Checkbox Persistance Directive with Firebase

gistfile1.js

//html 
/*
    <tasted beer="{{beer.$id}}" />
*/

var TastedDirective = angular.module('TastedDirective', []);

TastedDirective
.directive( 'tasted', function($rootScope,  $q, TastedFactory) {
    return {
      	restrict: 'AE',
     	replace: true,
      	template: '<input type="checkbox"  ng-model="result" ng-change="tick()" />',
      	controller: 'TastedController',
      	scope: {
       		beer: '@beer',
       		result: '@result'
      	},
      	link: function(scope, elem, attrs) {
      		var beer = scope.beer;

  			TastedFactory.result(beer).then(function(data){
  				console.log('then',data);
  				scope.result = data;
  			});

      	}
    }
})
.controller( 'TastedController', function($rootScope, $scope, $q, $firebase){
	$scope.tick = function(){
		var firebase_url = 'https://brilliant-fire-7870.firebaseio.com/';
		var tasted = $scope.result;
		var beerID = $scope.beer;
		var currentUser = $rootScope.firebaseUser.uid;
		var dataObject = { tasted: tasted };   
	
		var endpoint = new Firebase(firebase_url + 'tasting/' + currentUser + '/' + beerID);
		endpoint.set(dataObject);

	}
});

App.factory("TastedFactory", function($rootScope, $q, $http, $firebase) {

  var factory = {};
  var helper = {};
  var firebase_url = 'https://brilliant-fire-7870.firebaseio.com/';

  factory.result = function (beerID) {
		var currentUser = $rootScope.firebaseUser.uid;
		var endpoint = new Firebase(firebase_url + 'tasting/' + currentUser + '/' + beerID);
		var deferred = $q.defer();
				
		endpoint.once('value', function(snapshot){
			var foo = snapshot.val() || false;
			if(foo.tasted){
				console.log('tasted');
				deferred.resolve(true);
			} 
			else {
				console.log('not tasted');
				deferred.resolve(false);
			}
		});
		
		return deferred.promise;
  };

  return factory;

});