Node.js listen to MongoDB change

Question

Is there a way for Node.js to listen to a change in a particular data in a collection of MongoDB, and fire an event if a change happens?

Answer 1

Well, this is an old question, but I was struggling with the same thing. I found a number of tidbits that helped me put together a solution, and I've published it as a library:

https://github.com/TorchlightSoftware/mongo-watch

The library is written in coffeescript. Here's an example in javascript, for those that prefer.

var MongoWatch = require('mongo-watch'),
    watcher = new MongoWatch({parser: 'pretty'});

watcher.watch('test.users', function(event) {
  return console.log('something changed:', event);
});

Answer 2

MongoDB apparently now supports triggers and watch, this answer is outdated.

[Original] I believe you are looking for a database trigger.

Unfortunately, MongoDB has no support for them yet, so I don't think you can listen for changes directly from the database. You'll need to setup some sort of notification system (e.g. pub/sub) that alerts interested parties when a collection has changed.