Rails：模型：类的方法“范围”答案

【问题标题】：Rails: method `scoped' for Model:ClassRails：模型：类的方法“范围”
【发布时间】：2013-01-02 17:42:30
【问题描述】：

我有两个模型：

class Forum < ActiveRecord::Base
  has_many :threads
end

class Thread < ActiveRecord::Base
  belongs_to :forum, :dependent => :destroy
  has_many :posts
end

在我看来，我试试这个：

<%= @forum.name %>
<% @forum.threads.each do |thread| %>
  <%= link_to thread.name, [@forum, thread], :class => "remote" %>
<% end %>

我在第 1 行收到此错误：

undefined method `scoped' for Thread:Class

知道这里发生了什么吗？我看到其他用户描述了这个问题，但这通常是因为他们将 has_many 复数或将 belongs_to 单数化。据我所知，我的模型制作精良。请让我知道我做错了什么。

完整的堆栈跟踪：

activerecord (3.2.9) lib/active_record/associations/association.rb:123:in `target_scope'
activerecord (3.2.9) lib/active_record/associations/association.rb:87:in `scoped'
activerecord (3.2.9) lib/active_record/associations/collection_association.rb:382:in `find_target'
activerecord (3.2.9) lib/active_record/associations/collection_association.rb:335:in `load_target'
C:in `load_target'
activerecord (3.2.9) lib/active_record/associations/collection_proxy.rb:87:in `method_missing'
app/views/forums/_show.html.erb:2:in `_app_views_forums__show_html_erb___1062139204_27502608'
actionpack (3.2.9) lib/action_view/template.rb:145:in `block in render'
activesupport (3.2.9) lib/active_support/notifications.rb:125:in `instrument'
actionpack (3.2.9) lib/action_view/template.rb:143:in `render'
actionpack (3.2.9) lib/action_view/renderer/partial_renderer.rb:265:in `render_partial'
actionpack (3.2.9) lib/action_view/renderer/partial_renderer.rb:238:in `block in render'
actionpack (3.2.9) lib/action_view/renderer/abstract_renderer.rb:38:in `block in instrument'
activesupport (3.2.9) lib/active_support/notifications.rb:123:in `block in instrument'
activesupport (3.2.9) lib/active_support/notifications/instrumenter.rb:20:in `instrument'
activesupport (3.2.9) lib/active_support/notifications.rb:123:in `instrument'
actionpack (3.2.9) lib/action_view/renderer/abstract_renderer.rb:38:in `instrument'
actionpack (3.2.9) lib/action_view/renderer/partial_renderer.rb:237:in `render'
actionpack (3.2.9) lib/action_view/renderer/renderer.rb:41:in `render_partial'
actionpack (3.2.9) lib/action_view/helpers/rendering_helper.rb:27:in `render'
app/views/forums/show.html.erb:1:in `_app_views_forums_show_html_erb___608144578_36161352'
actionpack (3.2.9) lib/action_view/template.rb:145:in `block in render'
activesupport (3.2.9) lib/active_support/notifications.rb:125:in `instrument'
actionpack (3.2.9) lib/action_view/template.rb:143:in `render'
actionpack (3.2.9) lib/action_view/renderer/template_renderer.rb:47:in `block (2 levels) in render_template'
actionpack (3.2.9) lib/action_view/renderer/abstract_renderer.rb:38:in `block in instrument'
activesupport (3.2.9) lib/active_support/notifications.rb:123:in `block in instrument'
activesupport (3.2.9) lib/active_support/notifications/instrumenter.rb:20:in `instrument'
activesupport (3.2.9) lib/active_support/notifications.rb:123:in `instrument'
actionpack (3.2.9) lib/action_view/renderer/abstract_renderer.rb:38:in `instrument'
actionpack (3.2.9) lib/action_view/renderer/template_renderer.rb:46:in `block in render_template'
actionpack (3.2.9) lib/action_view/renderer/template_renderer.rb:54:in `render_with_layout'
actionpack (3.2.9) lib/action_view/renderer/template_renderer.rb:45:in `render_template'
actionpack (3.2.9) lib/action_view/renderer/template_renderer.rb:18:in `render'
actionpack (3.2.9) lib/action_view/renderer/renderer.rb:36:in `render_template'
actionpack (3.2.9) lib/action_view/renderer/renderer.rb:17:in `render'
actionpack (3.2.9) lib/abstract_controller/rendering.rb:110:in `_render_template'
actionpack (3.2.9) lib/action_controller/metal/streaming.rb:225:in `_render_template'
actionpack (3.2.9) lib/abstract_controller/rendering.rb:103:in `render_to_body'
actionpack (3.2.9) lib/action_controller/metal/renderers.rb:28:in `render_to_body'
actionpack (3.2.9) lib/action_controller/metal/compatibility.rb:50:in `render_to_body'
actionpack (3.2.9) lib/abstract_controller/rendering.rb:88:in `render'
actionpack (3.2.9) lib/action_controller/metal/rendering.rb:16:in `render'
actionpack (3.2.9) lib/action_controller/metal/instrumentation.rb:40:in `block (2 levels) in render'
activesupport (3.2.9) lib/active_support/core_ext/benchmark.rb:5:in `block in ms'
C:/RailsInstaller/Ruby1.9.3/lib/ruby/1.9.1/benchmark.rb:295:in `realtime'
activesupport (3.2.9) lib/active_support/core_ext/benchmark.rb:5:in `ms'
actionpack (3.2.9) lib/action_controller/metal/instrumentation.rb:40:in `block in render'
actionpack (3.2.9) lib/action_controller/metal/instrumentation.rb:83:in `cleanup_view_runtime'
activerecord (3.2.9) lib/active_record/railties/controller_runtime.rb:24:in `cleanup_view_runtime'
actionpack (3.2.9) lib/action_controller/metal/instrumentation.rb:39:in `render'
actionpack (3.2.9) lib/action_controller/metal/implicit_render.rb:10:in `default_render'
actionpack (3.2.9) lib/action_controller/metal/implicit_render.rb:5:in `send_action'
actionpack (3.2.9) lib/abstract_controller/base.rb:167:in `process_action'
actionpack (3.2.9) lib/action_controller/metal/rendering.rb:10:in `process_action'
actionpack (3.2.9) lib/abstract_controller/callbacks.rb:18:in `block in process_action'
activesupport (3.2.9) lib/active_support/callbacks.rb:425:in `_run__271720943__process_action__435225614__callbacks'
activesupport (3.2.9) lib/active_support/callbacks.rb:405:in `__run_callback'
activesupport (3.2.9) lib/active_support/callbacks.rb:385:in `_run_process_action_callbacks'
activesupport (3.2.9) lib/active_support/callbacks.rb:81:in `run_callbacks'
actionpack (3.2.9) lib/abstract_controller/callbacks.rb:17:in `process_action'
actionpack (3.2.9) lib/action_controller/metal/rescue.rb:29:in `process_action'
actionpack (3.2.9) lib/action_controller/metal/instrumentation.rb:30:in `block in process_action'
activesupport (3.2.9) lib/active_support/notifications.rb:123:in `block in instrument'
activesupport (3.2.9) lib/active_support/notifications/instrumenter.rb:20:in `instrument'
activesupport (3.2.9) lib/active_support/notifications.rb:123:in `instrument'
actionpack (3.2.9) lib/action_controller/metal/instrumentation.rb:29:in `process_action'
actionpack (3.2.9) lib/action_controller/metal/params_wrapper.rb:207:in `process_action'
activerecord (3.2.9) lib/active_record/railties/controller_runtime.rb:18:in `process_action'
actionpack (3.2.9) lib/abstract_controller/base.rb:121:in `process'
actionpack (3.2.9) lib/abstract_controller/rendering.rb:45:in `process'
actionpack (3.2.9) lib/action_controller/metal.rb:203:in `dispatch'
actionpack (3.2.9) lib/action_controller/metal/rack_delegation.rb:14:in `dispatch'
actionpack (3.2.9) lib/action_controller/metal.rb:246:in `block in action'
actionpack (3.2.9) lib/action_dispatch/routing/route_set.rb:73:in `call'
actionpack (3.2.9) lib/action_dispatch/routing/route_set.rb:73:in `dispatch'
actionpack (3.2.9) lib/action_dispatch/routing/route_set.rb:36:in `call'
journey (1.0.4) lib/journey/router.rb:68:in `block in call'
journey (1.0.4) lib/journey/router.rb:56:in `each'
journey (1.0.4) lib/journey/router.rb:56:in `call'
actionpack (3.2.9) lib/action_dispatch/routing/route_set.rb:601:in `call'
warden (1.2.1) lib/warden/manager.rb:35:in `block in call'
warden (1.2.1) lib/warden/manager.rb:34:in `catch'
warden (1.2.1) lib/warden/manager.rb:34:in `call'
actionpack (3.2.9) lib/action_dispatch/middleware/best_standards_support.rb:17:in `call'
rack (1.4.1) lib/rack/etag.rb:23:in `call'
rack (1.4.1) lib/rack/conditionalget.rb:25:in `call'
actionpack (3.2.9) lib/action_dispatch/middleware/head.rb:14:in `call'
actionpack (3.2.9) lib/action_dispatch/middleware/params_parser.rb:21:in `call'
actionpack (3.2.9) lib/action_dispatch/middleware/flash.rb:242:in `call'
rack (1.4.1) lib/rack/session/abstract/id.rb:205:in `context'
rack (1.4.1) lib/rack/session/abstract/id.rb:200:in `call'
actionpack (3.2.9) lib/action_dispatch/middleware/cookies.rb:341:in `call'
activerecord (3.2.9) lib/active_record/query_cache.rb:64:in `call'
activerecord (3.2.9) lib/active_record/connection_adapters/abstract/connection_pool.rb:479:in `call'
actionpack (3.2.9) lib/action_dispatch/middleware/callbacks.rb:28:in `block in call'
activesupport (3.2.9) lib/active_support/callbacks.rb:405:in `_run__598850227__call__514831618__callbacks'
activesupport (3.2.9) lib/active_support/callbacks.rb:405:in `__run_callback'
activesupport (3.2.9) lib/active_support/callbacks.rb:385:in `_run_call_callbacks'
activesupport (3.2.9) lib/active_support/callbacks.rb:81:in `run_callbacks'
actionpack (3.2.9) lib/action_dispatch/middleware/callbacks.rb:27:in `call'
actionpack (3.2.9) lib/action_dispatch/middleware/reloader.rb:65:in `call'
actionpack (3.2.9) lib/action_dispatch/middleware/remote_ip.rb:31:in `call'
actionpack (3.2.9) lib/action_dispatch/middleware/debug_exceptions.rb:16:in `call'
actionpack (3.2.9) lib/action_dispatch/middleware/show_exceptions.rb:56:in `call'
railties (3.2.9) lib/rails/rack/logger.rb:32:in `call_app'
railties (3.2.9) lib/rails/rack/logger.rb:16:in `block in call'
activesupport (3.2.9) lib/active_support/tagged_logging.rb:22:in `tagged'
railties (3.2.9) lib/rails/rack/logger.rb:16:in `call'
actionpack (3.2.9) lib/action_dispatch/middleware/request_id.rb:22:in `call'
rack (1.4.1) lib/rack/methodoverride.rb:21:in `call'
rack (1.4.1) lib/rack/runtime.rb:17:in `call'
activesupport (3.2.9) lib/active_support/cache/strategy/local_cache.rb:72:in `call'
rack (1.4.1) lib/rack/lock.rb:15:in `call'
actionpack (3.2.9) lib/action_dispatch/middleware/static.rb:62:in `call'
railties (3.2.9) lib/rails/engine.rb:479:in `call'
railties (3.2.9) lib/rails/application.rb:223:in `call'
rack (1.4.1) lib/rack/content_length.rb:14:in `call'
railties (3.2.9) lib/rails/rack/log_tailer.rb:17:in `call'
rack (1.4.1) lib/rack/handler/webrick.rb:59:in `service'
C:/RailsInstaller/Ruby1.9.3/lib/ruby/1.9.1/webrick/httpserver.rb:138:in `service'
C:/RailsInstaller/Ruby1.9.3/lib/ruby/1.9.1/webrick/httpserver.rb:94:in `run'
C:/RailsInstaller/Ruby1.9.3/lib/ruby/1.9.1/webrick/server.rb:191:in `block in start_thread'

