扶手：我如何才能访问新记录的嵌套协会父模型？ [英] Rails: How can I access the parent model of a new record's nested associations?

问题描述

假设我们有标准的邮政和放大器; Comment模型，具有邮政 accepts_nested_attributes_for：commments 和：自动保存=＆GT;真正设置。

Suppose we have the standard Post & Comment models, with Post having accepts_nested_attributes_for :commments and :autosave => true set.

我们可以共同创造一个新的职位有一些新的意见，例如：

We can create a new post together with some new comments, e.g.:

@post = Post.new :subject => 'foo'
@post.comments.build :text => 'bar'
@post.comments.first # returns the new comment 'bar'
@post.comments.first.post # returns nil :(
@post.save # saves both post and comments simultaneously, in a transaction etc
@post.comments.first # returns the comment 'bar'
@post.comments.first.post # returns the post 'foo'

不过，我需要能够从评论中的区别（例如从before_save或验证功能）

However, I need to be able to distinguish from within Comment (e.g. from its before_save or validation functions) between

1. 这条评论不附后（这是无效的）


2. 此评论被连接到的未保存的职位（有效期）

1. this comment is not attached to a post (which is invalid)
2. this comment is attached to an unsaved post (which is valid)

不幸的是，仅仅是调用 self.post 从评论不起作用，因为按照上面，它返回零，直到保存后发生。当然，在一个回调，我不（也不应该）访问@post，只有有问题的意见的自我。

Unfortunately, merely calling self.post from Comment doesn't work, because per above, it returns nil until after save happens. In a callback of course, I don't (and shouldn't) have access to @post, only to self of the comment in question.

所以：我如何才能访问新记录的嵌套协会父模型，从嵌套关联模型的角度看

So: how can I access the parent model of a new record's nested associations, from the perspective of that nested association model?

（FWIW，我用这与实际样品让人们创建一个赤裸裸的注释，然后会自动创建一个后遏制它，如果没有一个了。我已经简化这个例子所以它不是特定于无关紧要的方面我的code）

(FWIW, the actual sample I'm using this with allows people to create a naked "comment" and will then automatically create a "post" to contain it if there isn't one already. I've simplified this example so it's not specific to my code in irrelevant ways.)

推荐答案

我觉得很奇怪，Rails没有让你这样做。这也影响到子模型的验证。

I think it is strange that Rails does not let you do this. It also affects validations in the child model.

有与很多讨论一票，并在这个Rails的bug跟踪系统没有解决：

There's a ticket with much discussion and no resolution in the Rails bug tracker about this:

<一个href=\"https://rails.lighthouseapp.com/projects/8994/tickets/1943-nested-attributes-validations-circular-dependency\"相对=nofollow>嵌套属性验证
  圆
  依赖

和建议解决办法：

<一个href=\"https://rails.lighthouseapp.com/projects/8994-ruby-on-rails/tickets/2815-nested-models-build-should-directly-assign-the-parent\"相对=nofollow>嵌套模型：构建应该直接
  分配
  家长

基本上，交易是，嵌套的属性code不设置子记录的家长会。

Basically, the deal is, the nested attributes code doesn't set the parent association in the child record.

有第二售票提到了一些变通我联系。

There's some work-arounds mentioned in the second ticket I linked to.

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