attr_accessor，无法访问属性 [英] attr_accessor, not able to access property

问题描述

这可能是一个非常愚蠢的问题，但我们开始

This is probably very stupid question but here we go

class Foo < ActiveRecord::Base
 attr_accessor :group_id
end

来自irb

# gets record which has group_id set to 106    
foo = Foo.find(1)
foo.group_id
=> nil

如果我去删除

attr_accessor :group_id

attr_accessor :group_id

一切正常

foo = Foo.find(1)
foo.group_id
=> 106

我的问题是为什么?不应该 attr_accessor 为属性 :group_id 创建访问器/修改器，这就是为什么所有这些都应该工作的原因.我错过了什么?

My question is why? Shouldn't attr_accessor create accessor / mutator for property :group_id and that why all should be working. What am I missing?

更新

下面是很好的答案，就像我在这里的动机的解释一样，我想使用某些属性的批量分配(从 Rails 3.2.x 开始你需要这个).为此，您需要 attr_accessible ，我发现这样的代码更清晰，当然，如果负责任地使用:)

Good answers bellow, just as explanation for my motivation here is I want to use mass assignment of certain properties (you need this since Rails 3.2.x). For that you need attr_accessible , I find that code is much cleaner that way, of course if used responsibly :)

推荐答案

看起来 group_id 已经是你的 Foo 对象的一个​​属性(通过它返回的事实表明106 当 attr_accessor 被省略时).通过添加attr_accessor，您将覆盖已有的内容并创建一个名为group_id 的方法读取器和写入器.新定义的 group_id 的返回为零，因为您没有定义任何东西.

Looks like group_id is already a property on your Foo object (shown by the fact that it returns 106 when attr_accessor is omitted). By adding attr_accessor you are overriding what's already there and creating a method reader and writer called group_id. The return of the newly defined group_id is nil since you don't define anything.

从概念上讲，你会得到这样的结果:

Conceptually, you're ending up with something like this:

class Foo < ActiveRecord::Base
  def group_id  # overriding previous definition of 'group_id'
    nil
  end
end

<小时>

如果您的目标是公开属性，那么是的，请使用 attr_accessible

If your goal is expose properties then yes, use attr_accessible

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