Make total_rows available on RowIterator before iteration (#7622)

* Make total_rows available on RowIterator before iteration

After running a query, the total number of rows is available from the
call to the getQueryResults API. This commit plumbs the total rows
through to the faux Table created in QueryJob.results and then on
through to the RowIterator created by list_rows.

* Simplify RowIterator constructor. Add test comments.

Use getattr instead of protecting with hasattr in the RowIterator
constructor.

Add comments about intentionally conflicting values for total_rows.

bigquery/docs/snippets.py

@@ -1908,8 +1908,7 @@ def test_client_query_total_rows(client, capsys):
         location="US",
     )  # API request - starts the query
 
-    results = query_job.result()  # Waits for query to complete.
-    next(iter(results))  # Fetch the first page of results, which contains total_rows.
+    results = query_job.result()  # Wait for query to complete.
     print("Got {} rows.".format(results.total_rows))
     # [END bigquery_query_total_rows]
 

bigquery/google/cloud/bigquery/job.py

@@ -2835,6 +2835,7 @@ def result(self, timeout=None, retry=DEFAULT_RETRY):
         schema = self._query_results.schema
         dest_table_ref = self.destination
         dest_table = Table(dest_table_ref, schema=schema)
+        dest_table._properties["numRows"] = self._query_results.total_rows
         return self._client.list_rows(dest_table, retry=retry)
 
     def to_dataframe(self, bqstorage_client=None, dtypes=None, progress_bar_type=None):

bigquery/google/cloud/bigquery/table.py

@@ -1308,13 +1308,13 @@ def __init__(
             page_start=_rows_page_start,
             next_token="pageToken",
         )
-        self._schema = schema
         self._field_to_index = _helpers._field_to_index_mapping(schema)
-        self._total_rows = None
         self._page_size = page_size
-        self._table = table
-        self._selected_fields = selected_fields
         self._project = client.project
+        self._schema = schema
+        self._selected_fields = selected_fields
+        self._table = table
+        self._total_rows = getattr(table, "num_rows", None)
 
     def _get_next_page_response(self):
         """Requests the next page from the path provided.

bigquery/tests/unit/test_client.py

@@ -4359,18 +4359,21 @@ def test_list_rows_empty_table(self):
         client._connection = _make_connection(response, response)
 
         # Table that has no schema because it's an empty table.
-        rows = tuple(
-            client.list_rows(
-                # Test with using a string for the table ID.
-                "{}.{}.{}".format(
-                    self.TABLE_REF.project,
-                    self.TABLE_REF.dataset_id,
-                    self.TABLE_REF.table_id,
-                ),
-                selected_fields=[],
-            )
+        rows = client.list_rows(
+            # Test with using a string for the table ID.
+            "{}.{}.{}".format(
+                self.TABLE_REF.project,
+                self.TABLE_REF.dataset_id,
+                self.TABLE_REF.table_id,
+            ),
+            selected_fields=[],
         )
-        self.assertEqual(rows, ())
+
+        # When a table reference / string and selected_fields is provided,
+        # total_rows can't be populated until iteration starts.
+        self.assertIsNone(rows.total_rows)
+        self.assertEqual(tuple(rows), ())
+        self.assertEqual(rows.total_rows, 0)
 
     def test_list_rows_query_params(self):
         from google.cloud.bigquery.table import Table, SchemaField
@@ -4573,7 +4576,7 @@ def test_list_rows_with_missing_schema(self):
 
             conn.api_request.assert_called_once_with(method="GET", path=table_path)
             conn.api_request.reset_mock()
-            self.assertIsNone(row_iter.total_rows, msg=repr(table))
+            self.assertEqual(row_iter.total_rows, 2, msg=repr(table))
 
             rows = list(row_iter)
             conn.api_request.assert_called_once_with(

bigquery/tests/unit/test_job.py

@@ -4024,21 +4024,41 @@ def test_estimated_bytes_processed(self):
         self.assertEqual(job.estimated_bytes_processed, est_bytes)
 
     def test_result(self):
+        from google.cloud.bigquery.table import RowIterator
+
         query_resource = {
             "jobComplete": True,
             "jobReference": {"projectId": self.PROJECT, "jobId": self.JOB_ID},
             "schema": {"fields": [{"name": "col1", "type": "STRING"}]},
+            "totalRows": "2",
         }
-        connection = _make_connection(query_resource, query_resource)
+        tabledata_resource = {
+            # Explicitly set totalRows to be different from the query response.
+            # to test update during iteration.
+            "totalRows": "1",
+            "pageToken": None,
+            "rows": [{"f": [{"v": "abc"}]}],
+        }
+        connection = _make_connection(query_resource, tabledata_resource)
         client = _make_client(self.PROJECT, connection=connection)
         resource = self._make_resource(ended=True)
         job = self._get_target_class().from_api_repr(resource, client)
 
         result = job.result()
 
-        self.assertEqual(list(result), [])
+        self.assertIsInstance(result, RowIterator)
+        self.assertEqual(result.total_rows, 2)
+
+        rows = list(result)
+        self.assertEqual(len(rows), 1)
+        self.assertEqual(rows[0].col1, "abc")
+        # Test that the total_rows property has changed during iteration, based
+        # on the response from tabledata.list.
+        self.assertEqual(result.total_rows, 1)
 
     def test_result_w_empty_schema(self):
+        from google.cloud.bigquery.table import _EmptyRowIterator
+
         # Destination table may have no schema for some DDL and DML queries.
         query_resource = {
             "jobComplete": True,
@@ -4052,6 +4072,7 @@ def test_result_w_empty_schema(self):
 
         result = job.result()
 
+        self.assertIsInstance(result, _EmptyRowIterator)
         self.assertEqual(list(result), [])
 
     def test_result_invokes_begins(self):