[GitHub] [arrow] houqp commented on a change in pull request #9256: WIP: ARROW-11310: [Rust] implement JSON writer

[GitBox <gi...@apache.org>]

houqp commented on a change in pull request #9256:
URL: https://github.com/apache/arrow/pull/9256#discussion_r564283209



##########
File path: rust/arrow/src/json/writer.rs
##########
@@ -0,0 +1,301 @@
+// 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 set_column_by_primitive_type<T: ArrowPrimitiveType>(
+    rows: &mut [JsonMap<String, Value>],
+    row_count: usize,
+    array: &ArrayRef,
+    col_name: &str,
+) {
+    let primitive_arr = as_primitive_array::<T>(array);
+    for (i, row) in rows.iter_mut().enumerate().take(row_count) {
+        row.insert(
+            col_name.to_string(),
+            primitive_arr
+                .value(i)

Review comment:
       Good catch, will update the code and add test cases.




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