[GitHub] [beam] Abacn commented on a diff in pull request #26059: Add a simple UnionCoder

["Abacn (via GitHub)" <gi...@apache.org>]

Abacn commented on code in PR #26059:
URL: https://github.com/apache/beam/pull/26059#discussion_r1172999641


##########
sdks/python/apache_beam/coders/union_coder_test.py:
##########
@@ -0,0 +1,61 @@
+#
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.
+# The ASF licenses this file to You under the Apache License, Version 2.0
+# (the "License"); you may not use this file except in compliance with
+# the License.  You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+# pytype: skip-file
+
+import logging
+import unittest
+
+from apache_beam.coders import coders
+from apache_beam.coders.union_coder import UnionCoder
+from apache_beam.coders.avro_record import AvroRecord
+
+
+class AvroTestCoder(coders.AvroGenericCoder):
+  SCHEMA = """
+  {
+    "type": "record", "name": "test",
+    "fields": [
+      {"name": "name", "type": "string"},
+      {"name": "age", "type": "int"}
+    ]
+  }
+  """
+
+  def __init__(self):
+    super().__init__(self.SCHEMA)
+
+
+class UnionCoderTest(unittest.TestCase):
+  def test_basics(self):
+
+    coder = UnionCoder([AvroTestCoder(), coders.BooleanCoder()])
+
+    self.assertEqual(coder.is_deterministic(), False)

Review Comment:
   Not obvious to me that why `is_deterministic()` gives false -- checked that this is because "AvroTestCoder" is false. (there is even a TODO(#19628) in AvroGenericCoder suggesting deterministic or not is not confirmed)
   
   If test deterministic we'd better have an independent test that feed both deterministic and non-deterministic test coders as test cases
   



##########
sdks/python/apache_beam/coders/union_coder.py:
##########
@@ -0,0 +1,84 @@
+#
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.
+# The ASF licenses this file to You under the Apache License, Version 2.0
+# (the "License"); you may not use this file except in compliance with
+# the License.  You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+# pytype: skip-file
+
+import struct
+
+from typing import Iterable
+
+from apache_beam.coders import Coder
+from apache_beam.coders.coders import FastCoder
+from apache_beam.typehints import typehints
+
+
+class UnionCoder(FastCoder):
+  def __init__(self, components):
+    # type: (Iterable[Coder]) -> None
+    if not components or not isinstance(components, list):
+      raise ValueError('A valid list of Coders must be provided.')
+
+    if len(components) > 255 or len(components) <= 1:
+      raise ValueError(
+          'The number of components for UnionCoder must be between 2 and 255.')
+
+    self._coders = components
+    self._coder_typehints = [c.to_type_hint() for c in self._coders]
+
+  def encode(self, value) -> bytes:
+    """
+        Encodes the given Union value into bytes.
+        """
+    typehint_type = type(value)
+    if typehint_type in self._coder_typehints:
+      coder_index = self._coder_typehints.index(typehint_type)

Review Comment:
   in operator and index both have O(n) complexity for list. Though usually Union should have only a few components, may consider make self._coder_typehints a map of {typeName(type): index(byte)} and just return `self._coder_typehints[typehint_type] + coder.encode(value)`



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