ActiveRecord-连接多张表之单表继承

ActiveRecord-连接多张表之单表继承

1. 基本概念

2. 单表继承

# model的定义

class People 

# 迁移文件的定义，即关系型数据库的体现

create_table :people, :force => true do |t|

    t.column :type, :string

    # common attributes

    t.column :name, :string

    t.column :email, :string

    # attributes for type=Customer

    t.column :balance, :decimal, :precision => 10, :scale => 2

    # attributes for type=Employee

    t.column :reports_to, :integer

    t.column :dept, :integer

    # attributes for type=Manager

    # none

end

# 添加人员

boss = Manager.create({name: 'Jobs', email: '[email protected]', dept: 1})

empl = Employee.new({name: 'David', email: '[email protected]', dept: 2})

empl.boss = boss

empl.save

user = Customer.create({name: 'Jim', email: '[email protected]', balance: 100})

2.1 ActiveRecord如何如此简单的提供了单表继承？

2.2 如果一个新加入的开发者使用People添加了人员呢？

god = Person.create({name: 'God', email: '[email protected]'})

2.3 单表继承的优点和缺点

5. 参考

• 《Web开发敏捷之道》第2版#P341-连接多张表