Rails嵌套委托属性未更新

楷模

class User < ActiveRecord::Base has_one :meta, class_name: SeoMetum, as: :metumable, dependent: :destroy delegate :browser_title, :browser_title=, :meta_description, :meta_description=, to: :meta has_one :collection accepts_nested_attributes_for :collection after_save :save_meta_tags! def save_meta_tags! meta.save end end class Collection < ActiveRecord::Base has_one :meta, class_name: SeoMetum, as: :metumable, dependent: :destroy delegate :browser_title, :browser_title=, :meta_description, :meta_description=, to: :meta belongs_to :user after_save :save_meta_tags! def save_meta_tags! meta.save end end class SeoMetum < ActiveRecord::Base attr_accessible :metumable, :browser_title, :meta_description, :meta_keywords, :meta_author belongs_to :metumable, polymorphic: true end 

这是有效的：

  it 'meta_description' do user.meta_description = 'This is my description of the user for search results.' user.meta_description.should == 'This is my description of the user for search results.' end it 'meta_description' do the_collection = user.collection the_collection.meta_description = 'This is my description of the user for search results.' the_collection.meta_description.should == 'This is my description of the user for search results.' end 

这是不起作用的

  it 'meta_description' do user.collection.meta_description = 'This is my description of the user for search results.' user.collection.meta_description.should == 'This is my description of the user for search results.' end # => nil 

我的问题是为什么委托属性不会在嵌套属性中更新。 我应该从哪里开始考虑这个问题？ 谢谢。