多態關聯並設置資產的默認值

Question

新手問題。我有以下型號：

class Asset < ActiveRecord::Base 
    belongs_to :assetable, :polymorphic => true 
    #paperclip 
    has_attached_file :asset, 
    :hash_secret => "my-secret", 
    :url => "/images/:hash_:basename_:style.:extension", 
    :path => UPLOAD_PATH + "/:hash_:basename_:style.:extension", 
    :styles => { :medium => "300x300>", :thumb => "75x75>" 

    } 
end 

class Location < ActiveRecord::Base 
    has_many :assets, :as => :assetable, :dependent => :destroy 
end 

class MenuItem < ActiveRecord::Base 
    has_many :assets, :as => :assetable 
end 

我的資產有一個名爲description的屬性。如果assetable_type是一個「MenuItem」並且描述爲零，我希望描述是關聯的menu_item的正文。我將如何做到這一點？

THX

Answer 1

class Asset < ActiveRecord::Base 
    before_save :set_description 

    private 

    def set_description 
     self.description ||= assetable.body if assetable.is_a?(MenuItem) 
    end 
end 

---

或修改訪問

def description 
    return self[:description] unless self[:description].blank? 
    assetable.description if assetable.is_a? MenuItem 
end