如何在Ruby on Rails中实现Active Record继承? [英] How to implement Active Record inheritance in Ruby on Rails?
问题描述
如何使用活动记录实现继承?
How to implement inheritance with active records?
例如,我想要一个类Animal,Dog类和Cat类。
For example, I want a class Animal, class Dog, and class Cat.
Rails如何支持单表继承。
How would the model and the database table mapping be?
推荐答案
From the AR docs:
Active Record允许通过
继承,将类的名称存储在默认的
列中被命名为type
(可以通过覆盖
Base.inheritance_column来改变)。这意味着
的继承看起来像这样:
Active Record allows inheritance by storing the name of the class in a column that by default is named "type" (can be changed by overwriting Base.inheritance_column). This means that an inheritance looking like this:
class Company < ActiveRecord::Base; end
class Firm < Company; end
class Client < Company; end
class PriorityClient < Client; end
当您执行Firm.create(:name =>
37signals此记录将
保存在公司表中,类型为
=Firm。然后,您可以使用Company.find(:first,name
='37signals')再次获取此行,它将返回Firm对象。
When you do Firm.create(:name => "37signals"), this record will be saved in the companies table with type = "Firm". You can then fetch this row again using Company.find(:first, "name = ‘37signals’") and it will return a Firm object.
如果你的表中没有定义类型列
,单表
继承不会被触发。在
这种情况下,它将像普通的
子类一样工作,没有特殊的魔法为
区分它们或
重新加载正确的类型与find。
If you don‘t have a type column defined in your table, single-table inheritance won‘t be triggered. In that case, it‘ll work just like normal subclasses with no special magic for differentiating between them or reloading the right type with find.
一个很好的教程在这里: http://juixe.com/techknow/index.php/2006/06/03/rails-single-table-inheritance/
A pretty good tutorial is here: http://juixe.com/techknow/index.php/2006/06/03/rails-single-table-inheritance/
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