arn4v / batch-mobile

Asynchronous batched iterable for (mongo) cursors. When one is not enough and all is too much.

batch-mobile 🦇

Asynchronous batched iterable for (mongo) cursors

A library when one is not enough and all is to much.

Installation

npm i batch-mobile

API

getBatchedIterableFromCursor(cursor, batchSize)

• cursor: Any iterable cursor which exposes an asynchronous next method (best practice with mongo is to create the cursor with the "batchSize" option to match the value passed in "batchSize" argument for optimal memory usage)
• batchSize: The size of the yielded batch. Defaults to 200 if unset.

Usage

Simple example

async function example() {
    const { getBatchedIterableFromCursor } = require('batch-mobile')
    for await (const batchOfItems of getBatchedIterableFromCursor(cursor)) {
      await pushBatchToService(batchOfItems)
    }
}();

Mongo example

const { MongoClient } = require('mongodb')
const client = await (new MongoClient(process.env.MONGO_URI)).connect()
const { getBatchedIterableFromCursor } = require('batch-mobile')

const BATCH_SIZE = 1000;
async function example() {
  try {
    const collection = client.db('application').collection('collection')
    // By using the batch size option we make sure mongo driver pulls
    // exactly the amount of documents into the process memory as we handle them.
    // This will cause optimal memory usage and prevent unnecessary round trips to the mongo
    // server
    const options = {cursor: {batchSize: BATCH_SIZE}}
    const cursor = collection
      .find({ foo: 'bar' }, options)
  
    for await (const batch of getBatchedIterableFromCursor(cursor, BATCH_SIZE)) {
      await processItemsFrom(batch)
    }
  } finally {
    await client.close(true)
  }
}();