houqp commented on a change in pull request #9256: URL: https://github.com/apache/arrow/pull/9256#discussion_r568340019
########## File path: rust/arrow/src/json/writer.rs ########## @@ -0,0 +1,635 @@ +// 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. + +//! JSON Writer +//! +//! This JSON writer allows converting Arrow record batches into array of JSON objects. It also +//! provides a Writer struct to help serialize record batches directly into line-delimited JSON +//! objects as bytes. +//! +//! Serialize record batches into array of JSON objects: +//! +//! ``` +//! use std::sync::Arc; +//! +//! use arrow::array::Int32Array; +//! use arrow::datatypes::{DataType, Field, Schema}; +//! use arrow::json; +//! use arrow::record_batch::RecordBatch; +//! +//! let schema = Schema::new(vec![Field::new("a", DataType::Int32, false)]); +//! let a = Int32Array::from(vec![1, 2, 3]); +//! let batch = RecordBatch::try_new(Arc::new(schema), vec![Arc::new(a)]).unwrap(); +//! +//! let json_rows = json::writer::record_batches_to_json_rows(&[batch]); +//! assert_eq!( +//! serde_json::Value::Object(json_rows[1].clone()), +//! serde_json::json!({"a": 2}), +//! ); +//! ``` +//! +//! Serialize record batches into line-delimited JSON bytes: +//! +//! ``` +//! use std::sync::Arc; +//! +//! use arrow::array::Int32Array; +//! use arrow::datatypes::{DataType, Field, Schema}; +//! use arrow::json; +//! use arrow::record_batch::RecordBatch; +//! +//! let schema = Schema::new(vec![Field::new("a", DataType::Int32, false)]); +//! let a = Int32Array::from(vec![1, 2, 3]); +//! let batch = RecordBatch::try_new(Arc::new(schema), vec![Arc::new(a)]).unwrap(); +//! +//! let buf = Vec::new(); +//! let mut writer = json::Writer::new(buf); +//! writer.write_batches(&vec![batch]).unwrap(); +//! ``` + +use std::io::{BufWriter, Write}; +use std::iter; + +use serde_json::map::Map as JsonMap; +use serde_json::Value; + +use crate::array::*; +use crate::datatypes::*; +use crate::error::Result; +use crate::record_batch::RecordBatch; + +fn primitive_array_to_json<T: ArrowPrimitiveType>(array: &ArrayRef) -> Vec<Value> { + as_primitive_array::<T>(array) + .iter() + .map(|maybe_value| match maybe_value { + Some(v) => v.into_json_value().unwrap_or(Value::Null), + None => Value::Null, + }) + .collect() +} + +fn struct_array_to_jsonmap_array( + array: &StructArray, + row_count: usize, +) -> Vec<JsonMap<String, Value>> { + let inner_col_names = array.column_names(); + + let mut inner_objs = iter::repeat(JsonMap::new()) + .take(row_count) + .collect::<Vec<JsonMap<String, Value>>>(); + + array + .columns() + .iter() + .enumerate() + .for_each(|(j, struct_col)| { + set_column_for_json_rows( + &mut inner_objs, + row_count, + struct_col, + inner_col_names[j], + ); + }); + + inner_objs +} + +pub fn array_to_json_array(array: &ArrayRef) -> Vec<Value> { + match array.data_type() { + DataType::Null => iter::repeat(Value::Null).take(array.len()).collect(), + DataType::Boolean => as_boolean_array(array) + .iter() + .map(|maybe_value| match maybe_value { + Some(v) => v.into(), + None => Value::Null, + }) + .collect(), + + DataType::Utf8 => as_string_array(array) + .iter() + .map(|maybe_value| match maybe_value { + Some(v) => v.into(), + None => Value::Null, + }) + .collect(), + DataType::Int8 => primitive_array_to_json::<Int8Type>(array), + DataType::Int16 => primitive_array_to_json::<Int16Type>(array), + DataType::Int32 => primitive_array_to_json::<Int32Type>(array), + DataType::Int64 => primitive_array_to_json::<Int64Type>(array), + DataType::UInt8 => primitive_array_to_json::<UInt8Type>(array), + DataType::UInt16 => primitive_array_to_json::<UInt16Type>(array), + DataType::UInt32 => primitive_array_to_json::<UInt32Type>(array), + DataType::UInt64 => primitive_array_to_json::<UInt64Type>(array), + DataType::Float32 => primitive_array_to_json::<Float32Type>(array), + DataType::Float64 => primitive_array_to_json::<Float64Type>(array), + DataType::List(_) => as_list_array(array) + .iter() + .map(|maybe_value| match maybe_value { + Some(v) => Value::Array(array_to_json_array(&v)), + None => Value::Null, + }) + .collect(), + DataType::Struct(_) => { + let jsonmaps = + struct_array_to_jsonmap_array(as_struct_array(array), array.len()); + jsonmaps.into_iter().map(Value::Object).collect() + } + _ => { Review comment: yeah, i was planning to add dictionary support, but this patch set already grew larger than I expected, so I decided to leave that to a follow up PR for easier review. ---------------------------------------------------------------- This is an automated message from the Apache Git Service. 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