has_one:通过工作怎么样？

我有三个型号:

class ReleaseItem < ActiveRecord::Base
  has_many :pack_release_items
  has_one :pack, :through => :pack_release_items
end

class Pack < ActiveRecord::Base
  has_many :pack_release_items
  has_many :release_items, :through=>:pack_release_items
end

class PackReleaseItem < ActiveRecord::Base
  belongs_to :pack
  belongs_to :release_item
end

问题是,在执行期间,如果我将一个包添加到release_item,则它不知道该包是一个包.例如:

Loading development environment (Rails 2.1.0)
>> item = ReleaseItem.new(:filename=>'MAESTRO.TXT')
=> #
>> pack = Pack.new(:filename=>'legion01.zip', :year=>1998)
=> #
>> item.pack = pack
=> #
>> item.pack.filename
NoMethodError: undefined method `filename' for #
    from /usr/local/lib/ruby/gems/1.8/gems/activerecord-2.1.0/lib/active_record/base.rb:1667:in `method_missing_without_paginate'
    from /usr/local/lib/ruby/gems/1.8/gems/mislav-will_paginate-2.3.3/lib/will_paginate/finder.rb:164:in `method_missing'
    from /usr/local/lib/ruby/gems/1.8/gems/activerecord-2.1.0/lib/active_record/associations/association_collection.rb:285:in `send'
    from /usr/local/lib/ruby/gems/1.8/gems/activerecord-2.1.0/lib/active_record/associations/association_collection.rb:285:in `method_missing_without_paginate'
    from /usr/local/lib/ruby/gems/1.8/gems/activerecord-2.1.0/lib/active_record/base.rb:1852:in `with_scope'
    from /usr/local/lib/ruby/gems/1.8/gems/activerecord-2.1.0/lib/active_record/associations/association_proxy.rb:168:in `send'
    from /usr/local/lib/ruby/gems/1.8/gems/activerecord-2.1.0/lib/active_record/associations/association_proxy.rb:168:in `with_scope'
    from /usr/local/lib/ruby/gems/1.8/gems/activerecord-2.1.0/lib/active_record/associations/association_collection.rb:281:in `method_missing_without_paginate'
    from /usr/local/lib/ruby/gems/1.8/gems/mislav-will_paginate-2.3.3/lib/will_paginate/finder.rb:164:in `method_missing'
    from (irb):5
>> 

似乎我应该可以访问item.pack,但它不知道该包是一个Pack项.

看来你对has_one:through的使用是正确的.您看到的问题与保存对象有关.要使关联起作用,正在引用的对象需要具有id来填充model_id对象的字段.在这种情况下,PackReleaseItems有一个pack_id和一个release_item_id字段需要填充以使关联正常工作.在通过关联访问对象之前尝试保存.