Ruby on rails 无方法错误，nil:NillClass的未定义方法

想找到一种在日历中显示Klass.name、Programme.name、Topics.name和Timeslots.start的方法。当前仅显示“Topic”，而不是topics.name（请参见链接）和timeslot.starts\u。尝试了其他方法，但始终没有得到方法错误。感谢关于如何解决此问题的建议

这是日历的视图

app/views/timeslot/month.html.erb//u month\u views.html.erb

<div id="timeslots">
  <h2 id="month">
    <%= link_to "<", date: @date.prev_month %>
    <%= @date.strftime("%B %Y") %>
    <%= link_to ">", date: @date.next_month %>
  </h2>
  <%= calendar @date do |date| %>
    <%= date.day %>
    <% if @timeslots_by_date[date] %>
      <ul>
        <% @timeslots_by_date[date].each do |timeslot| %>
          <li><%= link_to timeslot.topics.name %>) <%= link_to timeslot.starts_at %></li>          
        <% end %>
      </ul>
    <% end %>
  <% end %>
</div>
<br/>

#skipped for brevity

        <% @timeslots_by_date[date].each do |timeslot| %>
          <li><%= link_to timeslot.starts_at %></li>
          <% timeslot.klass.each do |topic| %>
            <li><%= link_to topic.name %></li>
          <% end %>          
        <% end %>

#skipped for brevity

路线是

Rails.application.routes.draw do
  root to: 'posts#index'

  get '/register', to: 'users#new'
  get '/login', to: 'sessions#new'
  post '/login', to: 'sessions#create'
  get '/logout', to: 'sessions#destroy'

  get '/weekly_view', to: 'timeslots#week'
  get '/monthly_view', to: 'timeslots#month'

  resources :posts
  resources :users
  resources :categories

  resources :programmes do
    resources :topics    
  end

  resources :academies do
    resources :centres do
      resources :rooms
    end
  end

  resources :intakes do
    resources :klasses
  end

  resources :timeslots

end

这些模型都有很多：通过与所有第三个模型中声明的“属于”的关联

class Klass < ActiveRecord::Base

  belongs_to :intake
  has_many :user_klasses
  has_many :users, through: :user_klasses
  has_many :klass_programmes
  has_many :programmes, through: :klass_programmes
  has_many :klass_timeslots
  has_many :timeslots, through: :klass_timeslots  
  has_many :klass_centres
  has_many :centres, through: :klass_centres
  has_many :klass_rooms
  has_many :rooms, through: :klass_rooms  
  has_many :klass_topics
  has_many :topics, through: :klass_topics

end

class Programme < ActiveRecord::Base

  has_many :topics
  has_many :user_programmes
  has_many :users, through: :user_programmes
  has_many :programme_timeslots
  has_many :timeslots, through: :programme_timeslots
  has_many :programme_intakes
  has_many :intakes, through: :programme_intakes  
  has_many :klass_programmes
  has_many :klasses, through: :klass_programmes   

end

class Topic < ActiveRecord::Base
  belongs_to :programme
  has_many :user_topics
  has_many :users, through: :user_topics
  has_many :topic_intakes
  has_many :intakes, through: :topic_intakes
  has_many :topic_timeslots
  has_many :timeslots, through: :topic_timeslots
  has_many :klass_topics
  has_many :klasses, through: :klass_topics

end

class Timeslot < ActiveRecord::Base
  has_many :programme_timeslots
  has_many :programmes, through: :programme_timeslots
  has_many :room_timeslots
  has_many :rooms, through: :room_timeslots
  has_many :user_timeslots
  has_many :users, through: :user_timeslots
  has_many :topic_timeslots
  has_many :topics, through: :topic_timeslots
  has_many :centre_timeslots
  has_many :centres, through: :centre_timeslots  
  has_many :klass_timeslots
  has_many :klass, through: :klass_timeslots     

end

类Klass 日历助手模块如下所示

app/helpers/calendar\u helper.rb

module CalendarHelper
  def calendar(date = Date.today, &block)
    Calendar.new(self, date, block).table
  end

  class Calendar < Struct.new(:view, :date, :callback)
    HEADER = %w[Sunday Monday Tuesday Wednesday Thursday Friday Saturday]
    START_DAY = :sunday

    delegate :content_tag, to: :view

    def table
      content_tag :table, class: "calendar" do
        header + week_rows
      end
    end

    def header
      content_tag :tr do
        HEADER.map { |day| content_tag :th, day }.join.html_safe
      end
    end

    def week_rows
      weeks.map do |week|
        content_tag :tr do
          week.map { |day| day_cell(day) }.join.html_safe
        end
      end.join.html_safe
    end

    def day_cell(day)
      content_tag :td, view.capture(day, &callback), class: day_classes(day)
    end

    def day_classes(day)
      classes = []
      classes << "today" if day == Date.today
      classes << "notmonth" if day.month != date.month
      classes.empty? ? nil : classes.join(" ")
    end

    def weeks
      first = date.beginning_of_month.beginning_of_week(START_DAY)
      last = date.end_of_month.end_of_week(START_DAY)
      (first..last).to_a.in_groups_of(7)
    end
  end
end

模块日历助手
def日历（日期=date.today，&block）
日历。新建（自身、日期、块）。表格
结束
类日历类主题是一个集合，模型上的所有其他关系也是如此。您必须遍历它们才能显示它们

如果没有一个恰当的跟踪和更直接的问题，很难提供更多的帮助

嗯，
经过一些尝试，我认为问题在于我对Ruby缺乏基本的理解。下面是解决此问题的代码

app/views/timeslot/month.html.erb//u month\u views.html.erb

<div id="timeslots">
  <h2 id="month">
    <%= link_to "<", date: @date.prev_month %>
    <%= @date.strftime("%B %Y") %>
    <%= link_to ">", date: @date.next_month %>
  </h2>
  <%= calendar @date do |date| %>
    <%= date.day %>
    <% if @timeslots_by_date[date] %>
      <ul>
        <% @timeslots_by_date[date].each do |timeslot| %>
          <li><%= link_to timeslot.topics.name %>) <%= link_to timeslot.starts_at %></li>          
        <% end %>
      </ul>
    <% end %>
  <% end %>
</div>
<br/>

#skipped for brevity

        <% @timeslots_by_date[date].each do |timeslot| %>
          <li><%= link_to timeslot.starts_at %></li>
          <% timeslot.klass.each do |topic| %>
            <li><%= link_to topic.name %></li>
          <% end %>          
        <% end %>

#skipped for brevity

#为简洁起见跳过


#为简洁起见跳过

有了它，现在时间表将显示Klass.name。其余部分将被忽略，因为日历将变得笨拙。
在您的问题中，我没有看到带有回溯的完整错误消息。这种错误可能是由每一个点引起的，我猜不出是哪一个点。谢谢你看。是，现有代码没有错误消息。也许更准确的问题是如何更改控制器中的代码，以便能够在视图中显示所需的参数。注意，感谢您的观察。如何在不引发异常的情况下提供现有代码的堆栈跟踪？是否通过刷新日历页面显示服务器输出来完成？是的，如果在本地运行服务器，则可以使用“tail-n500 log/dev.log”从控制台中的dev日志获取最后500行，也可以将其导出到文件：“tail-n500 log/dev>out.part.log”。或者，正如您提到的，查看正在运行的服务器时，您可以滚动输出并在那里提取stracktrace。。。结束。刷新了页面，我相信，它生成了如gist所示的堆栈跟踪。设法解决了问题，感谢您的投入。虽然它没有直接解决这个问题，但它帮助我学到了很多东西。