FactoryGirl + mongoid embeddedの書き方

mongoidを使っていて、embedde属性の場合のFactoryGirlの書き方

mongoidクラス

schedule.rb

class Schedule
  include Mongoid::Document
  embeds_many :milestones

  field :title
end

milestone.rb

class Milestone
  include Mongoid::Document
  field :name, type: String
  field :date, type: String
end

FactoryGirl

FactoryGirl.define do
  factory :schedule_base, class: Schedule do
    title "testtitle"
    milestones { [build(:milestone_1), build(:milestone_2)] }
  end

  factory :milestone_1, class: Milestone do
    name "mile1"
    date "20140516"
  end
  factory :milestone_2, class: Milestone do
    name "mile2"
    date "20140520"
  end
end

参考サイト