Ruby on rails 正在缓存具有\u多个路径的ActiveRecord对象：

当我试图缓存一个具有has_many-through:关系的ActiveRecord对象时，在重新加载或保存它之前，我无法缓存该对象

person.rb：

class Person < ActiveRecord::Base
  attr_accessible :name

  has_many :person_locations
  has_many :locations, through: :person_locations

  has_many :person_items
  has_many :items, through: :person_items
end

知道为什么缓存这个ActiveRecord对象会失败吗

轨道：3.2.14

达利：2.7

Ruby:1.9.3-p392

编辑

---

另请参见：

原来这是静噪的问题

class PersonItem < ActiveRecord::Base
  attr_accessible :item_id, :person_id

  belongs_to :item
  belongs_to :person
end

class Item < ActiveRecord::Base
  attr_accessible :description

  has_many :person_items
  has_many :people, through: :person_items
end

p = Person.create
p.items << Item.create
Rails.cache.write Time.now, p
=> false

#now if I save or reload p
p.save # or p.reload
Rails.cache.write Time.now, p
=> truthy

p = Person.new
p.items << Item.new
Rails.cache.write Time.now, p