Ruby on Rails NoMethodError：nil：NilClass的未定义方法“ []”

Question

我是Ruby的新手，目前正在使用“ rspotify” gem与Spotify API交互的Web应用程序上工作。

我有一个称为“流派”的控制器，可用于从索引页面引导搜索结果。 但是，它不会让我初始化index函数中的任何变量。

这就是我的控制器的样子

# genre_controller.rb
  def index
    if params[:search]
      @genres = RSpotify::Recommendations.generate(limit: 20, seed_genres: ['country'])
      # render :json => @songs
    else
      redirect_to root_path
    end
  end

这是我的索引页面的样子

<h1>Genre#index</h1>
<p>Find me in app/views/genre/index.html.erb</p>

<h1 class="page-header">Music Matching <%= params[:search] %></h1>
<ul>
 <% @music.each do |music| %>
   <li><%= music.name %> | <%= link_to "Show", genre_path(music.id) %></li>
 <% end %>
</ul>

这是我的路线

  get 'genre/index'
  get 'genre/show', to:'genre#show', as: 'genre'

  get 'site/index'
  root 'site#index'

我的类型控制器的第4行出现错误，我在此调用RSpotify方法。 我尝试在那里实例化的任何变量都将返回NoErrorMethod。

任何帮助表示赞赏，谢谢！

编辑：

这是我从控制台得到的例外

NoMethodError (undefined method `[]' for nil:NilClass):

app/controllers/genre_controller.rb:4:in `index'
Started GET "/genre/index?utf8=%E2%9C%93&search=hello" for 127.0.0.1 at 2018-02-19 16:14:59 -0800
Processing by GenreController#index as HTML
  Parameters: {"utf8"=>"✓", "search"=>"hello"}
Completed 500 Internal Server Error in 295ms

