5

我有三个模型：

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，在执行过程中，如果我将一个包添加到 release_item 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')
=> #<ReleaseItem id: nil, filename: "MAESTRO.TXT", created_by: nil, title: nil, sauce_author: nil, sauce_group: nil, sauce_comment: nil, filedate: nil, filesize: nil, created_at: nil, updated_at: nil, content: nil>
>> pack = Pack.new(:filename=>'legion01.zip', :year=>1998)
=> #<Pack id: nil, filename: "legion01.zip", created_by: nil, filesize: nil, items: nil, year: 1998, month: nil, filedate: nil, created_at: nil, updated_at: nil>
>> item.pack = pack
=> #<Pack id: nil, filename: "legion01.zip", created_by: nil, filesize: nil, items: nil, year: 1998, month: nil, filedate: nil, created_at: nil, updated_at: nil>
>> item.pack.filename
NoMethodError: undefined method `filename' for #<Class:0x2196318>
    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
>>

看来我应该可以访问 item.pack，但它不知道该包是一个包项目。

4

3 回答 3

6

看来您对 has_one :through 的使用是正确的。您看到的问题与保存对象有关。为了使关联起作用，被引用的对象需要有一个 id 来填充model_id对象的字段。在这种情况下，需要填写PackReleaseItems一个pack_id和一个字段才能使关联正常工作。release_item_id在通过关联访问对象之前尝试保存。

于 2008-09-18T04:25:41.847 回答
2

您的问题在于您如何将 和 关联ReleaseItem起来Pack。

has_many :through并且has_one :through两者都通过一个也充当连接表的对象工作，在这种情况下PackReleaseItem。由于这不仅仅是一个连接表（如果是，您应该只使用has_manywithout :through），正确创建关联需要创建连接对象，如下所示：

>> item.pack_release_items.create :pack => pack

您对item.pack = pack调用所做的只是将内存中的对象关联起来。当你再去查找它时，它看起来是 " through" the pack_release_items，它是空的。

于 2008-09-18T04:36:38.107 回答
1

您想要保存或创建（而不是新建）项目和包装。否则，数据库没有为关联分配 id。

于 2008-09-18T04:53:59.283 回答