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new f2b4e34d71 GH-49456: [C++] Use static key/item/value field names for
map type again (#49457)
f2b4e34d71 is described below
commit f2b4e34d71996d744efe037bc2927e7658e78c33
Author: Sutou Kouhei <[email protected]>
AuthorDate: Thu Mar 5 20:04:21 2026 +0900
GH-49456: [C++] Use static key/item/value field names for map type again
(#49457)
### Rationale for this change
This reverts GH-49415 because the previous behavior (using static
"key"/"value"/"entries" field names for map type) is better. Our specification
defines the static field names.
### What changes are included in this PR?
Always use "key"/"value"/"entries" for map type field names.
### Are these changes tested?
Yes.
### Are there any user-facing changes?
No. This just revers the unreleased change.
* GitHub Issue: #49456
Authored-by: Sutou Kouhei <[email protected]>
Signed-off-by: Raúl Cumplido <[email protected]>
---
cpp/src/arrow/ipc/metadata_internal.cc | 15 ++++++++++++++-
1 file changed, 14 insertions(+), 1 deletion(-)
diff --git a/cpp/src/arrow/ipc/metadata_internal.cc
b/cpp/src/arrow/ipc/metadata_internal.cc
index 68dfaa0798..7f2a47b069 100644
--- a/cpp/src/arrow/ipc/metadata_internal.cc
+++ b/cpp/src/arrow/ipc/metadata_internal.cc
@@ -390,7 +390,20 @@ Status ConcreteTypeFromFlatbuffer(flatbuf::Type type,
const void* type_data,
return Status::Invalid("Map's keys must be non-nullable");
} else {
auto map = static_cast<const flatbuf::Map*>(type_data);
- *out = std::make_shared<MapType>(children[0], map->keysSorted());
+ // We always use "key"/"value"/"entries" field names instead
+ // of field names in FlatBuffers because the specification
+ // defines them:
+ //
+ //
https://github.com/apache/arrow/blob/apache-arrow-23.0.1/format/Schema.fbs#L127-L130
+ //
+ // In a field with Map type, the field has a child Struct
+ // field, which then has two children: the key type and the
+ // value type. The names of the child fields may be
+ // respectively "entries", "key", and "value", but this is
+ // not enforced.
+ *out =
std::make_shared<MapType>(children[0]->type()->field(0)->WithName("key"),
+
children[0]->type()->field(1)->WithName("value"),
+ map->keysSorted());
}
return Status::OK();
case flatbuf::Type::Type_FixedSizeList:
