Published Jun 03, 2022
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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[7.0]
def change
create_table :employees do |t|
t.references :manager, foreign_key: { to_table: :employees }
t.timestamps
end
end
end