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 <[email protected]>

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):