Rails：如何访问新记录的嵌套关联的父模型？ [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Post&评论模型，Post有 accepts_nested_attributes_for：commments 和：autosave =>

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

我们可以创建一个新帖子以及一些新的评论，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'

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

1. 此评论未附加到信息（无效）


2. 此评论附加到未保存的信息（有效）

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，只需调用 self.post from注释不工作，因为根据上面的，它返回nil直到保存发生后。在回调当然，我不（不应该）访问@post，只有自己的

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.

那么：从嵌套关联模型的角度来看，我如何访问新记录的嵌套关联的父模型？

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

（FWIW，我使用它的实际示例允许人们创建一个裸体评论，然后会自动创建一个post来包含它，如果没有一个。我已经简化了这个例子，所以它不是特定于我的代码在不相干的方式。）

(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

我认为很奇怪，Rails不让你这样做。

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

有一个在Rails bug跟踪器中有很多讨论和解决方案的机票：

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

嵌套属性验证
循环
依赖

p>

And a proposed resolution:

嵌套模型：build应该直接
分配
父级

基本上，交易是，嵌套属性代码不会在子记录中设置父关联。

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

在我链接的第二张票中提到了一些解决方法。

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

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