rails g migration AddManagerToUsers manager:references

​

class AddManagerToUsers < ActiveRecord::Migration[6.0]

  def change

    add_reference :users, :manager, foreign_key: { to_table: :users }

  end

end

​

class User < ActiveRecord::Base

  belongs_to :manager, class_name: 'User', optional: true

  has_many :employees, class_name: 'User', foreign_key: 'manager_id'

end