[GitHub] [arrow] mapleFU commented on a diff in pull request #35146: GH-29781: [C++][Parquet] Switch to use compliant nested types by default

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

mapleFU commented on code in PR #35146:
URL: https://github.com/apache/arrow/pull/35146#discussion_r1191488592


##########
cpp/src/parquet/properties.h:
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@@ -938,13 +937,13 @@ class PARQUET_EXPORT ArrowWriterProperties {
     /// list types (default "item"), will use "entries", as is specified in

Review Comment:
   Oops.
   
   ```c++
   MapType::MapType(std::shared_ptr<DataType> key_type, std::shared_ptr<Field> item_field,
                    bool keys_sorted)
       : MapType(::arrow::field("key", std::move(key_type), false), std::move(item_field),
                 keys_sorted) {}
   
   MapType::MapType(std::shared_ptr<Field> key_field, std::shared_ptr<Field> item_field,
                    bool keys_sorted)
       : MapType(
             ::arrow::field("entries",
                            struct_({std::move(key_field), std::move(item_field)}), false),
             keys_sorted) {}
   ```
   
   Found `"entries"` in `arrow/type.cc`, and spec is using "element". 
   
   And here maybe we're using "entries":
   
   ```c++
   /// In a field with Map type, the field has a child Struct field, which then
   /// has two children: key type and the second the value type. The names of the
   /// child fields may be respectively "entries", "key", and "value", but this is
   /// not enforced.
   ///
   /// Map
   /// ```text
   ///   - child[0] entries: Struct
   ///     - child[0] key: K
   ///     - child[1] value: V
   /// ```
   /// Neither the "entries" field nor the "key" field may be nullable.
   ```
   
   According to spec. Map should use "key_value". Seems it's incorrect? Am I right?



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