raulcd commented on code in PR #53994:
URL: https://github.com/apache/arrow/pull/53994#discussion_r4312104252
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cpp/src/arrow/ipc/metadata_internal.cc:
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@@ -900,35 +953,21 @@ Status FieldFromFlatbuffer(const flatbuf::Field* field,
FieldPosition field_pos,
auto int_data = encoding->indexType();
CHECK_FLATBUFFERS_NOT_NULL(int_data, "DictionaryEncoding.indexType");
RETURN_NOT_OK(IntFromFlatbuffer(int_data, &index_type));
+ // The dictionary value type may be an extension type, whose metadata is
+ // found in DictionaryEncoding.custom_metadata (GH-49704)
+ if (encoding->custom_metadata() != nullptr) {
+ ARROW_ASSIGN_OR_RAISE(auto value_metadata,
+
internal::GetKeyValueMetadata(encoding->custom_metadata()));
+ RETURN_NOT_OK(MaybeDeserializeExtensionType(value_metadata.get(),
&type));
Review Comment:
I am wondering whether there would be a way of retaining this value_metadata
even if this is a not known extension type. So the reader could retain it and a
new writer would write it. I am thinking on the use case of data passing
through:
`app knows extension type` -> `app does not know extension type` -> `app
knows extension type`
Maybe not entirely related and just an implementation detail that can be
done as a follow up.
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