NoMethodError（nil:NilClass 的未定义方法“获取”）

Question

问题在于使用 ActionCable 通过 Web 套接字广播数据。该错误似乎表明它来自 create 方法。

错误信息

 Rendered weight/_weight.html.erb (1.1ms)
 [ActionCable] Broadcasting to weight: "<div class=\"row\">\n  <div class=\"col-md-8 well\">\n    <p>12.0 kg</p>\n    <small>less than a minute</small>\n  </div>\n</div>"
Completed 500 Internal Server Error in 25ms (Views: 7.4ms | ActiveRecord: 10.6ms)



NoMethodError (undefined method `fetch' for nil:NilClass):

app/controllers/weight_controller.rb:7:in `create'
Rendering /usr/local/rvm/gems/ruby-2.3.4/gems/actionpack-5.0.4/lib/action_dispatch/middleware/templates/rescues/diagnostics.text.erb
Rendering /usr/local/rvm/gems/ruby-2.3.4/gems/actionpack-5.0.4/lib/action_dispatch/middleware/templates/rescues/_source.text.erb
Rendered /usr/local/rvm/gems/ruby-2.3.4/gems/actionpack-5.0.4/lib/action_dispatch/middleware/templates/rescues/_source.text.erb (0.8ms)
Rendering /usr/local/rvm/gems/ruby-2.3.4/gems/actionpack-5.0.4/lib/action_dispatch/middleware/templates/rescues/_trace.text.erb
Rendered /usr/local/rvm/gems/ruby-2.3.4/gems/actionpack-5.0.4/lib/action_dispatch/middleware/templates/rescues/_trace.text.erb (0.9ms)
Rendering /usr/local/rvm/gems/ruby-2.3.4/gems/actionpack-5.0.4/lib/action_dispatch/middleware/templates/rescues/_request_and_response.text.erb
Rendered /usr/local/rvm/gems/ruby-2.3.4/gems/actionpack-5.0.4/lib/action_dispatch/middleware/templates/rescues/_request_and_response.text.erb (1.1ms)
Rendered /usr/local/rvm/gems/ruby-2.3.4/gems/actionpack-5.0.4/lib/action_dispatch/middleware/templates/rescues/diagnostics.text.erb (25.0ms)

从 controller.rb

创建方法

def create
   @weight = Weight.new(weight_params)
   @weight.user_id = current_user.id
    if @weight.save
        ActionCable.server.broadcast "weight", render(partial: 'weight/weight', object: @weight)

    else
        flash[:danger] = "New Weight was not added!"
        redirect_to current_user
    end
end

private

def weight_params
    params.require(:weights).permit(:weight)
end

我无法弄清楚返回的内容是 nil。信息在广播中的权重是正确的这一事实表明它已将其正确保存到数据库中。想不出还有什么它在执行 'fetch' 方法。

非常确定网络套接字设置正确。见下文。

config/application.rb :

config.action_cable.mount_path = '/cable'

config/routes.rb :

mount ActionCable.server => '/cable'

weight_channel.rb :

def subscribed
  stream_from "weight"
end

weight.coffee :

 received: (data) -> 
    $("#messages").prepend(data)

Answer 1

由于缺少 config/cable.yml 文件而引发错误。

解决方案是使用具有应用程序所需设置的 config/cable.yml。即：

# Action Cable uses Redis by default to administer connections, channels, and sending/receiving messages over the WebSocket.
production:
  adapter: redis
  url: redis://localhost:6379/1

development:
  adapter: redis
  url: redis://localhost:6379/1

staging:
  adapter: redis
  url: redis://localhost:6379/1

test:
  adapter: async

解决方案出现在问题的评论中。

NoMethodError（nil:NilClass 的未定义方法“获取”）

NoMethodError (undefined method `fetch' for nil:NilClass)

ruby-on-rails

websocket

actioncable