如何在 gems 中重新开课答案

【问题标题】：how to reopen a class in gems如何在 gems 中重新开课
【发布时间】：2013-07-10 14:07:18
【问题描述】：

我在主应用程序中有相同的类和一个 gem（可安装的引擎）。
我想在 gem 中重新打开类（在主应用程序中定义）。

主应用有
app/models/test.rb

类测试
  def original_method
  结尾
结尾

在 Gemfile

宝石'gem_name'

在宝石中
app/models/test.rb

类测试 def add_method 结尾结尾

但是主应用程序引发了一个错误，即未定义 Test#original_method。
看起来测试类在 gem 中被覆盖了。为什么不重新打开？
我该如何解决这个问题？？

编辑

NoMethodError (undefined method `original_method' for #<Test:0x0000001997ca70>):
  vendor/bundle/ruby/1.9.1/gems/activemodel-3.2.13/lib/active_model/attribute_methods.rb:407:in `method_missing'
  vendor/bundle/ruby/1.9.1/gems/activerecord-3.2.13/lib/active_record/attribute_methods.rb:149:in `method_missing'
  vendor/bundle/ruby/1.9.1/bundler/gems/test_gem/app/controllers/tests_controller.rb:213:in `new'
  vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_controller/metal/implicit_render.rb:4:in `send_action'
  vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/abstract_controller/base.rb:167:in `process_action'
  vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_controller/metal/rendering.rb:10:in `process_action'
  vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/abstract_controller/callbacks.rb:18:in `block in process_action'
  vendor/bundle/ruby/1.9.1/gems/activesupport-3.2.13/lib/active_support/callbacks.rb:535:in `_run__422315203817736318__process_action__439125674649202736__callbacks'
  vendor/bundle/ruby/1.9.1/gems/activesupport-3.2.13/lib/active_support/callbacks.rb:405:in `__run_callback'
  vendor/bundle/ruby/1.9.1/gems/activesupport-3.2.13/lib/active_support/callbacks.rb:385:in `_run_process_action_callbacks'
  vendor/bundle/ruby/1.9.1/gems/activesupport-3.2.13/lib/active_support/callbacks.rb:81:in `run_callbacks'
  vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/abstract_controller/callbacks.rb:17:in `process_action'
  vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_controller/metal/rescue.rb:29:in `process_action'
  vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_controller/metal/instrumentation.rb:30:in `block in process_action'
  vendor/bundle/ruby/1.9.1/gems/activesupport-3.2.13/lib/active_support/notifications.rb:123:in `block in instrument'
  vendor/bundle/ruby/1.9.1/gems/activesupport-3.2.13/lib/active_support/notifications/instrumenter.rb:20:in `instrument'
  vendor/bundle/ruby/1.9.1/gems/activesupport-3.2.13/lib/active_support/notifications.rb:123:in `instrument'
  vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_controller/metal/instrumentation.rb:29:in `process_action'
  vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_controller/metal/params_wrapper.rb:207:in `process_action'
  vendor/bundle/ruby/1.9.1/gems/activerecord-3.2.13/lib/active_record/railties/controller_runtime.rb:18:in `process_action'
  vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/abstract_controller/base.rb:121:in `process'
  vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/abstract_controller/rendering.rb:45:in `process'
  vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_controller/metal.rb:203:in `dispatch'
  vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_controller/metal/rack_delegation.rb:14:in `dispatch'
  vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_controller/metal.rb:246:in `block in action'
  vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_dispatch/routing/route_set.rb:73:in `call'
  vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_dispatch/routing/route_set.rb:73:in `dispatch'
  vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_dispatch/routing/route_set.rb:36:in `call'
  vendor/bundle/ruby/1.9.1/gems/journey-1.0.4/lib/journey/router.rb:68:in `block in call'
  vendor/bundle/ruby/1.9.1/gems/journey-1.0.4/lib/journey/router.rb:56:in `each'
  vendor/bundle/ruby/1.9.1/gems/journey-1.0.4/lib/journey/router.rb:56:in `call'
  vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_dispatch/routing/route_set.rb:612:in `call'
  vendor/bundle/ruby/1.9.1/gems/warden-1.2.1/lib/warden/manager.rb:35:in `block in call'
  vendor/bundle/ruby/1.9.1/gems/warden-1.2.1/lib/warden/manager.rb:34:in `catch'
  vendor/bundle/ruby/1.9.1/gems/warden-1.2.1/lib/warden/manager.rb:34:in `call'
  vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_dispatch/middleware/best_standards_support.rb:17:in `call'
  vendor/bundle/ruby/1.9.1/gems/rack-1.4.5/lib/rack/etag.rb:23:in `call'
  vendor/bundle/ruby/1.9.1/gems/rack-1.4.5/lib/rack/conditionalget.rb:25:in `call'
  vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_dispatch/middleware/head.rb:14:in `call'
  vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_dispatch/middleware/params_parser.rb:21:in `call'
  vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_dispatch/middleware/flash.rb:242:in `call'
  vendor/bundle/ruby/1.9.1/gems/rack-1.4.5/lib/rack/session/abstract/id.rb:210:in `context'
  vendor/bundle/ruby/1.9.1/gems/rack-1.4.5/lib/rack/session/abstract/id.rb:205:in `call'
  vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_dispatch/middleware/cookies.rb:341:in `call'
  vendor/bundle/ruby/1.9.1/gems/activerecord-3.2.13/lib/active_record/query_cache.rb:64:in `call'
  vendor/bundle/ruby/1.9.1/gems/activerecord-3.2.13/lib/active_record/connection_adapters/abstract/connection_pool.rb:479:in `call'
  vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_dispatch/middleware/callbacks.rb:28:in `block in call'
  vendor/bundle/ruby/1.9.1/gems/activesupport-3.2.13/lib/active_support/callbacks.rb:405:in `_run__4226710667851682500__call__4227166089575601802__callbacks'
  vendor/bundle/ruby/1.9.1/gems/activesupport-3.2.13/lib/active_support/callbacks.rb:405:in `__run_callback'
  vendor/bundle/ruby/1.9.1/gems/activesupport-3.2.13/lib/active_support/callbacks.rb:385:in `_run_call_callbacks'
  vendor/bundle/ruby/1.9.1/gems/activesupport-3.2.13/lib/active_support/callbacks.rb:81:in `run_callbacks'
  vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_dispatch/middleware/callbacks.rb:27:in `call'
  vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_dispatch/middleware/reloader.rb:65:in `call'
  vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_dispatch/middleware/remote_ip.rb:31:in `call'
  vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_dispatch/middleware/debug_exceptions.rb:16:in `call'
  vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_dispatch/middleware/show_exceptions.rb:56:in `call'
  vendor/bundle/ruby/1.9.1/gems/railties-3.2.13/lib/rails/rack/logger.rb:32:in `call_app'
  vendor/bundle/ruby/1.9.1/gems/railties-3.2.13/lib/rails/rack/logger.rb:16:in `block in call'
  vendor/bundle/ruby/1.9.1/gems/activesupport-3.2.13/lib/active_support/tagged_logging.rb:22:in `tagged'
  vendor/bundle/ruby/1.9.1/gems/railties-3.2.13/lib/rails/rack/logger.rb:16:in `call'
  vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_dispatch/middleware/request_id.rb:22:in `call'
  vendor/bundle/ruby/1.9.1/gems/rack-1.4.5/lib/rack/methodoverride.rb:21:in `call'
  vendor/bundle/ruby/1.9.1/gems/rack-1.4.5/lib/rack/runtime.rb:17:in `call'
  vendor/bundle/ruby/1.9.1/gems/activesupport-3.2.13/lib/active_support/cache/strategy/local_cache.rb:72:in `call'
  vendor/bundle/ruby/1.9.1/gems/rack-1.4.5/lib/rack/lock.rb:15:in `call'
  vendor/bundle/ruby/1.9.1/gems/actionpack-3.2.13/lib/action_dispatch/middleware/static.rb:63:in `call'
  vendor/bundle/ruby/1.9.1/gems/railties-3.2.13/lib/rails/engine.rb:479:in `call'
  vendor/bundle/ruby/1.9.1/gems/railties-3.2.13/lib/rails/application.rb:223:in `call'
  vendor/bundle/ruby/1.9.1/gems/rack-1.4.5/lib/rack/content_length.rb:14:in `call'
  vendor/bundle/ruby/1.9.1/gems/railties-3.2.13/lib/rails/rack/log_tailer.rb:17:in `call'
  vendor/bundle/ruby/1.9.1/gems/rack-1.4.5/lib/rack/handler/webrick.rb:59:in `service'
  /usr/local/lib/ruby/1.9.1/webrick/httpserver.rb:138:in `service'
  /usr/local/lib/ruby/1.9.1/webrick/httpserver.rb:94:in `run'
  /usr/local/lib/ruby/1.9.1/webrick/server.rb:191:in `block in start_thread'

