scovich commented on code in PR #7921: URL: https://github.com/apache/arrow-rs/pull/7921#discussion_r2204684924
########## parquet-variant-compute/src/shredding.rs: ########## @@ -0,0 +1,364 @@ +// 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. + +use arrow_schema::{ArrowError, DataType, Fields}; + +// Keywords defined by the shredding spec +pub const METADATA: &str = "metadata"; +pub const VALUE: &str = "value"; +pub const TYPED_VALUE: &str = "typed_value"; + +pub fn validate_value_and_typed_value( + fields: &Fields, + allow_both_null: bool, +) -> Result<(), ArrowError> { + let value_field_res = fields.iter().find(|f| f.name() == VALUE); + let typed_value_field_res = fields.iter().find(|f| f.name() == TYPED_VALUE); + + if !allow_both_null { + if let (None, None) = (value_field_res, typed_value_field_res) { + return Err(ArrowError::InvalidArgumentError( + "Invalid VariantArray: StructArray must contain either `value` or `typed_value` fields or both.".to_string() + )); + } + } + + if let Some(value_field) = value_field_res { + // if !value_field.is_nullable() { + // return Err(ArrowError::InvalidArgumentError( + // "Expected value field to be nullable".to_string(), + // )); + // } Review Comment: What I don't know, is what should happen with `metadata` in a variant that shredded as a deeply nested struct, where one or more of those struct fields happen to be variant typed (which in turn can also be shredded further, and which can _also_ contain variant fields of their own? ``` v: VARIANT { metadata: BINARY, value: BINARY, typed_value: { a: STRUCT { b: STRUCT { c: STRUCT { w: VARIANT { metadata: BINARY, << --- ??? value: BINARY, typed_value: STRUCT { x: STRUCT { y: STRUCT { z: STRUCT { u: VARIANT { metadata: BINARY, <<--- ??? value: BINARY, } } } } } } } } } } } ``` The [spec](https://github.com/apache/parquet-format/blob/master/VariantShredding.md#variant-metadata) says that > Variant metadata is stored in the top-level Variant group in a binary metadata column regardless of whether the Variant value is shredded. > > All value columns within the Variant must use the same metadata. All field names of a Variant, whether shredded or not, must be present in the metadata. I'm pretty sure that means `w` and `u` must _not_ have `metadata` columns -- because they are still "inside" `v`. Even if one tried to store path names of `u` inside all three `metadata` columns, the field ids would disagree unless we forced `u.metadata` and `w.metadata` to be copies of `v.metadata`. Easy enough to do that in arrow-rs (all array data are anyway Arc), but what about the actual parquet file?? ########## parquet-variant-compute/src/shredding.rs: ########## @@ -0,0 +1,364 @@ +// 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. + +use arrow_schema::{ArrowError, DataType, Fields}; + +// Keywords defined by the shredding spec +pub const METADATA: &str = "metadata"; +pub const VALUE: &str = "value"; +pub const TYPED_VALUE: &str = "typed_value"; + +pub fn validate_value_and_typed_value( + fields: &Fields, + allow_both_null: bool, +) -> Result<(), ArrowError> { + let value_field_res = fields.iter().find(|f| f.name() == VALUE); + let typed_value_field_res = fields.iter().find(|f| f.name() == TYPED_VALUE); + + if !allow_both_null { + if let (None, None) = (value_field_res, typed_value_field_res) { + return Err(ArrowError::InvalidArgumentError( + "Invalid VariantArray: StructArray must contain either `value` or `typed_value` fields or both.".to_string() + )); + } + } + + if let Some(value_field) = value_field_res { + // if !value_field.is_nullable() { + // return Err(ArrowError::InvalidArgumentError( + // "Expected value field to be nullable".to_string(), + // )); + // } Review Comment: Spec [says](https://github.com/apache/parquet-format/blob/master/VariantShredding.md#value-shredding) that both can be nullable: > ``` > required group measurement (VARIANT) { > required binary metadata; > optional binary value; > optional int64 typed_value; > } > ``` -- This is an automated message from the Apache Git Service. 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