error callback in angular resource like

Question

I'm having trouble while using ng-resource in django because it always removes the trailing slash. So I follow https://stackoverflow.com/users/192810/misko-hevery guide https://stackoverflow.com/a/11850027 by creating my own resource. I wanna ask if my code is the proper way to implement error callback function? IE: my response from server like this {err : "That book already exists!"}

angular.module('myApp').factory('Book', function($http) {
  var Book = function(data) {
    angular.extend(this, data);
  }

  Book.get = function(id) {
    return $http.get('/Book/' + id).then(function(response) {
      return new Book(response.data);
    });
  };

  Book.prototype.create = function() {
    var book = this;
    return $http.post('/Book/', book).then(function(response) {
      book.id = response.data.id;
      return book;
    });
  }

  return Book;
});

Is is ok to modify the create method like this?

Book.prototype.create = function() {
    var book = this;
    return $http.post('/Book/', book).then(function(response) {
      book.id = response.data.id;
      return book;
    }, function(response){
      book.err = response.err
      return book;
    });
  }

I modify the controller like this

var AppController = function($scope, Book) {
  $scope.err = ""
  // to create a Book
  var book = new Book();
  book.name = 'AngularJS in nutshell';
  book.create().then(function(){
    //check error, if exists pass the error message to scope
    if(typeof book.err !== "undefined"){
      $scope.err = book.err
    }
  );

};