[GitHub] [arrow] jorisvandenbossche commented on pull request #33955: GH-33954: [C++][Parquet] Preserve field-id for nested type

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

jorisvandenbossche commented on PR #33955:
URL: https://github.com/apache/arrow/pull/33955#issuecomment-1415969387

   > This looks good to me. @jorisvandenbossche Do you remember if there were any problems with Parquet field ids?
   
   I remember that we had previous PRs where we wondered what to do with it. Your comment at this PR summarizes how we currently handle it (https://github.com/apache/arrow/pull/10289#issuecomment-839634828):
   
   > Based on my understanding, it seems that we should:
   > * when reading from Parquet, reflect Parquet field_ids (if any) under the `PARQUET:field_id` metadata key
   > * when writing to Parquet, generate Parquet field_ids from the `PARQUET:field_id` metadata key (if present)
   > * not attempt to auto-generate any field_ids if they are not present in metadata
   
   So correctly preserving the field-ids for nested types seems to follow that. 
   
   @wgtmac the current test does a full roundtrip of the arrow<->parquet schemas, so I assume this indirectly also covers that we correctly write them to Parquet if the information is present in the field metadata of an Arrow schema?


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