ruby-on-rails - 如何在关闭 cache_classes 的情况下使用来自中间件的域对象？

Question

在rails开发环境中，cache_classes是关闭的，所以你可以修改app/下的代码，不用重启服务器就可以看到变化。

不过，在所有环境中，中间件只会创建一次。所以如果我有这样的中间件:

class MyMiddleware

  def initialize(app)
    @app = app
  end

  def call(env)
    env['model'] = MyModel.first
  end

end

我在 config/environments/development.rb 中执行此操作:

config.cache_classes = false # the default for development
config.middleware.use MyMiddleware

那么我总是会得到以下错误:

A copy of MyMiddleware has been removed from the module tree but is still active!
  /Library/Ruby/Gems/1.8/gems/activesupport-2.3.2/lib/active_support/dependencies.rb:414:in `load_missing_constant'
  /Library/Ruby/Gems/1.8/gems/activesupport-2.3.2/lib/active_support/dependencies.rb:96:in `const_missing'
  /Users/me/projects/my_project/lib/my_middleware.rb:8:in `call'
  /Library/Ruby/Gems/1.8/gems/actionpack-2.3.2/lib/action_controller/middleware_stack.rb:72:in `new'
  ...

问题是 MyMiddleware 实例在系统加载时创建一次，但 MyModel 类在每次调用时都会重新加载。

我试过 'MyModel'.constantize.first 延迟绑定(bind)到类，直到方法调用时间，但这将问题变成了一个新问题:

You have a nil object when you didn't expect it!
The error occurred while evaluating nil.include?
  /Library/Ruby/Gems/1.8/gems/activerecord-2.3.2/active_record/attribute_methods.rb:142in `create_time_zone_conversion_attribute?'
  /Library/Ruby/Gems/1.8/gems/activerecord-2.3.2/active_record/attribute_methods.rb:75:in `define_attributes_methods'
  ...

Answer 1

这似乎是一个 Rails 错误。查看您是否可以将 Rails 版本升级到 2.3.4 或 2.3.5。

我相信this是解决问题的提交。原始错误报告是 here .