Module arrow::json::writer[−][src]

Expand description

JSON Writer

This JSON writer converts Arrow RecordBatches into arrays of JSON objects or JSON formatted byte streams.

Writing JSON Objects

To serialize RecordBatches into array of JSON objects, use record_batches_to_json_rows:

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}),
);

Writing JSON formatted byte streams

To serialize RecordBatches into line-delimited JSON bytes, use LineDelimitedWriter:

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();

// Write the record batch out as JSON
let buf = Vec::new();
let mut writer = json::LineDelimitedWriter::new(buf);
writer.write_batches(&vec![batch]).unwrap();
writer.finish().unwrap();

// Get the underlying buffer back,
let buf = writer.into_inner();
assert_eq!(r#"{"a":1}
{"a":2}
{"a":3}
"#, String::from_utf8(buf).unwrap())

To serialize RecordBatches into a well formed JSON array, use ArrayWriter:

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();

// Write the record batch out as a JSON array
let buf = Vec::new();
let mut writer = json::ArrayWriter::new(buf);
writer.write_batches(&vec![batch]).unwrap();
writer.finish().unwrap();

// Get the underlying buffer back,
let buf = writer.into_inner();
assert_eq!(r#"[{"a":1},{"a":2},{"a":3}]"#, String::from_utf8(buf).unwrap())

Structs

JsonArray	Produces JSON output as a single JSON array. For example
LineDelimited	Produces JSON output with one record per line. For example
Writer	A JSON writer which serializes `RecordBatch`es to a stream of `u8` encoded JSON objects. See the module level documentation for detailed usage and examples. The specific format of the stream is controlled by the `JsonFormat` type parameter.

Traits

JsonFormat

This trait defines how to format a sequence of JSON objects to a byte stream.

Functions

array_to_json_array	Converts an arrow `ArrayRef` into a `Vec` of Serde JSON `serde_json::Value`’s
record_batches_to_json_rows	Converts an arrow `RecordBatch` into a `Vec` of Serde JSON `JsonMap`s (objects)

Type Definitions

ArrayWriter	A JSON writer which serializes `RecordBatch`es to JSON arrays
LineDelimitedWriter	A JSON writer which serializes `RecordBatch`es to newline delimited JSON objects