paleolimbot opened a new issue, #44714:
URL: https://github.com/apache/arrow/issues/44714
### Describe the bug, including details regarding any error messages,
version, and platform.
When Map types are received via the C Data interface, field metadata
(including extension metadata) is dropped. This seems unintentional given that
we maintain that metadata for a list of structs:
```python
import duckdb
duckdb_cursor = duckdb.connect()
duckdb_cursor.execute("SET arrow_lossless_conversion = true")
arrow_table = duckdb_cursor.execute("select map {uuid(): 1::uhugeint,
uuid(): 2::uhugeint} as li").arrow()
res = duckdb_cursor.execute("select typeof(li) FROM arrow_table").fetchall()
print ("map type")
print (arrow_table.schema)
print (res)
# map type
# li: map<fixed_size_binary[16], fixed_size_binary[16]>
# child 0, entries: struct<key: fixed_size_binary[16] not null, value:
fixed_size_binary[16]> not null
# child 0, key: fixed_size_binary[16] not null
# child 1, value: fixed_size_binary[16]
# [('MAP(BLOB, BLOB)',)]
arrow_table = duckdb_cursor.execute("select [{'keys': uuid(), 'values':
uuid()}] as li").arrow()
res = duckdb_cursor.execute("select typeof(li) FROM arrow_table").fetchall()
print ("fixed size list type")
print (arrow_table.schema)
print (res)
# map type
# li: list<l: struct<keys: fixed_size_binary[16], values:
fixed_size_binary[16]>>
# child 0, l: struct<keys: fixed_size_binary[16], values:
fixed_size_binary[16]>
# child 0, keys: fixed_size_binary[16]
# -- field metadata --
# ARROW:extension:metadata: ''
# ARROW:extension:name: 'arrow.uuid'
# child 1, values: fixed_size_binary[16]
# -- field metadata --
# ARROW:extension:metadata: ''
# ARROW:extension:name: 'arrow.uuid'
# [('STRUCT(keys UUID, "values" UUID)[]',)]
```
This occurs because we reconstruct the fields to canonicalize the field
names:
https://github.com/apache/arrow/blob/d7bc3788ea2773399b7ef489438c725999bfa83d/cpp/src/arrow/c/bridge.cc#L1298-L1321
I think that we don't have that problem in the IPC type conversion:
https://github.com/apache/arrow/blob/d7bc3788ea2773399b7ef489438c725999bfa83d/cpp/src/arrow/ipc/metadata_internal.cc#L393-L395
### Component(s)
C++
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