mongo-oplog2

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.
• Promise support which enables the use of async and await.
• The package has a very small footprint and requires just a few dependencies, including mongodb and eventemitter3.
• Uses eventemitter3 for high performance event emitting.
• Unit tested with mocha and built with typescript so bundled types are always up to date.
• Differences from mongo-oplog
  • does not attempt to support older versions of NodeJS; output Javascript targets es2016
  • does not have callback support for oplog operations (tail, stop, etc.)
  • built with typescript
  • use new to create an instance of MongoOplog or you can use the default export of createInstance which will do this for you
  • supports "pretty" format of emitted documents which conform to the style in mongo-trigger

Installation

$ npm install mongo-oplog2

Usage

import {MongoOplog, OplogDoc} from 'mongo-oplog2';
const oplog: MongoOplog = new MongoOplog('mongodb://127.0.0.1:27017/local', { ns: 'test.posts' });
 
oplog.tail();
 
oplog.on('op', (data: OplogDoc) => {
  console.log(data);
});
 
oplog.on('insert', (doc: OplogDoc) => {
  console.log(doc);
});
 
oplog.on('update', (doc: OplogDoc) => {
  console.log(doc);
});
 
oplog.on('delete', (doc: OplogDoc) => {
  console.log(doc.o._id);
});
 
oplog.on('error', (error: Error) => {
  console.log(error);
});
 
oplog.on('end', () => {
  console.log('Stream ended');
});
 
oplog.stop().then(() => {
  console.log('server stopped');
});

API

MongoOplog(uriOrDb, [options])

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

oplog.tail()

Start tailing. This method only supports Promise syntax.

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()

Stop tailing and disconnect from server. This method only supports Promise syntax.

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()

Destroy the mongo-oplog object by stop tailing and disconnecting from server. This method only supports Promise syntax.

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

Ignore incoming oplog events.

NOTE: This does not prevent the oplog itself from progressing the cursor. Any updates during the time between when you start ignoring and stop ignoring will not be sent to your application. The timestamp prior to start of ignore being set is preserved. If you really want to stop receiving events and then start receiving them again without loss you must use stop and tail instead of simply using ignore.

oplog.ignore = true; // to stop receiving events
oplog.ignore = false; // to resume receiving events

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

Ignore / resume filtered events.

NOTE: Ignoring events can easily result in missed events. See above.

filter.ignore = true; // to ignore events
filter.ignore = false; // to resume recepit of events

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:

Start MongoDB with:

$ mongod --replSet test

Start a mongo shell and configure mongo as follows:

$ mongo
> var config = {_id: "test", members: [{_id: 0, host: "127.0.0.1:27017"}]};
> rs.initiate(config);

Once configuration is initiated then you can run the test:

$ npm install
$ npm run test

Credits

This is a port of cayasso's mongo-oplog module to typescript, which guarantees types will always be up to date when using this package in your own TypeScript projects. Pretty document format is compatible with mongo-trigger.

License

(The MIT License)

Copyright (c) 2017 Jarom Loveridge

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.