riodw/Mongodb_Data_Change.md

## Mongodb_Data_Change.md

      
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              Mongodb_Data_Change.md
            
          
    Check out this: Change Streams

January 10, 2018  - Release 3.6

https://docs.mongodb.com/v3.6/changeStreams/


It's new in mongodb 3.6
https://docs.mongodb.com/manual/release-notes/3.6/ 2018/01/10
$ mongod --version
db version v3.6.2


In order use changeStreams the database must be a Replication Set

More about Replication Sets:
https://docs.mongodb.com/manual/replication/

Your Database will be a "Standalone" by default.

How to Convert a Standalone to a Replica Set: https://docs.mongodb.com/manual/tutorial/convert-standalone-to-replica-set/


The following example is a practical application for how you might use this.


Specifically for Node.
/* file.js */
'use strict'


module.exports = function (
      app,
      io,
      User // Collection Name
) {
    // SET WATCH ON COLLECTION 
    const changeStream = User.watch();  

    // Socket Connection  
    io.on('connection', function (socket) {
        console.log('Connection!');

        // USERS - Change
        changeStream.on('change', function(change) {
            console.log('COLLECTION CHANGED');

            User.find({}, (err, data) => {
                if (err) throw err;
  
                if (data) {
                    // RESEND ALL USERS
                    socket.emit('users', data);
                }
            });
        });
    });
};
/* END - file.js */


Useful links:

https://docs.mongodb.com/manual/tutorial/convert-standalone-to-replica-set

https://docs.mongodb.com/manual/tutorial/change-streams-example

https://docs.mongodb.com/v3.6/tutorial/change-streams-example

http://plusnconsulting.com/post/MongoDB-Change-Streams