为什么 alias_method 在 Rails 模型中失败

问题描述

class Country < ActiveRecord::Base

  #alias_method :name, :langEN # here fails
  #alias_method :name=, :langEN=

  #attr_accessible :name

  def name; langEN end # here works
end

在第一次调用 alias_method 失败:

In first call alias_method fails with:

NameError: undefined method `langEN' for class `Country'

我的意思是当我执行例如 Country.first 时它会失败.

I mean it fails when I do for example Country.first.

但在控制台中我可以成功调用 Country.first.langEN，并且看到第二个调用也有效.

But in console I can call Country.first.langEN successfully, and see that second call also works.

我错过了什么?

推荐答案

ActiveRecord 使用 method_missing(AFAIK 通过 ActiveModel::AttributeMethods#method_missing) 以在第一次调用时创建属性访问器和修改器方法.这意味着当您调用 langEN 方法>alias_method 和 alias_method :name, :langEN 因未定义方法"错误而失败.明确地做别名:

ActiveRecord uses method_missing (AFAIK via ActiveModel::AttributeMethods#method_missing) to create attribute accessor and mutator methods the first time they're called. That means that there is no langEN method when you call alias_method and alias_method :name, :langEN fails with your "undefined method" error. Doing the aliasing explicitly:

def name
  langEN
end

之所以有效，是因为 langEN 方法将在您第一次尝试调用时创建(通过 method_missing).

works because the langEN method will be created (by method_missing) the first time you try to call it.

Rails 提供 alias_attribute:

Rails offers alias_attribute:

alias_attribute(new_name, old_name)

允许您为属性创建别名，包括 getter、setter 和查询方法.

Allows you to make aliases for attributes, which includes getter, setter, and query methods.

你可以改用:

alias_attribute :name, :langEN

内置的method_missing 会知道使用alias_attribute 注册的别名，并会根据需要设置适当的别名.

The built-in method_missing will know about aliases registered with alias_attribute and will set up the appropriate aliases as needed.

这篇关于为什么 alias_method 在 Rails 模型中失败的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！