为什么Rails的模型关联结果不自然的ActiveRecord ::关系？ [英] Why are Rails model association results not naturally ActiveRecord::Relations?

问题描述

我用Rails 3.2.0

I'm using Rails 3.2.0

让我们说我有：

class Comment < ActiveRecord::Base
  has_many :articles
end

c1 = Comment.last

然后

c1.articles.class
# => Array

c1.articles.where('id NOT IN (999999)').class
# => ActiveRecord::Relation    

为什么是一个关联的结果的的没有的键入的ActiveRecord ::关系？

这显然是/是的在某些时候的：

c1.articles.to_orig
# undefined method `to_orig' for #<ActiveRecord::Relation:0x007fd820cc80a8>

c1.articles.class
# => Array

若干评价作用于一个ActiveRecord ::关联对象，但检查类给出了不同的类型。

Certain evaluations act upon an ActiveRecord::Relation object, but inspecting the class gives a different type.

特别是，这打破建筑懒加载查询时使用合并来Concat的多个查询。

Particularly, this breaks building lazy-loaded queries when using merge to concat multiple queries.

推荐答案

这是一个的ActiveRecord ::关联，而 Rails是故意骗你。你可以看到这个已经在方法调用，并继续通过调用的祖先，其中包括ActiveRecord的类摆看看吧：

It is an ActiveRecord::Relation, but Rails is intentionally lying to you. You can see this already in the method calls, and continue to see it by calling ancestors, which includes a slew of ActiveRecord classes:

c1.articles.ancestors.select { |c| c.to_s =~ /ActiveRecord/ }.size  #=> 35

这表明它非常的没有的的阵列。

这是因为你在取回时调用 c1.articles 是<一个href="https://github.com/rails/rails/blob/v3.2.9/activerecord/lib/active_record/associations/collection_proxy.rb"><$c$c>ActiveRecord::Associations::CollectionProxy*,其中<一个href="https://github.com/rails/rails/blob/v3.2.9/activerecord/lib/active_record/associations/collection_proxy.rb#L39">undefines 类 （以及许多其他方法）。这意味着类通过<一个被委派href="https://github.com/rails/rails/blob/v3.2.9/activerecord/lib/active_record/associations/collection_proxy.rb#L77">its 的method_missing ，该<一href="https://github.com/rails/rails/blob/v3.2.9/activerecord/lib/active_record/associations/collection_proxy.rb#L89">sends为目标 。正如我们所看到的，类目标在这里，事实上，阵列：

This happens because what you’re getting back when calling c1.articles is an ActiveRecord::Associations::CollectionProxy*, which undefines class (along with many other methods). This means that class gets delegated via its method_missing, which sends it to target. As we can see, the class of target here is, in fact, Array:

c1.articles.target.class  #=> Array

这就是 c1.articles.class 从何而来。然而，它的是的的的ActiveRecord ::关联。

That is where c1.articles.class comes from. Nevertheless, it is an ActiveRecord::Relation.

<子> * 我们可以验证它确实是一个的ActiveRecord ::协会:: CollectionProxy 通过调用Ruby的原类有问题的对象方法： Object.instance_method（：类）.bind（c1.articles）.CALL 。这是一个很好的技巧，以验证对象是不是想pretend是一个不同的类。的

_{* We can verify that it is indeed an ActiveRecord::Associations::CollectionProxy by calling Ruby’s original class method on the object in question: Object.instance_method(:class).bind(c1.articles).call. This is a nice trick to verify that the object is not trying to pretend to be of a different class.}

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