對模型關聯對象執行批量操作

Question

在應用程序中，國家模型包含許多城市，並且有兩種方法可在所有城市執行操作。

class Country < ActiveRecord::Base 
    has_many :cities 

    def destroy_cities 
    self.cities.each do |city| 
     city.destroy 
    end 
    end 

    def update_cities(new_status) 
    self.cities.each do |city| 
     city.status = new_status 
    end 
    end 
end 

我不知道是否有更簡單的方法來寫這些方法，就像一個不存在的self.cities.destroy和self.cities.status = new_status

對效率的角度來看，它會執行這些SQL查詢：

DELETE FROM cities WHERE country_id=#{country_id} 
UPDATE cities SET status=#{new_status} WHERE country_id=#{country_id} 

而不是運行多個查詢：

SELECT * FROM cities WHERE country_id=#{country_id} 

DELETE FROM cities WHERE id=#{city_ids[0]} 
DELETE FROM cities WHERE id=#{city_ids[1]} 
DELETE FROM cities WHERE id=#{city_ids[2]} 
... 

Answer 1

您應該可以使用delete_all和update_all activerecord方法。

如果你只是想保持國家，但刪除所有你可以做的城市;

def destroy_cities 
    self.cities.delete_all 
end 

http://apidock.com/rails/ActiveRecord/Relation/delete_all

和更新，你可以做;

def update_cities(new_status) 
    self.cities.update_all(:status => new_status) 
end 

http://apidock.com/rails/ActiveRecord/Relation/update_all