ruby-on-rails – rails：devise,cancan,rolify以获取用户的角色

if user.has_role? :admin

如何获取用户的角色名称？
就像是

users = User.all
user.each{ |user|
  puts user.role or users.role_name  ?
}

用户模型

class User < ActiveRecord::Base
  rolify
  # Include default devise modules. Others available are:
  # :token_authenticatable,:confirmable,# :lockable,:timeoutable and :omniauthable
  devise :database_authenticatable,:registerable,:recoverable,:rememberable,:trackable,:validatable
  # Setup accessible (or protected) attributes for your model
  attr_accessible :email,:password,:password_confirmation,:remember_me,:username,:first_name,:last_name
  # attr_accessible :title,:body
end

榜样

class Role < ActiveRecord::Base
  has_and_belongs_to_many :users,:join_table => :users_roles
  belongs_to :resource,:polymorphic => true
  attr_accessible :name,:id
  scopify
end