[GitHub] [arrow] jorisvandenbossche commented on a change in pull request #6959: ARROW-5649: [Integration][C++] Create integration test for extension types

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jorisvandenbossche commented on a change in pull request #6959:
URL: https://github.com/apache/arrow/pull/6959#discussion_r413750283



##########
File path: python/pyarrow/tests/test_extension_type.py
##########
@@ -445,22 +445,28 @@ def test_parquet(tmpdir, registered_period_type):
     import base64
     decoded_schema = base64.b64decode(meta.metadata[b"ARROW:schema"])
     schema = pa.ipc.read_schema(pa.BufferReader(decoded_schema))
-    assert schema.field("ext").metadata == {
-        b'ARROW:extension:metadata': b'freq=D',
-        b'ARROW:extension:name': b'pandas.period'}
+    # Since the type could be reconstructed, the extension type metadata is
+    # absent.
+    assert schema.field("ext").metadata == {}

Review comment:
       I don't have a fully good sense of what people do with this metadata, but I suppose when the type was recognized, it should not be a problem if the metadata is not present anymore (since you can always retrieve it again from the type instance).
   
   I know Micah mentioned they were using those metadata in BigQuery, but without a registered extension type, so such use case should not be impacted.
   
   This test is for parquet roundtrip, but a similar change was done for plain IPC roundtrip as well? (that currently also preserves the field metadata, even when the type was recognized)




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