subject_route.js

// Load the light version of all subjects on page load
App.ApplicationController = Em.Controller.extend({
  init: function() {
    return App.Subject.find();
  }
});

// Fetch all our previously loaded subjects
App.SubjectsRoute = Ember.Route.extend({
  model: function() {
    return App.Subject.all();
  }
});

App.SubjectRoute = Ember.Route.extend({
  // If we're loading the page directly to this route, do a normal find
  model: function(params) {
    return App.Subject.find(params.subject_id);
  },
  setupController: function(controller, model) {
    // Show what details we have for this subject (e.g. the title) immediately
    controller.set("model", model);

    // Load full details for the model and display them as soon as they arrive
    if (Em.isEmpty(model.get("text"))) {    
      App.Subject.find(model.get("id")).then(function(model) {
        return controller.set("model", model);
      });
    }
  }
});