class CerfaHaveUser < ActiveRecord::Migration class Cerfa < ApplicationRecord belongs_to :dossier end class Dossier < ApplicationRecord belongs_to :user end class User < ApplicationRecord end def change add_reference :cerfas, :user, references: :users Cerfa.all.each do |cerfa| cerfa.user_id = cerfa.dossier.user.id cerfa.save end end end