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

从 AR文档< a>：

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/

这篇关于如何在Ruby on Rails中实现Active Record继承？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！