如何在rails 3中自动生成相关的多态activerecord对象

Question

class ItemSource < ActiveRecord::Base
  belongs_to :product, :polymorphic => true
end

class RandomProduct < ActiveRecord::Base
  has_one :item_source, :as => :product, :autosave => true, :dependent => :destroy
end

我想做的是打电话:

a = RandomProduct.find(1)
a.item_source

如果item_source尚不存在(= nil),则自动构建(build_item_source).

以前,我用alias_chain_method做了这个,但是在Rails 3中不支持.
哦,我也试过这个无济于事:

class RandomProduct < ActiveRecord::Base
  has_one :item_source, :as => :product, :autosave => true, :dependent => :destroy

  module AutoBuildItemSource
    def item_source
      super || build_item_source
    end
  end  
  include AutoBuildItemSource
end

Answer 1

在Rails 3中,alias_method_chain(和alias_method,和alias)工作正常:

class User < ActiveRecord::Base
  has_one :profile, :inverse_of => :user

  # This works:
  # 
  #   def profile_with_build
  #     profile_without_build || build_profile
  #   end
  #   alias_method_chain :profile, :build
  #
  # But so does this:

  alias profile_without_build profile
  def profile
    profile_without_build || build_profile
  end
end

但总是accept_nested_attributes_for作为一种替代方案,在profile_attributes设置时调用构建.将它与delegate(可选)结合使用,您不必担心记录是否存在:

class User < ActiveRecord::Base
  has_one :profile, :inverse_of => :user
  delegate :website, :to => :profile, :allow_nil => true
  accepts_nested_attributes_for :profile
end

User.new.profile # => nil
User.new.website # => nil
u = User.new :profile_attributes => { :website => "http://example.com" }
u.profile # => #<Profile id: nil, user_id: nil, website: "http://example.com"...>

如果始终创建关联,则不需要委派(但无论如何都可能有用).

(注:我设置:inverse_of,使Profile.validates_presence_of :user工作和一般保存查询.)