feat(db_api): make rowcount property NotImplemented (#603)

Co-authored-by: larkee <31196561+larkee@users.noreply.github.com>

google/cloud/spanner_dbapi/cursor.py

@@ -44,8 +44,6 @@
 
 from google.rpc.code_pb2 import ABORTED, OK
 
-_UNSET_COUNT = -1
-
 ColumnDetails = namedtuple("column_details", ["null_ok", "spanner_type"])
 Statement = namedtuple("Statement", "sql, params, param_types, checksum, is_insert")
 
@@ -60,7 +58,6 @@ class Cursor(object):
     def __init__(self, connection):
         self._itr = None
         self._result_set = None
-        self._row_count = _UNSET_COUNT
         self.lastrowid = None
         self.connection = connection
         self._is_closed = False
@@ -119,12 +116,15 @@ def description(self):
 
     @property
     def rowcount(self):
-        """The number of rows produced by the last `.execute()`.
+        """The number of rows produced by the last `execute()` call.
 
-        :rtype: int
-        :returns: The number of rows produced by the last .execute*().
+        :raises: :class:`NotImplemented`.
         """
-        return self._row_count
+        raise NotImplementedError(
+            "The `rowcount` property is non-operational. Request "
+            "resulting rows are streamed by the `fetch*()` methods "
+            "and can't be counted before they are all streamed."
+        )
 
     def _raise_if_closed(self):
         """Raise an exception if this cursor is closed.
@@ -153,11 +153,7 @@ def _do_execute_update(self, transaction, sql, params):
         result = transaction.execute_update(
             sql, params=params, param_types=get_param_types(params)
         )
-        self._itr = None
-        if type(result) == int:
-            self._row_count = result
-
-        return result
+        self._itr = iter([result])
 
     def _do_batch_update(self, transaction, statements, many_result_set):
         status, res = transaction.batch_update(statements)
@@ -421,9 +417,6 @@ def _handle_DQL_with_snapshot(self, snapshot, sql, params):
         # Read the first element so that the StreamedResultSet can
         # return the metadata after a DQL statement. See issue #155.
         self._itr = PeekIterator(self._result_set)
-        # Unfortunately, Spanner doesn't seem to send back
-        # information about the number of rows available.
-        self._row_count = _UNSET_COUNT
 
     def _handle_DQL(self, sql, params):
         if self.connection.read_only and not self.connection.autocommit:

tests/unit/spanner_dbapi/test_cursor.py

@@ -62,11 +62,10 @@ def test_property_description(self):
         self.assertIsInstance(cursor.description[0], ColumnInfo)
 
     def test_property_rowcount(self):
-        from google.cloud.spanner_dbapi.cursor import _UNSET_COUNT
-
         connection = self._make_connection(self.INSTANCE, self.DATABASE)
         cursor = self._make_one(connection)
-        self.assertEqual(cursor.rowcount, _UNSET_COUNT)
+        with self.assertRaises(NotImplementedError):
+            cursor.rowcount
 
     def test_callproc(self):
         from google.cloud.spanner_dbapi.exceptions import InterfaceError
@@ -94,26 +93,25 @@ def test_close(self, mock_client):
             cursor.execute("SELECT * FROM database")
 
     def test_do_execute_update(self):
-        from google.cloud.spanner_dbapi.cursor import _UNSET_COUNT
+        from google.cloud.spanner_dbapi.checksum import ResultsChecksum
 
         connection = self._make_connection(self.INSTANCE, self.DATABASE)
         cursor = self._make_one(connection)
+        cursor._checksum = ResultsChecksum()
         transaction = mock.MagicMock()
 
         def run_helper(ret_value):
             transaction.execute_update.return_value = ret_value
-            res = cursor._do_execute_update(
+            cursor._do_execute_update(
                 transaction=transaction, sql="SELECT * WHERE true", params={},
             )
-            return res
+            return cursor.fetchall()
 
         expected = "good"
-        self.assertEqual(run_helper(expected), expected)
-        self.assertEqual(cursor._row_count, _UNSET_COUNT)
+        self.assertEqual(run_helper(expected), [expected])
 
         expected = 1234
-        self.assertEqual(run_helper(expected), expected)
-        self.assertEqual(cursor._row_count, expected)
+        self.assertEqual(run_helper(expected), [expected])
 
     def test_execute_programming_error(self):
         from google.cloud.spanner_dbapi.exceptions import ProgrammingError
@@ -706,7 +704,6 @@ def test_setoutputsize(self):
 
     def test_handle_dql(self):
         from google.cloud.spanner_dbapi import utils
-        from google.cloud.spanner_dbapi.cursor import _UNSET_COUNT
 
         connection = self._make_connection(self.INSTANCE, mock.MagicMock())
         connection.database.snapshot.return_value.__enter__.return_value = (
@@ -718,7 +715,6 @@ def test_handle_dql(self):
         cursor._handle_DQL("sql", params=None)
         self.assertEqual(cursor._result_set, ["0"])
         self.assertIsInstance(cursor._itr, utils.PeekIterator)
-        self.assertEqual(cursor._row_count, _UNSET_COUNT)
 
     def test_context(self):
         connection = self._make_connection(self.INSTANCE, self.DATABASE)