022 贪婪加载(Eager loading)

Eager Loading

One way to improve performance is to cut down . the number of SQL queries. You can do this through eager loading. Learn all about it in this episode!

 

提高性能的一个途径就是减少SQL查询的次数，可以通过贪婪加载来实现。这一节就来讲述相关内容。

 

---

这个很简单，就是当查询某一个类的对象时，加上include参数，include是一个数组，数组里包含这个模型类关联的模型类的对象。

 

譬如对于下面三个模型类：

 

Task:

has_many :comments

belongs_to :project

 

Project:

has_many :tasks

Comment:

belongs_to :user

User:

has_many :comments

 

Task.find(:all, :include => :projects)
Task.find(:all, :include => [:projects, :comments])
Task.find(:all, :include => [:projects, {:comments => :user}])