perf: use protobuf for metadata to reduce type conversions (#325)

* perf: use protobuf for metadata to reduce type conversions * fix: ensure the metadata return type remains the same * fix: only wrap non-None metadata pbs Co-authored-by: larkee <larkee@users.noreply.github.com>

Author: larkee

google/cloud/spanner_v1/_helpers.py

@@ -205,7 +205,7 @@ def _parse_value_pb(value_pb, field_type):
  _parse_value_pb(item_pb, field_type.struct_type.fields[i].type_)
  for (i, item_pb) in enumerate(value_pb.list_value.values)
  ]
- elif field_type.code == TypeCode.NUMERIC:
+ elif type_code == TypeCode.NUMERIC:
  return decimal.Decimal(value_pb.string_value)
  else:
  raise ValueError("Unknown type: %s" % (field_type,))

google/cloud/spanner_v1/streamed.py

@@ -18,6 +18,7 @@
 from google.protobuf.struct_pb2 import Value
 from google.cloud import exceptions
 from google.cloud.spanner_v1 import PartialResultSet
+from google.cloud.spanner_v1 import ResultSetMetadata
 from google.cloud.spanner_v1 import TypeCode
 import six
 
@@ -65,7 +66,9 @@ def metadata(self):
  :rtype: :class:`~google.cloud.spanner_v1.types.ResultSetMetadata`
  :returns: structure describing the results
  """
- return self._metadata
+ if self._metadata:
+ return ResultSetMetadata.wrap(self._metadata)
+ return None
 
  @property
  def stats(self):
@@ -119,7 +122,7 @@ def _consume_next(self):
  response_pb = PartialResultSet.pb(response)
 
  if self._metadata is None: # first response
- metadata = self._metadata = response.metadata
+ metadata = self._metadata = response_pb.metadata
 
  source = self._source
  if source is not None and source._transaction_id is None:

tests/unit/test_streamed.py

@@ -147,7 +147,7 @@ def test_properties_set(self):
  metadata = streamed._metadata = self._make_result_set_metadata(FIELDS)
  stats = streamed._stats = self._make_result_set_stats()
  self.assertEqual(list(streamed.fields), FIELDS)
- self.assertIs(streamed.metadata, metadata)
+ self.assertIs(streamed.metadata._pb, metadata)
  self.assertIs(streamed.stats, stats)
 
  def test__merge_chunk_bool(self):