这是来自异常的完整跟踪堆栈

rspotify (1.27.0) lib/rspotify/recommendations.rb:101:in `initialize'
rspotify (1.27.0) lib/rspotify/recommendations.rb:97:in `new'
rspotify (1.27.0) lib/rspotify/recommendations.rb:97:in `generate'
app/controllers/genre_controller.rb:4:in `index'
actionpack (5.1.4) lib/action_controller/metal/basic_implicit_render.rb:4:in `send_action'
actionpack (5.1.4) lib/abstract_controller/base.rb:186:in `process_action'
actionpack (5.1.4) lib/action_controller/metal/rendering.rb:30:in `process_action'
actionpack (5.1.4) lib/abstract_controller/callbacks.rb:20:in `block in process_action'
activesupport (5.1.4) lib/active_support/callbacks.rb:131:in `run_callbacks'
actionpack (5.1.4) lib/abstract_controller/callbacks.rb:19:in `process_action'
actionpack (5.1.4) lib/action_controller/metal/rescue.rb:20:in `process_action'
actionpack (5.1.4) lib/action_controller/metal/instrumentation.rb:32:in `block in process_action'
activesupport (5.1.4) lib/active_support/notifications.rb:166:in `block in instrument'
activesupport (5.1.4) lib/active_support/notifications/instrumenter.rb:21:in `instrument'
activesupport (5.1.4) lib/active_support/notifications.rb:166:in `instrument'
actionpack (5.1.4) lib/action_controller/metal/instrumentation.rb:30:in `process_action'
actionpack (5.1.4) lib/action_controller/metal/params_wrapper.rb:252:in `process_action'
activerecord (5.1.4) lib/active_record/railties/controller_runtime.rb:22:in `process_action'
actionpack (5.1.4) lib/abstract_controller/base.rb:124:in `process'
actionview (5.1.4) lib/action_view/rendering.rb:30:in `process'
actionpack (5.1.4) lib/action_controller/metal.rb:189:in `dispatch'
actionpack (5.1.4) lib/action_controller/metal.rb:253:in `dispatch'
actionpack (5.1.4) lib/action_dispatch/routing/route_set.rb:49:in `dispatch'
actionpack (5.1.4) lib/action_dispatch/routing/route_set.rb:31:in `serve'
actionpack (5.1.4) lib/action_dispatch/journey/router.rb:50:in `block in serve'
actionpack (5.1.4) lib/action_dispatch/journey/router.rb:33:in `each'
actionpack (5.1.4) lib/action_dispatch/journey/router.rb:33:in `serve'
actionpack (5.1.4) lib/action_dispatch/routing/route_set.rb:834:in `call'
rack (2.0.4) lib/rack/etag.rb:25:in `call'
rack (2.0.4) lib/rack/conditional_get.rb:25:in `call'
rack (2.0.4) lib/rack/head.rb:12:in `call'
rack (2.0.4) lib/rack/session/abstract/id.rb:232:in `context'
rack (2.0.4) lib/rack/session/abstract/id.rb:226:in `call'
actionpack (5.1.4) lib/action_dispatch/middleware/cookies.rb:613:in `call'
activerecord (5.1.4) lib/active_record/migration.rb:556:in `call'
actionpack (5.1.4) lib/action_dispatch/middleware/callbacks.rb:26:in `block in call'
activesupport (5.1.4) lib/active_support/callbacks.rb:97:in `run_callbacks'
actionpack (5.1.4) lib/action_dispatch/middleware/callbacks.rb:24:in `call'
actionpack (5.1.4) lib/action_dispatch/middleware/executor.rb:12:in `call'
actionpack (5.1.4) lib/action_dispatch/middleware/debug_exceptions.rb:59:in `call'
web-console (3.5.1) lib/web_console/middleware.rb:135:in `call_app'
web-console (3.5.1) lib/web_console/middleware.rb:28:in `block in call'
web-console (3.5.1) lib/web_console/middleware.rb:18:in `catch'
web-console (3.5.1) lib/web_console/middleware.rb:18:in `call'
actionpack (5.1.4) lib/action_dispatch/middleware/show_exceptions.rb:31:in `call'
railties (5.1.4) lib/rails/rack/logger.rb:36:in `call_app'
railties (5.1.4) lib/rails/rack/logger.rb:24:in `block in call'
activesupport (5.1.4) lib/active_support/tagged_logging.rb:69:in `block in tagged'
activesupport (5.1.4) lib/active_support/tagged_logging.rb:26:in `tagged'
activesupport (5.1.4) lib/active_support/tagged_logging.rb:69:in `tagged'
railties (5.1.4) lib/rails/rack/logger.rb:24:in `call'
sprockets-rails (3.2.1) lib/sprockets/rails/quiet_assets.rb:13:in `call'
actionpack (5.1.4) lib/action_dispatch/middleware/remote_ip.rb:79:in `call'
actionpack (5.1.4) lib/action_dispatch/middleware/request_id.rb:25:in `call'
rack (2.0.4) lib/rack/method_override.rb:22:in `call'
rack (2.0.4) lib/rack/runtime.rb:22:in `call'
activesupport (5.1.4) lib/active_support/cache/strategy/local_cache_middleware.rb:27:in `call'
actionpack (5.1.4) lib/action_dispatch/middleware/executor.rb:12:in `call'
actionpack (5.1.4) lib/action_dispatch/middleware/static.rb:125:in `call'
rack (2.0.4) lib/rack/sendfile.rb:111:in `call'
railties (5.1.4) lib/rails/engine.rb:522:in `call'
puma (3.11.2) lib/puma/configuration.rb:225:in `call'
puma (3.11.2) lib/puma/server.rb:624:in `handle_request'
puma (3.11.2) lib/puma/server.rb:438:in `process_client'
puma (3.11.2) lib/puma/server.rb:302:in `block in run'
puma (3.11.2) lib/puma/thread_pool.rb:120:in `block in spawn_thread'

Answer 1

当我尝试连接到Spotify API时，出现了与上述类似的错误。 关于rspotify的文档忽略了以下事实：在使用API​​进行任何操作之前，您需要运行authenticate方法。

即

RSpotify.authenticate("<your_client_id>", "<your_client_secret>")