Cancan - 当用户限制在某些网站时，新表单会失败

I have users

我有用户

class User < ActiveRecord::Base
  devise :database_authenticatable,
         :recoverable, :rememberable, :trackable, :validatable


  attr_accessible :email, :password, :password_confirmation,
                  :remember_me, :site_id, :role_name

  belongs_to :site

end
class User < ActiveRecord