Ruby on rails Rails 5.1 ActiveAdmin错误未定义方法“klass'；零级：零级

当我试图通过ActiveAdmin的仪表板查看两个特定模型时，我收到以下错误。我读到的所有内容都指向一个可能的关联问题，但我不确定如何纠正它。我看到很多人都有同样的问题，但还没有找到解决办法。任何帮助都将不胜感激

NoMethodError in Admin::Listings#index
undefined method `klass' for nil:NilClass

或

模型

class Company < ApplicationRecord
  has_many :appointments, through: :listings, dependent: :destroy
  has_many :listings, through: :users, dependent: :destroy
  has_many :buildings, through: :users, dependent: :destroy
  has_many :users, dependent: :destroy
end

class User < ApplicationRecord
  belongs_to :company
  has_many :apointments, through: :listings
  has_many :listings, through: :buildings
  has_many :buildings
end

class Listing < ApplicationRecord
  has_many :companies, through: :users
  has_many :users, through: :buildings
  belongs_to :building
  has_many :appointments
end

class Building < ApplicationRecord
  has_many :companies, through: :users
  belongs_to :user
  has_many :appointments, through: :listings
  has_many :listings, dependent: :destroy
end


class Appointment < ApplicationRecord
  belongs_to :listing
  has_many :companies, through: :listings 
end

class公司

我想你在

的has\u many中有一个输入错误：apointments，through:：lisings

尝试使用

has\u many:appointment，through：：listings

你缺少了一个p和一个t

没有解决方案，但看起来你的问题也一样

还有一个想法：

在具有

属于

且您使用该关联表示“通过”的模型上，尝试将其更改为“单数”。例如：

班级预约<申请记录
属于：列表
有很多：公司，通过：：上市#注意：这里是单数
终止

---

也许这会有帮助？

是的，我早些时候发现并纠正了这个问题，但仍然在这里给我相同的错误检查，您是否在纠正错误后重新启动了服务器？是的，我再次重新启动了服务器以确保出现相同的错误。我认识的一些人还建议我将一些关联单列，但这也不起作用：（如果在

rails c

中启动应用程序，是否可以浏览所有关联？

class Company < ApplicationRecord
  has_many :appointments, through: :listings, dependent: :destroy
  has_many :listings, through: :users, dependent: :destroy
  has_many :buildings, through: :users, dependent: :destroy
  has_many :users, dependent: :destroy
end

class User < ApplicationRecord
  belongs_to :company
  has_many :apointments, through: :listings
  has_many :listings, through: :buildings
  has_many :buildings
end

class Listing < ApplicationRecord
  has_many :companies, through: :users
  has_many :users, through: :buildings
  belongs_to :building
  has_many :appointments
end

class Building < ApplicationRecord
  has_many :companies, through: :users
  belongs_to :user
  has_many :appointments, through: :listings
  has_many :listings, dependent: :destroy
end


class Appointment < ApplicationRecord
  belongs_to :listing
  has_many :companies, through: :listings 
end