README.md

mongo-oplog

Listening to MongoDB live changes using oplog.

Features

• Support start and stop tailing the MongoDB oplog at any time.
• Support filtering oplog events by namespaces (database and collections).
• Built on top of the native NodeJS MongoDB driver.
• First class Promise support which enable the use of async and await.
• The package has a very small footprint and requires just a few dependencies including mongodb, debug and eventemitter3.
• Uses eventemitter3 for high performance event emitting.
• Strict and readable code enforced with xo
• Unit tested with mocha and built with babel for backward compatibility with older versions of NodeJS like v6.x and v7.x.

IMPORTANT! Major update version 2.0.x

2.0.x is a major rewrite taking advantage of es6 and adding support for promises and async/await. Callbacks are still supported for backward compatibility. This version has minimum API changes, but these changes might affect your code, so please take a look at the upgrading guide before installing.

Check the upgrading guide here

Go here for the old 1.x readme

Go here for the old 0.x readme

Installation

$ npm install mongo-oplog

Configure MongoDB with replica set

You need to configure your MongoDB instance (local instance) to have access to the oplog, here are some quick steps on how to do so:

1. Shutdown your existing mongo instance if its running.

2. Restart the instance. Use the --replSet option to specify the name of the replica set.

$ sudo mongod --replSet rs0

3. Connect to the mongo instance by executing mongo in your terminal:

$ mongo

4. In the mongo shell run rs.initiate() to initiate the new replica set:

> rs.initiate()

Once it is initiated then you are ready to start using mongo-oplog.

And here is the official MongoDB documentation if you need additional help on MongoDB replica set.

Usage

import MongoOplog from 'mongo-oplog'
const oplog = MongoOplog('mongodb://127.0.0.1:27017/local', { ns: 'test.posts' })

oplog.tail();

oplog.on('op', data => {
  console.log(data);
});

oplog.on('insert', doc => {
  console.log(doc);
});

oplog.on('update', doc => {
  console.log(doc);
});

oplog.on('delete', doc => {
  console.log(doc.o._id);
});

oplog.on('error', error => {
  console.log(error);
});

oplog.on('end', () => {
  console.log('Stream ended');
});

oplog.stop(() => {
  console.log('server stopped');
});

API

MongoOplog(uri, [options])

• uri: Valid MongoDB uri or a MongoDB server instance.
• options MongoDB connection options.

oplog.tail([fn])

Start tailing. This method support both Promise and callback.

oplog.tail().then(() => {
  console.log('tailing started')
}).catch(err => console.error(err))

// or with async/await
async function tail() {
  try {
    await oplog.tail()
    console.log('tailing started')
  } catch (err) {
    console.log(err)
  }
}

oplog.stop([fn])

Stop tailing and disconnect from server. This method support both Promise and callback.

oplog.stop().then(() => {
  console.log('tailing stopped')
}).catch(err => console.error(err))

// or with async/await
async function stop() {
  try {
    await oplog.stop()
    console.log('tailing stopped')
  } catch (err) {
    console.log(err)
  }
}

oplog.destroy([fn])

Destroy the mongo-oplog object by stop tailing and disconnecting from server. This method support both Promise and callback.

oplog.destroy.then(() => {
  console.log('destroyed')
}).catch(err => console.error(err))

// or with async/await
async function destroy() {
  try {
    await oplog.destroy()
    console.log('destroyed')
  } catch (err) {
    console.log(err)
  }
}

oplog.ignore

Pause and resume oplog events.

oplog.ignore = true; // to pause
oplog.ignore = false // to resume

oplog.filter(ns)

Create and return a filter object.

const filter = oplog.filter('*.posts')
filter.on('op', fn)
oplog.tail()

filter.destroy()

Destroy filter object.

filter.destroy()

filter.ignore

Pause and resume filter events.

filter.ignore = true; // to pause
filter.ignore = false // to resume

events

Events supported by oplog and filter;

• op: All bellow operations (oplog/filter).
• insert: Document insert (oplog/filter).
• update: Document update (oplog/filter).
• delete: Document delete (oplog/filter).
• end: Cursor stream ended (oplog).
• error: Error (oplog).

Run tests

Configure MongoDB for active oplog, once this is done then you can run the test:

$ npm install
$ npm run test

License

(The MIT License)

Copyright (c) 2015 Jonathan Brumley <cayasso@gmail.com>

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the 'Software'), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.