEqual(len(df), 2)
+        self.assertEqual(list(df), ["name"])
+        self.assertEqual(df.name.dtype.name, "object")
+        self.assertTrue(df.index.is_unique)
+
     @unittest.skipIf(pandas is None, "Requires `pandas`")
     @unittest.skipIf(
         bigquery_storage_v1beta1 is None, "Requires `google-cloud-bigquery-storage`"

From 54d7c4369e5165b5270e5899079083f9063ede62 Mon Sep 17 00:00:00 2001
From: Erik Nilsson <eriknil@live.com>
Date: Sun, 12 May 2019 19:38:04 -0400
Subject: [PATCH 2/2] reset index when concating data frames

---
 bigquery/google/cloud/bigquery/table.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/bigquery/google/cloud/bigquery/table.py b/bigquery/google/cloud/bigquery/table.py
index 864fff4458b1..1f9bb5eee3d4 100644
--- a/bigquery/google/cloud/bigquery/table.py
+++ b/bigquery/google/cloud/bigquery/table.py
@@ -1408,7 +1408,7 @@ def _to_dataframe_tabledata_list(self, dtypes, progress_bar=None):
             # Indicate that the download has finished.
             progress_bar.close()
 
-        return pandas.concat(frames)
+        return pandas.concat(frames, ignore_index=True)
 
     def _to_dataframe_bqstorage_stream(
         self, bqstorage_client, dtypes, columns, session, stream, worker_queue
@@ -1585,7 +1585,7 @@ def get_frames(pool):
 
         # Update the progress bar one last time to close it.
         self._process_progress_updates(progress_queue, progress_bar)
-        return pandas.concat(frames)
+        return pandas.concat(frames, ignore_index=True)
 
     def _get_progress_bar(self, progress_bar_type):
         """Construct a tqdm progress bar object, if tqdm is installed."""