未知的屬性errror時，實現軌道多表繼承

我跟着崗位http://techspry.com/ruby_and_rails/multiple-table-inheritance-in-rails-3/實現與鐵4的多表繼承。我有三種模式：用戶，申請人和導師。這裏是我的代碼：未知的屬性errror時，實現軌道多表繼承

class User < ActiveRecord::Base 
    belongs_to :student, :polymorphic => true 
end 

class Tutor < ActiveRecord::Base 
    acts_as_student 
end 

class Applicant < ActiveRecord::Base 
    acts_as_student 
end 

# in the /lib/student_module.rb 
module Student 
    def acts_as_student 
    include InstanceMethods 
    has_one :user, :as => :student, :autosave => true, :dependent => :destroy 
    alias_method_chain :user, :build 

    user_attributes = User.content_columns.map(&:name) #<-- gives access to all columns of Business 
    # define the attribute accessor method 
    def student_attr_accessor(*attribute_array) 
     attribute_array.each do |att| 
     define_method(att) do 
      user.send(att) 
     end 
     define_method("#{att}=") do |val| 
      user.send("#{att}=",val) 
     end 
     end 
    end 
    student_attr_accessor *user_attributes #<- delegating the attributes 
    end 

    module InstanceMethods 
    def user_with_build 
     user_without_build || build_user 
    end 
    end 
end

用戶表具有用戶名，電子郵件attributes.The導師表有名字，姓氏，介紹，節目，entry_year屬性。在軌控制檯，我得到了

tutor = Tutor.new => #<Tutor id: nil, first_name: nil, last_name: nil, intro: nil, created_at: nil, updated_at: nil, entry_year: nil, program: nil> 
tutor.username 
=> ActiveRecord::UnknownAttributeError: unknown attribute: student_id

，我發現，student_attr_accessor方法是錯誤。我應該如何解決它？謝謝！

來源

2013-05-06 Yujun Wu

我發現我忘記了在用戶模型中聲明外鍵列和類型列。要解決這個問題，只需執行如下遷移：

def change 
    add_column :users, :student_id,:integer 
    add_column :users, :student_type,:string 
    end

來源

2013-05-06 18:34:28

未知的屬性errror時，實現軌道多表繼承

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