Ruby on rails开发从头来（五十八）- ActiveRecord基础（自关联）

Ruby on rails开发从头来（五十八）- ActiveRecord基础（自关联）2011-12-04 博客园 Cure或许存在这样的情况，在一个表中，一条记录关联到表中的另一条记录，例如，公司中的每个雇员都有上级和下级，而他们同时又是雇员，在Rails中你可以这样使用Employee类：

class Employee < ActiveRecord::Basebelongs_to :manager,:class_name => "Employee",:foreign_key => "manager_id"belongs_to :mentor,:class_name => "Employee",:foreign_key => "mentor_id"has_many :mentored_employees,:class_name => "Employee",:foreign_key => "mentor_id"has_many :managed_employees,:class_name => "Employee",:foreign_key => "manager_id"end

让我们使用一些数据，这里雇员Clem和Dawn都有上级和下级：

Employee.delete_alladam = Employee.create（:id => 1, :name => "Adam"）beth = Employee.create（:id => 2, :name => "Beth"）clem = Employee.new（:name => "Clem"）clem.manager = adamclem.mentor = bethclem.save！dawn = Employee.new（:name => "Dawn"）dawn.manager = adamdawn.mentor = clemdawn.save！

现在我们可以通过关联，来回答“X的下属是谁？”，“Y的上级是谁？”。

p adam.managed_employees.map {|e| e.name} # => [ "Clem", "Dawn" ]p adam.mentored_employees # => []p dawn.mentor.name # => "Clem"