ember promises

//For simple applications,, Ember Data's REST adapter can handle all
//asynchronous calls to the Rails server and completely insulate the
//dev from worrying about what happens when the server takes longer
//to respond than expected.

//If ever required to make a call to the server outside of a Route object's
//Model hook, you'll need to ensure that your application responds properly
//to when the call either fails or succeeds, and not to do anything about the
//call until it returns.

//For this, Ember gives us Promises.

$.ajax("/user/4")
  done.function() { // done: perform if call succeeds
    alert("success");
  })
  fail.function() { // fail: perform if call fails
    alert("error");
  })
  always.function() {
    alert("complete"); // always: perform for all of the evers
  });

// none of these get called until the AJAX call is done.

//Promises are what lie behind the Ember Router when it makes a call in 
//the Model hook, pauses for it to resolve, then resumes operation to set up
//the controller
//Promises are what we can use if we need to make calls of our own outside the router.

//example: use promises to ensure that we wait for our Rails server to respond
// with the expanded photo, and to react appropriately whether it succeeded or failed.
//*if using Ember Data we HAVE to rely on promises"

App.ProfilePhotoView = Ember.View.extend({
  click.function(evt) {
    this.get('controller').send('expandProfilePhoto');
  }
});

App.ProfilePhotoController = Ember.ObjectController.extend){
  actions: {
    expandProfilePhoto: function() {
      this.get('store').find('profile_photo', this.get('user_id')).then(
        // fulfill
        function(answer) {
          // display expanded profile photo
        },
          // reject
        function(e) {
          // display error message
        });
    }
  }
});

// the find method in Ember Data doesn't return the object it's found.
//What it returns is a Promise. To use that promise properly,
//we can chain a 'then' method on to the end.
//essentially, Promise.then() says, 
//"Once you're done, depnding on what happens, these are the callbacks I want run."

//The first callback we provide is the fulfill method -what to do if it succeeds.
//The second is what happens if it rejects, or errors out.

//If you don't lean on Promises, you'll feel tied to only using Ember's model hook in
//the route to get data from the server.
//That can get limiting fast and will lead to some bad dead ends.