“未初始化的常量"包含模块时出错

问题描述

我正在尝试引用关联扩展，但出现以下错误:

I am trying to reference an association extension but it errors with:

NameError (uninitialized constant User::ListerExtension):
  app/models/user.rb:2:in `<class:User>'

这是我的实现:

class User < ActiveRecord::Base
  include ListerExtension

  has_and_belongs_to_many :roles, :uniq => true, :extend => Lister

lib/lister.rb

module ListerExtension
  def lister
    self.map(&:to_s).join(', ')
  end
end

我使用的是 Rails v3.1.3.

I am using Rails v3.1.3.

推荐答案

Andrew Marshall 对自动加载设置有一个很好的观点(有关更多信息，请参阅他链接的问题)，而且:因为您将类命名为 ListerExtension，Rails 将查找名为 lister_extension.rb - not lister.rb 的文件.它很聪明，但没有那么聪明.

Andrew Marshall has an excellent point about the auto-load setup (see the question he links for more on that), but also: Because you named your class ListerExtension, Rails will be looking for a file named lister_extension.rb - not lister.rb. It's smart, but it's not that smart.

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