【问题讨论】：

你能发布完整的堆栈跟踪吗？
我已经添加了堆栈跟踪。
谢谢！ _show.html.erb:2 是link_to 调用吗？
其实就是之前的那一行。真正的第 1 行是“”。为了清楚起见，我添加了完整视图。
你发的erb是show.html.erb还是_show.html.erb？错误发生在部分。

标签： ruby-on-rails activerecord

【解决方案1】：

问题是由你的模型类名称Thread引起的，因为它也是一个标准的Ruby类的名称。

当 Rails 尝试查找关联的目标类时，它使用内部类 Thread（它没有 scoped 方法）而不是您的模型类。

有两种解决方案：

1。 重命名模型（最佳解决方案）

class Topic < ActiveRecord::Base #Thread class
end

class Forum < ActiveRecord::Base
  has_many :topics
end

这样您仍然可以保留原来的关联名称：

class Forum < ActiveRecord::Base
  has_many :theads, class_name: 'Topic'
end

2。 将您的 Thread 模型放入模块中（有效，但可能会产生不必要的副作用）

class MyApp::Thread < ActiveRecord::Base
end

class Forum < ActiveRecord::Base
  has_many :threads, class_name: 'MyApp::Thread'
end

您也可以将所有您的模型和控制器放在一个模块中。 Rails 首先在当前模块中查找常量，因此您的 Thread 类将首先找到。这还有一个好处是您不必在关联或控制器操作中显式指定class_name。

class MyApp::Thread < ActiveRecord::Base
end

class MyApp::Forum < ActiveRecord::Base
  has_many :threads # Works!
end

class MyApp::ThreadsController < ApplicationController
  def show
    @thread = Thread.find(params[:id]) # Works!
  end
end

但是您还必须更改您的routes.rb 以考虑模块，并且您在视图中的输入名称都将以模块名称为前缀，因此即使此解决方案看起来很干净，它也可能不是您想要的.

【讨论】：

优秀。将 Thread 类名称更改为 ForumTopic，现在可以正常工作了。

【解决方案2】：

也许这个构造：[@forum, thread] 正在让 rails 在 config/routes.rb 中寻找嵌套资源，例如

resources :forums do
    resources :threads
end

【讨论】：