scovich commented on code in PR #8408: URL: https://github.com/apache/arrow-rs/pull/8408#discussion_r2376783290
########## parquet/src/arrow/schema/extension.rs: ########## @@ -0,0 +1,62 @@ +// Licensed to the Apache Software Foundation (ASF) under one +// or more contributor license agreements. See the NOTICE file +// distributed with this work for additional information +// regarding copyright ownership. The ASF licenses this file +// to you under the Apache License, Version 2.0 (the +// "License"); you may not use this file except in compliance +// with the License. You may obtain a copy of the License at +// +// http://www.apache.org/licenses/LICENSE-2.0 +// +// Unless required by applicable law or agreed to in writing, +// software distributed under the License is distributed on an +// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY +// KIND, either express or implied. See the License for the +// specific language governing permissions and limitations +// under the License. + +//! Arrow Extension Type Support for Parquet +//! +//! This module contains mapping code to map Parquet [`LogicalType`]s to/from +//! Arrow [`ExtensionType`]s. +//! +//! Extension types are represented using the metadata from Arrow [`Field`]s +//! with the key "ARROW:extension:name". + +use crate::basic::LogicalType; +use crate::schema::types::Type; +use arrow_schema::extension::ExtensionType; +use arrow_schema::Field; + +/// Adds extension type metadata, if necessary, based on the Parquet field's +/// [`LogicalType`] +/// +/// Some Parquet logical types, such as Variant, do not map directly to an +/// Arrow DataType, and instead are represented by an Arrow ExtensionType. +/// Extension types are attached to Arrow Fields via metadata. +pub(crate) fn add_extension_type(arrow_field: Field, parquet_type: &Type) -> Field { + let result = match parquet_type.get_basic_info().logical_type() { + #[cfg(feature = "variant_experimental")] + Some(LogicalType::Variant) => { + arrow_field.with_extension_type(parquet_variant_compute::VariantType) + } + // TODO add other LogicalTypes here + _ => arrow_field, + }; + result +} + +/// Return the Parquet logical type to use for the specified Arrow field, if any. +#[cfg(feature = "variant_experimental")] +pub(crate) fn logical_type_for_struct(field: &Field) -> Option<LogicalType> { + use parquet_variant_compute::VariantType; + if field.extension_type_name()? == VariantType::NAME { Review Comment: Can we do both? Check the name (= quick and cheap) and only `try_extension_type` if the name matches? (if they asked for Variant and provided an incorrect data type, they shouldn't be surprised at the cost of allocating an error message) -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