【问题讨论】：

请附上确切的错误。
#<0x0000001e960618>

标签： ruby-on-rails ruby gem overriding

【解决方案1】：

这是一个老问题，但我只是在寻找答案时遇到它并找到了自己的答案。这是我在 Rails 应用程序中的操作方式。基本上，不是重新打开课程，而是将代码放在 module 中并将其包含在原始课程中。

# lib/extensions/gem_name/name_of_feature.rb

module Extensions
  module GemName
    module NameOfFeature
      def self.included(base)
        base.extend ClassMethods
        base.class_eval do
          # Things like association macros here
          # I.ex. belongs_to :foo
        end
      end

      def some_instance_method
        # Do something
      end

      module ClassMethods
        def some_class_method
          # Do something
        end
      end
    end
  end
end

# config/initializers/gem_name.rb

require "extensions/gem_name/name_of_feature"

GemClassToExtend.include Extensions::GemName::NameOfFeature

所以现在你可以：

GemClassToExtend.some_class_method
GemClassToExtend.new.some_instance_method

【讨论】：

【解决方案2】：

试试

Test.class_eval do
  def original_method
  end
end

【讨论】：

【解决方案3】：

您附加的关于未定义方法original_method? 而不是original_method 的声明的例外。看起来您正试图在未定义的情况下调用末尾带有 ? 的方法。

【讨论】：

我打错了。我定义了 Test#original_method 并且异常说 original_method 没有定义。
好的，那么首先你应该做 - 确保你的引擎没有被隔离。如果是 - 那么它的模型类应该使用命名空间访问。在代码方面，请确保您声明可挂载引擎的文件没有isolate_namespace 语句。
我检查了我的engine.rb 并删除了isolate_namespace 声明。然后下一个NoMethodError: undefined method `add_method' for #<TEST:0x000000094ce560>
你需要检查为什么堆栈跟踪中的类名现在是UPPER_CASED
我再次测试得到 NoMethodError: undefined method `add_method' for #<0x000000094ce560>

【解决方案4】：

您有两个 test.rb 文件，当前环境中只加载了其中一个。我建议在您的应用程序中创建一个 mixin 模块，然后将其包含在 gem 中定义的 Test 类中。

module TestExtensions
  def original_method
  end
end

Test.include(TestExtensions)

旁白：我通常不鼓励猴子以这种方式修补 gem 依赖项。考虑对Test 进行包装。

【讨论】：