Handling server errors in angular

ctrl.coffee

angular.module('app').controller 'UserCtrl', ($scope, User) ->
  $scope.save(user) ->
    $scope.errors = {}

    success = ->
      # do something
    error = ->
      angular.forEach result.data.errors, (errors, field) ->
        $scope.form[field].$setValidity('server', false)
        $scope.errors[field] = errors.join(', ') # e.g. username is already taken

    User.create(user).then(succes, error)

form.haml

%form name: 'form', novalidate: true, ng: { submit: "save(model)" }
  %input type: "text", name: "username", ng: { model: "user.username" }, name: "username", server: { error: "true" }
  .error ng: { show: "form.username.$dirty && form.username.$invalid" }
    %span ng: { show: "form.username.$error.server" }
      {{ errors.username }}
  %input type: "submit", value: "Save"

server_error_directive.coffee

angular.module('app').directive 'serverError', ->
  {
    restrict: 'A'
    require: '?ngModel'
    link: (scope, element, attrs, ctrl) ->
      element.on 'change', ->
        scope.$apply ->
          ctrl.$setValidity('server', true)
  }