alamb commented on code in PR #8408: URL: https://github.com/apache/arrow-rs/pull/8408#discussion_r2382796418
########## parquet/src/arrow/schema/extension.rs: ########## @@ -0,0 +1,68 @@ +// 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; + // Check the name (= quick and cheap) and only try_extension_type if the name matches + // to avoid unnecessary String allocations in ArrowError + if field.extension_type_name()? != VariantType::NAME { + return None; + } + match field.try_extension_type::<VariantType>() { + Ok(VariantType) => Some(LogicalType::Variant), + // Given check above, this should not error, but if it does ignore + Err(_e) => None, + } Review Comment: Yeah, I think it is a fine line to decide how much of the canonical extension types end up in the core parquet/Arrow API Including them all by default makes the initial developer experience nicer perhaps and keeps the code cleaner, but it makes it harder to customize the binary size / feature set In my mind I am trying to follow the existing pattern / guidelines (set by @tustvold I think) and I do think it makes sense, but I do understand there are tradeoffs involved ########## parquet/src/arrow/schema/extension.rs: ########## @@ -0,0 +1,68 @@ +// 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; + // Check the name (= quick and cheap) and only try_extension_type if the name matches + // to avoid unnecessary String allocations in ArrowError Review Comment: I filed a ticket: - https://github.com/apache/arrow-rs/issues/8474 And made a PR with some more examples: - https://github.com/apache/arrow-rs/pull/8475 -- This is an automated message from the Apache Git Service. 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