使用独立的代码扩展Ruby类 [英] Extending a Ruby class with a standalone piece of code

问题描述

我有一个Rails应用程序与几个模型具有相同的结构：

  class Item1< ActiveRecord :: Base 
 WIDTH = 100 
 HEIGHT = 100 
 has_attached_file：image，styles：{original：＃{WIDTH} x＃{HEIGHT}} 
 validates_attachment：image， ：presence => true 
 end 
 
 
 class Item2< ActiveRecord :: Base 
 WIDTH = 200 
 HEIGHT = 200 
 has_attached_file：image，styles：{original：＃{WIDTH} x＃{HEIGHT}} 
 validates_attachment：image， ：presence => true 
 end 
  

实际代码比较复杂， >

我想我可以将代码的公共部分放在一个地方，然后在所有模型中使用。

是我想到的：

  class Item1< ActiveRecord :: Base 
 WIDTH = 100 
 HEIGHT = 100 
 extend CommonItem 
 end 
 
模块CommonItem 
 has_attached_file：image，styles： original：＃{WIDTH} x＃{HEIGHT}} 
 validates_attachment：image，：presence => true 
 end 
  

显然它不工作有两个原因：

1. CommonItem 不知道我调用的类方法。

CommonItem 中查找> WIDTH 和 HEIGHT


我尝试使用 而不是 extend ， class_eval 和类继承的一些方法， / p>



看来我缺少一些明显的东西。请告诉我。

解决方案

以下是我的操作方式：

  class Model 
 def self.model_method 
 putsmodel_method
 end 
 end 
 
模块Item 
 def self.included（base）
 base.class_eval do 
p base :: WIDTH，base :: HEIGHT 
 model_method 
 end 
 end 
 end 
 
 class Item1<模型
 WIDTH = 100 
 HEIGHT = 100 
 include item 
 end 
 
 class Item2<模型
 WIDTH = 200 
 HEIGHT = 200 
包括项目
 end 
  

包含方法在包含模块时被调用。

管理创建一个类似的结构，你的问题有。该模块正在调用 Model 类中的items类继承的方法。

输出：

  100 
 100 
 model_method 
 200 
 200 
 model_method 
  

I have a Rails app with several models with the same structure:

class Item1 < ActiveRecord::Base
  WIDTH = 100
  HEIGHT = 100
  has_attached_file :image, styles: {original: "#{WIDTH}x#{HEIGHT}"}
  validates_attachment :image, :presence => true
end


class Item2 < ActiveRecord::Base
  WIDTH = 200
  HEIGHT = 200
  has_attached_file :image, styles: {original: "#{WIDTH}x#{HEIGHT}"}
  validates_attachment :image, :presence => true
end

The actual code is more complicated but that's enough for simplicity.

I think I can put the common part of the code in one place and then use it in all models.

Here is what comes to my mind:

class Item1 < ActiveRecord::Base
  WIDTH = 100
  HEIGHT = 100
  extend CommonItem
end

module CommonItem
  has_attached_file :image, styles: {original: "#{WIDTH}x#{HEIGHT}"}
  validates_attachment :image, :presence => true
end

Obviously it doesn't work for two reasons:

1. CommonItem has no idea about class methods I invoke.
2. WIDTH and HEIGHT constants are looked up in CommonItem instead of Item1.

I tried to use include instead of extend, some ways of class_eval and class inheritance, but none work.

It seems I am missing something obvious. Please tell me what.

解决方案

Here's how I would do it:

class Model
  def self.model_method
    puts "model_method"
  end
end

module Item
  def self.included(base)
    base.class_eval do
      p base::WIDTH, base::HEIGHT
      model_method
    end
  end
end

class Item1 < Model
  WIDTH = 100
  HEIGHT = 100
  include Item
end

class Item2 < Model
  WIDTH = 200
  HEIGHT = 200
  include Item
end

The included method is called on a module when it's included.

I think I've managed to create a similar structure that your problem has. The module is calling the method inherited by the items classes from Model class.

Output:

100
100
model_method
200
200
model_method

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