doc/technical/archived_migrations/20170307122103_mailer_rels.rb
class MailerRels < ActiveRecord::Migration[5.0]
def change
execute "UPDATE mailers SET mailer = 'PostNotificationMailer' WHERE id = 3;"
execute "UPDATE emails SET mailer_id = (SELECT m.id FROM mailers m WHERE m.mailer = emails.mailer)
;"
end
end