robertwb commented on code in PR #33432:
URL: https://github.com/apache/beam/pull/33432#discussion_r1894331690
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sdks/python/apache_beam/coders/coders.py:
##########
@@ -1039,11 +1039,16 @@ def __hash__(self):
@classmethod
def from_type_hint(cls, typehint, unused_registry):
- if issubclass(typehint, proto_utils.message_types):
+ # The typehint must be a subclass of google.protobuf.message.Message.
+ # ProtoCoder cannot work with message.Message itself, as required APIs are
+ # not implemented in the base class. If this occurs, an error is raised
Review Comment:
Perhaps clarify the issue a bit more, e.g.
ProtoCoder cannot work with message.Message itself, as deserialization of a
serialized proto requires knowledge of the desired concrete proto subclass
which is not stored in the encoded bytes themselves.
##########
sdks/python/apache_beam/coders/coders_test.py:
##########
@@ -86,6 +87,23 @@ def test_proto_coder(self):
self.assertEqual(ma, real_coder.decode(real_coder.encode(ma)))
self.assertEqual(ma.__class__, real_coder.to_type_hint())
+ def test_proto_coder_on_protobuf_message_subclasses(self):
+ # This replicates a scenario where users provide message.Message as the
+ # output typehint for a Map function, even though the actual output
messages
+ # are subclasses of message.Message.
+ ma = test_message.MessageA()
+ mb = ma.field2.add()
+ mb.field1 = True
+ ma.field1 = 'hello world'
+
+ coder = coders_registry.get_coder(message.Message)
+ # For messages of google.protobuf.message.Message, the fallback coder will
+ # be FastPrimitiveCoder other than ProtoCoder.
Review Comment:
...rather than ProtoCoder.
##########
sdks/python/apache_beam/coders/coders.py:
##########
@@ -1039,11 +1039,16 @@ def __hash__(self):
@classmethod
def from_type_hint(cls, typehint, unused_registry):
- if issubclass(typehint, proto_utils.message_types):
+ # The typehint must be a subclass of google.protobuf.message.Message.
Review Comment:
...a strict subclass...
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