change-stream-to-async-iterator

Turn any MongoDB ChangeStream into an async iterator.

GraphQL subscriptions expect to be passed an async iterator. Now you can turn any MongoDB ChangeStream into one. I hope it's useful for you!

Install

npm i -S change-stream-to-async-iterator

Usage

Quickstart

This is an example of a subscription resolver using graphql-yoga. It turns a ChangeStream that listens for insert operations on the items collection into an async iterator which the subscription resolver uses to push messages to the client through a WebSocket connection:

import changeStreamToAsyncIterator from 'change-stream-to-async-iterator';

const onCreateItem = {
  subscribe: (parent, args, context, info) =>
    changeStreamToAsyncIterator(context.db.collection('items'), [
      {
        $match: { operationType: 'insert' }
      }
    ], {
        fullDocument: true,
    }),
  resolve: payload => payload.fullDocument
};

export default {
  onCreateItem
};

This is another example using for-await...of:

(async function() {
    let asyncIterable = changeStreamToAsyncIterator(db.collection('items'), [
      {
        $match: { operationType: 'insert' }
      }
    ], {
        fullDocument: true,
    });

    for await (let data of asyncIterable) {
        console.log(data);
    }
})();

API

changeStreamToAsyncIterator(collection: Collection, pipeline: object[], options: ChangeStreamOptions & {startAtOperationTime?: Timestamp; session?: ClientSession;}): AsyncIterator<any>

Follow this link for documentation on colletion argument.

Follow this link to learn more about pipeline and options arguments.

License

Licensed under the MIT License, Copyright copyright 2019 Alfredo Quintero Tlacuilo. See LICENSE for more information.