在 Ruby 1.9 中访问类变量的正确方法是什么? [英] What is the proper way to access class variables in Ruby 1.9?

问题描述

我正在尝试设置一些类变量来存储 Rails 应用程序中的路径(但我认为这更像是一个红宝石问题)

I'm trying to set some class variables to store paths in a Rails application (but I think this more a ruby question)

基本上我的班级是这样的

Basically my class looks like this

class Image < ActiveRecord::Base

   @@path_to_folder = "app/assets"
   @@images_folder = "upimages"
   @@path_to_images = File.join(@@path_to_folder, @@images_folder)

end

但是当我尝试通过执行 Image.path_to_images 从我的控制器访问 @@path_to_images 时，我得到一个 NoMethodError

But when I try to access @@path_to_images from my controller by doing Image.path_to_images, I get a NoMethodError

当我尝试使用 Image.class_eval(@@path_to_images) 时，我在 ImagesController 中得到了 未初始化的类变量 @@path_to_images

When I try with Image.class_eval( @@path_to_images ), I get uninitialized class variable @@path_to_images in ImagesController

我四处搜索，我所看到的都说这些会起作用，所以我对此感到非常困惑

I've searched around and all I've seen says those would work, so I'm very confused about this

更重要的是，我尝试使用 ruby​​ 控制台定义简单的类

What's more, I tried defining simple classes with the ruby console like so

 class Bidule
     @@foo = "foo"
     Bar = "bar"
 end

所以我尝试了所有可能的方法(包括前 2 种)来访问它们，但没有办法总是引发异常

And so I tried, I think, all the ways possible (previous 2 included) to access them but no way I always get an exception raised

推荐答案

Rails 为此功能提供了类级别的属性访问器

Rails provides class level attribute accessor for this functionality

试试

class Image < ActiveRecord::Base
  cattr_accessor :path_to_folder
  @@path_to_folder = "app/assets"
end

然后访问 path_to_folder 类变量只需使用

Then to access path_to_folder class variable just use

Image.path_to_folder

但是人们总是建议避免类变量，因为它在继承中的行为.所以你可以使用像

But people always suggest to avoid class variables due to its behavior in inheritance.So you can use constants like

class Image < ActiveRecord::Base
   PATH_TO_FOLDER = "app/assets"
end

然后你可以像这样访问常量

Then you can access the constant like

Image::PATH_TO_FOLDER

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