tustvold commented on code in PR #1682: URL: https://github.com/apache/arrow-rs/pull/1682#discussion_r869957607
########## parquet/src/arrow/schema/complex.rs: ########## @@ -0,0 +1,563 @@ +// 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 crate::arrow::schema::primitive::convert_primitive; +use crate::basic::{ConvertedType, Repetition}; +use crate::errors::ParquetError; +use crate::errors::Result; +use crate::schema::types::{SchemaDescriptor, Type, TypePtr}; +use arrow::datatypes::{DataType, Field, Schema}; + +fn get_repetition(t: &Type) -> Repetition { + let info = t.get_basic_info(); + match info.has_repetition() { + true => info.repetition(), + false => Repetition::REQUIRED, + } +} + +/// Representation of a parquet file, in terms of arrow schema elements +pub struct ParquetField { + pub rep_level: i16, + pub def_level: i16, + pub nullable: bool, + pub arrow_type: DataType, + pub field_type: ParquetFieldType, +} + +impl ParquetField { + fn into_list(self, name: &str) -> Self { + ParquetField { + rep_level: self.rep_level, + def_level: self.def_level, + nullable: false, + arrow_type: DataType::List(Box::new(Field::new( + name, + self.arrow_type.clone(), + false, + ))), + field_type: ParquetFieldType::Group { + children: vec![self], + }, + } + } + + pub fn children(&self) -> Option<&[ParquetField]> { + match &self.field_type { + ParquetFieldType::Primitive { .. } => None, + ParquetFieldType::Group { children } => Some(children), + } + } +} + +pub enum ParquetFieldType { + Primitive { + col_idx: usize, + primitive_type: TypePtr, + }, + Group { + children: Vec<ParquetField>, + }, +} + +struct VisitorContext { + rep_level: i16, + def_level: i16, + /// An optional [`DataType`] sourced from the embedded arrow schema + data_type: Option<DataType>, +} + +impl VisitorContext { + fn levels(&self, repetition: Repetition) -> (i16, i16, bool) { + match repetition { + Repetition::OPTIONAL => (self.def_level + 1, self.rep_level, true), + Repetition::REQUIRED => (self.def_level, self.rep_level, false), + Repetition::REPEATED => (self.def_level + 1, self.rep_level + 1, false), + } + } +} + +/// Walks the parquet schema in a depth-first fashion in order to extract the +/// necessary information to map it to arrow data structures +/// +/// See [Logical Types] for more information on the conversion algorithm +/// +/// [Logical Types]: https://github.com/apache/parquet-format/blob/master/LogicalTypes.md +struct Visitor { + /// The column index of the next leaf column + next_col_idx: usize, + + /// Mask of columns to include + column_mask: Vec<bool>, +} + +impl Visitor { + fn visit_primitive( + &mut self, + primitive_type: TypePtr, + context: VisitorContext, + ) -> Result<Option<ParquetField>> { + let col_idx = self.next_col_idx; + self.next_col_idx += 1; + + if !self.column_mask[col_idx] { + return Ok(None); + } + + let repetition = get_repetition(&primitive_type); + let (def_level, rep_level, nullable) = context.levels(repetition); + + let arrow_type = convert_primitive(&primitive_type, context.data_type)?; + + let primitive_field = ParquetField { + rep_level, + def_level, + nullable, + arrow_type, + field_type: ParquetFieldType::Primitive { + primitive_type: primitive_type.clone(), + col_idx, + }, + }; + + Ok(Some(match repetition { + Repetition::REPEATED => primitive_field.into_list(primitive_type.name()), Review Comment: Here is the logic to now support #1680, there is comprehensive test coverage of this in schema.rs, in particular test_arrow_schema_roundtrip. I'm actually quite pleased with this, despite the underlying list representation in parquet being fundamentally different, the ArrayBuilder can be completely oblivious to this fact :smile: -- 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: github-unsubscr...@arrow.apache.org For queries about this service, please contact Infrastructure at: us...@infra.apache.org
