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record-batch-writer

RecordBatchWriter​

This documentation reflects Arrow JS v4.0. Needs to be updated for the new Arrow API in v9.0 +.

The RecordBatchWriter "serializes" Arrow Tables (or streams of RecordBatches) to the Arrow File, Stream, or JSON representations for inter-process communication (see also: Arrow IPC format docs).

The RecordBatchWriter is conceptually a "transform" stream that transforms Tables or RecordBatches into binary Uint8Array chunks that represent the Arrow IPC messages (Schema, DictionaryBatch, RecordBatch, and in the case of the File format, Footer messages).

These binary chunks are buffered inside the RecordBatchWriter instance until they are consumed, typically by piping the RecordBatchWriter instance to a Writable Stream (like a file or socket), enumerating the chunks via async-iteration, or by calling toUint8Array() to create a single contiguous buffer of the concatenated results once the desired Tables or RecordBatches have been written.

RecordBatchWriter conforms to the AsyncIterableIterator protocol in all environments, and supports two additional stream primitives based on the environment (nodejs or browsers) available at runtime.

  • In nodejs, the RecordBatchWriter can be converted to a ReadableStream, piped to a WritableStream, and has a static method that returns a TransformStream suitable in chained pipe calls.
  • browser environments that support the DOM/WhatWG Streams Standard, corresponding methods exist to convert RecordBatchWriters to the DOM ReadableStream, WritableStream, and TransformStream variants.

Note: The Arrow JSON representation is not suitable as an IPC mechanism in real-world scenarios. It is used inside the Arrow project as a human-readable debugging tool and for validating interoperability between each language's separate implementation of the Arrow library.

Member Fields​

closed: Promise (readonly)

A Promise which resolves when this RecordBatchWriter is closed.

Static Methods​

RecordBatchWriter.throughNode(options?: Object): DuplexStream​

Creates a Node.js TransformStream that transforms an input ReadableStream of Tables or RecordBatches into a stream of Uint8Array Arrow Message chunks.

  • options.autoDestroy: boolean - (default: true) Indicates whether the RecordBatchWriter should close after writing the first logical stream of RecordBatches (batches which all share the same Schema), or should continue and reset each time it encounters a new Schema.
  • options.* - Any Node Duplex stream options can be supplied

Returns: A Node.js Duplex stream

Example:

const fs = require('fs');
const {PassThrough, finished} = require('stream');
const {Table, RecordBatchWriter} = require('apache-arrow');

const table = Table.new({
  i32: Int32Vector.from([1, 2, 3]),
  f32: Float32Vector.from([1.0, 1.5, 2.0])
});

const source = new PassThrough({objectMode: true});

const result = source
  .pipe(RecordBatchWriter.throughNode())
  .pipe(fs.createWriteStream('table.arrow'));

source.write(table);
source.end();

finished(result, () => console.log('done writing table.arrow'));

RecordBatchWriter.throughDOM(writableStrategy? : Object, readableStrategy? : Object) : Object​

Creates a DOM/WhatWG ReadableStream/WritableStream pair that together transforms an input ReadableStream of Tables or RecordBatches into a stream of Uint8Array Arrow Message chunks.

  • options.autoDestroy: boolean - (default: true) Indicates whether the RecordBatchWriter should close after writing the first logical stream of RecordBatches (batches which all share the same Schema), or should continue and reset each time it encounters a new Schema.
  • writableStrategy.*= - Any options for QueuingStrategy<RecordBatch>
  • readableStrategy.highWaterMark? : Number
  • readableStrategy.size?: Number

Returns: an object with the following fields:

  • writable: WritableStream<Table | RecordBatch>
  • readable: ReadableStream<Uint8Array>

Methods​

constructor(options? : Object)

  • options.autoDestroy: boolean -

toString(sync: Boolean): string | Promise<string>​

toUint8Array(sync: Boolean): Uint8Array | Promise<Uint8Array>​

writeAll(input: Table | Iterable<RecordBatch>): this​

writeAll(input: AsyncIterable<RecordBatch>): Promise<this>​

writeAll(input: PromiseLike<AsyncIterable<RecordBatch>>): Promise<this>​

writeAll(input: PromiseLike<Table | Iterable<RecordBatch>>): Promise<this>​

  • [Symbol.asyncIterator](): AsyncByteQueue<Uint8Array>

Returns An async iterator that produces Uint8Arrays.

toDOMStream(options?: Object): ReadableStream<Uint8Array>​

Returns a new DOM/WhatWG stream that can be used to read the Uint8Array chunks produced by the RecordBatchWriter

  • options - passed through to the DOM ReadableStream constructor, any DOM ReadableStream options.

toNodeStream(options?: Object): Readable​

  • options - passed through to the Node ReadableStream constructor, any Node ReadableStream options.

close() : void​

Close the RecordBatchWriter. After close is called, no more chunks can be written.

abort(reason?: any) : void​

finish() : this​

reset(sink?: WritableSink<ArrayBufferViewInput>, schema?: Schema | null): this​

Change the sink

write(payload?: Table | RecordBatch | Iterable<Table> | Iterable<RecordBatch> | null): void​

Writes a RecordBatch or all the RecordBatches from a Table.

Remarks​

  • Just like the RecordBatchReader, a RecordBatchWriter is a factory base class that returns an instance of the subclass appropriate to the situation: RecordBatchStreamWriter, RecordBatchFileWriter, RecordBatchJSONWriter