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

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

Author: Ilya Gurov

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)