ensuring that a value is set in api request with promise

I do not think I am using promises correctly in the apiRequest function below. As you can see, the function apiRequest gets triggered by a click of a button. I assumed that the clickToTrigger function would block until the apiRequest has finished and todos has been set, however, I sometimes get error message that todos is undefined in code that runs later on in clickToTrigger function. Is it possible that I have written the promise incorrectly. How should I write the apiRequest to ensure that the code (not displayed) in clickToTrigger won't run until the todos are set?

apiRequest: function(){
                        var that = this;
                        var datasource = 'http://ift.tt/1C9qqUT';
                         return new Ember.$.ajax({url: datasource, dataType: "json", type: 'GET'}).then(function(data){  
                             that.set('todos', data);
                             }); 
                     },


 actions: {
     clickToTrigger: function(){
                         this.apiRequest();
                         todo = this.store.createRecord('index', {
                                          todos: this.get('todos'),                                                                           
                             });
                         todo.save();
                         //code moves on to do other things that need the todos but they are undefined...
                    }
    },