How do I subscribe to a model instance in Sails.JS?

Question

I am attempting to use the subscribe function described here. However, when editing /assets/js/app.js, I am getting this error:

Uncaught Referen         


        

Answer 1

To subscribe to a model instance, I use the following Real-Time Model Event pattern, some of which resides on the client and some on the server. Keep in mind the client can’t just subscribe itself- you have to send a request to the server letting it know that you’d like to be subscribed-- this is the only way to do it securely. (e.g. you might want to publish notifications with sensitive information-- you want to make sure a connected socket has permission to see that information before subscribing them to it.)

I’m going to use an example of an app with a User model. Let’s say I want to notify folks when existing users login.

Client-Side (Part I)

On the client-side, for simplicity, I’m going to use the existing app.js file in the /assets/js folder (or /assets/linker/js folder if you used the --linker switch when you built the app.)

To send my socket request to the server within assets/js/app.js, I’m going to use the socket.get() method. This method mimics the functionality of an AJAX “get” request (i.e. $.get() ) but uses sockets instead of HTTP. (FYI: You also have access to socket.post(), socket.put(), and socket.delete()).

The code would look something like this:

 
// Client-side (assets/js/app.js)
// This will run the `welcome()` action in `UserController.js` on the server-side.

//...

socket.on('connect', function socketConnected() {

  console.log("This is from the connect: ", this.socket.sessionid);

  socket.get(‘/user/welcome’, function gotResponse () {
    // we don’t really care about the response
  });

//...

Server-Side (Part I)

Over in the welcome() action in UserController.js, now we can actually subscribe this client (socket) to notifications using the User.subcribe() method.

 
// api/UserController.js

//...
  welcome: function (req, res) {
    // Get all of the users
    User.find().exec(function (err, users) {
      // Subscribe the requesting socket (e.g. req.socket) to all users (e.g. users)
      User.subscribe(req.socket, users);
    });
  }

//...

Back on the client-side (Part II)...

I want the socket to ‘listen’ for messages I’m going to send it from the server. To do this I’ll use:

 
// Client-side (assets/js/app.js)
// This will run the `welcome()` action in `UserController.js` on the backend.

//...

socket.on('connect', function socketConnected() {

  console.log("This is from the connect: ", this.socket.sessionid);

  socket.on('message', function notificationReceivedFromServer ( message ) {
    // e.g. message ===
    // {
    //   data: { name: ‘Roger Rabbit’},
    //   id: 13,
    //   verb: ‘update’
    // }
  });

  socket.get(‘/user/welcome’, function gotResponse () {
    // we don’t really care about the response
  });

// ...

Back on the server-side (Part II)...

Finally, I’ll start sending out messages, server-side, by using: User.publishUpdate(id);

 
// api/SessionController.js

//...
  // User session is created
  create: function(req, res, next) {

    User.findOneByEmail(req.param('email'), function foundUser(err, user) {
      if (err) return next(err);

      // Authenticate the user using the existing encrypted password...
      // If authenticated log the user in...

      // Inform subscribed sockets that this user logged in
      User.publishUpdate(user.id, {
        loggedIn: true,
        id: user.id,
        name: user.name,
        action: ' has logged in.'
      });
    });
  }
//...

You can also check out Building a Sails Application: Ep21 - Integrating socket.io and sails with custom controller actions using Real Time Model Events for more information.