Very Important Important and Different in Rails Associations

 

00000001      Self Joins

2.10 Self Joins

In designing a data model, you will sometimes find a model that should have a relation to itself. For example, you may want to store all employees in a single database model, but be able to trace relationships such as between manager and subordinates. This situation can be modeled with self-joining associations:

class Employee < ApplicationRecord   has_many :subordinates, class_name: "Employee",                           foreign_key: "manager_id"     belongs_to :manager, class_name: "Employee", optional: true end

With this setup, you can retrieve @employee.subordinates and @employee.manager.

In your migrations/schema, you will add a references column to the model itself.

class CreateEmployees < ActiveRecord::Migration[5.0]   def change     create_table :employees do |t|       t.references :manager       t.timestamps     end   end end