nil:NilClass 的未定义方法“model_name”

Question

有一个消息控制器：

class MessagesController < ApplicationController
  before_filter :load_chat

  def index
    @messages = @chat.messages
  end

  def create
    @message = @chat.messages.build(params[:message])
    if @message.save
      redirect_to @chat, notice: "Message sent"
    else
      render :new
    end
  end

  private

    def load_chat
      @chat = Chat.find(params[:chat_id])
    end

end

这是我的视图文件：

%h1 = @chat.name

= content_tag :div, id: 'messages', data: {url: chat_messages_path(@chat)} do
  = render @chat.messages


%h2 New message

= render 'messages/form'

这是我的消息/表单：

= simple_form_for @message do |f|
  = f.input :text
  = f.submit 'Send message', class: 'btn btn-success' 

最后是我的 routes.rb 文件：

resources :chats, only: [:index, :show, :new, :create] do
      resources :messages
end

所以问题是当我打开聊天/显示链接时收到一个错误undefined method model_name for nil:NilClass，因为正在呈现一种新消息的形式。我试图用不能完成工作的Message.new 替换@message，仍然是同样的问题。我还尝试在resources :chats 之外删除resources :messages，这起到了作用，但这是不正确的，因为聊天中有很多消息并且消息属于聊天。你知道这个表格应该如何为我工作吗？

编辑：聊天控制器：

class ChatsController < ApplicationController
  before_action :find_chat, :authenticate_user!


  def index
    @chats = current_user.chats
  end

  def show
    @chat = current_user.chats.find(params[:id])
  end

  def new
    @chat = current_user.chats.new
  end

  def create
    @chat = current_user.chats.new chat_params
    if @chat.save
      flash[:notice] = 'chat asked'
      redirect_to chats_path
    else
      render 'new'
    end
  end

  def edit
  end

  def destroy
    @chat.destroy!
    flash[:notice] = 'chat deleted'
    redirect_to chats_path
  end

  def update
    if @chat.update_attributes chat_params
      flash[:notice] = 'chat saved'
      redirect_to chat_path
    else
      redirect_to edit_chat_path(@chat)
    end
  end

  private
    def chat_params
      params.require(:chat).permit :name, :user_id
    end

    def find_chat
      @chat = current_user.chats.find(params[:id]) if params[:id]
    end
end

还有我的错误日志：

ActionView::Template::Error (undefined method `model_name' for nil:NilClass):
    1: = simple_form_for @message do |f|
    2:   = f.input :text
    3:   = f.submit 'Send message', class: 'btn btn-success' 
    4:      app/views/messages/_form.html.haml:1:in `_app_views_messages__form_html_haml___2629708334715527453_82911540'   app/views/chats/show.html.haml:9:in `_app_views_chats_show_html_haml__2381438814653998256_88403540'


  Rendered /home/titas/.rvm/gems/ruby-2.2.1/gems/actionpack-4.2.4/lib/action_dispatch/middleware/templates/rescues/_source.erb (10.9ms)   Rendered /home/titas/.rvm/gems/ruby-2.2.1/gems/actionpack-4.2.4/lib/action_dispatch/middleware/templates/rescues/_trace.html.erb (3.9ms)   Rendered /home/titas/.rvm/gems/ruby-2.2.1/gems/actionpack-4.2.4/lib/action_dispatch/middleware/templates/rescues/_request_and_response.html.erb (3.2ms)   Rendered /home/titas/.rvm/gems/ruby-2.2.1/gems/actionpack-4.2.4/lib/action_dispatch/middleware/templates/rescues/template_error.html.erb within rescues/layout (35.7ms)   Rendered /home/titas/.rvm/gems/ruby-2.2.1/gems/web-console-2.2.1/lib/web_console/templates/_markup.html.erb (0.6ms)   Rendered /home/titas/.rvm/gems/ruby-2.2.1/gems/web-console-2.2.1/lib/web_console/templates/_inner_console_markup.html.erb within layouts/inlined_string (0.5ms)   Rendered /home/titas/.rvm/gems/ruby-2.2.1/gems/web-console-2.2.1/lib/web_console/templates/_prompt_box_markup.html.erb within layouts/inlined_string (0.5ms)   Rendered /home/titas/.rvm/gems/ruby-2.2.1/gems/web-console-2.2.1/lib/web_console/templates/style.css.erb within layouts/inlined_string (0.9ms)   Rendered /home/titas/.rvm/gems/ruby-2.2.1/gems/web-console-2.2.1/lib/web_console/templates/console.js.erb within layouts/javascript (23.0ms)   Rendered /home/titas/.rvm/gems/ruby-2.2.1/gems/web-console-2.2.1/lib/web_console/templates/main.js.erb within layouts/javascript (0.5ms)   Rendered /home/titas/.rvm/gems/ruby-2.2.1/gems/web-console-2.2.1/lib/web_console/templates/error_page.js.erb within layouts/javascript (0.5ms)   Rendered /home/titas/.rvm/gems/ruby-2.2.1/gems/web-console-2.2.1/lib/web_console/templates/index.html.erb (42.8ms)

Answer 1

看不到您在哪里声明 @message？

--

错误似乎来自：

= render 'messages/form'

... 其中有：

= simple_form_for @message do |f|

--

除了在部分中使用@instance_variables 是不好的做法外，在这种情况下，您需要明确声明@message 以使其被识别。

我实际上认为您可以通过将嵌套资源传递给您的 messages/form 部分来解决问题：

#app/views/messages/_form.html.erb
= simple_form_for [@chat, @chat.messages.new] do |f| 

（顺便说一句，所有nilClass 错误基本上意味着您引用了一个尚未声明的变量）