rabl如何从父母那里得到属性

Question

我有以下rabl代码：

object @user

attributes :id, :email, :created_at, :last_sign_in_at, :last_sign_in_ip, :authentication_token

child :info do
  attributes :first_name, :last_name
end

child :bundles do
  attributes :bundle_id_ecp
  child :products do
    attributes :product_id_ecp
  end
end

child :email_addresses do
  attributes :address
end

child :activities do
  attributes :data
end

用户has_many：活动和

：活动属于一个activity_type模型，如下所示：

class ActivityType < ActiveRecord::Base

  has_many :activities

  attr_accessible :name
  validates_uniqueness_of :name

end

如何从my：activities rabl中的activity_types访问：name属性？