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,:dependent => :destroy
module AutoBuildItemSource
def item_source
super || build_item_source
end
end
include AutoBuildItemSource
end
解决方法
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
但是总有accept_nested_attributes_for作为替代,在设置profile_attributes时调用build.将它与委托(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).
(注意：我设置：inverse_of使Profile.validates_presence_of：用户工作并通常保存查询.)