Those days are gone when people didn’t expect information for momentary access to data. Nowadays expectation everywhere is real-time action and result. Something is happened? not 1 day ago, not even 1 min ago but just now. Being notified constantly on any change of data points a bit critical from many application nowadays. So the upcoming MongoDB3.6 introduces a new $changeStream aggregation pipeline operator.

Change Stream:

Change streams are being implemented in the driver with a new aggregation operator, $changeStream and watch method in the API. Where able to specify a $change stage at the beginning of our pipeline and request that notifications are sent for specific changes or hooking something to a particular collection.

Change Streams in code:

var MongoClient = require('mongodb').MongoClient;
MongoClient.connect("mongodb://localhost:27017/myproject?readConcern=majority")
 .then(function(client){
   let db = client.db('myproject')
   // specific table for any change
   let change_streams = db.collection('documents').watch()
      change_streams.on('change', function(change){
        console.log(change);
      });
  });

// with aggregation on whole database

change_streams = client.db.collection.watch([
    {'$match': {
        'operationType': {'$in': ['insert']}
    }},
    {'$match': {
        'level': {'$lt': 350}
    }}
]);

for change inchange_streams:
    do_some_magic();

Note : If you are using node.js, you need to use following node module to get it working:

"dependencies": {
    "mongodb": "mongodb/node-mongodb-native#3.0.0"
 }

Change Stream action / operation Types:

• Insert
• Delete
• Replace (everything but the unique id)
• Update
• Invalidate (in cases of an invalid cursor being returned)

Thanks for reading, Happy coding :)