before_removing_callbacks_model.rb

class Customer < ActiveRecord::Base
    after_create :send_welcome_email, unless: :auto_registered?
    has_one :auto_created, dependent: :destroy

    private
    def send_welcome_email
        CustomerMailer.welcome_email(self).deliver
    end
    
    def auto_registered?
        !auto_created.nil?
    end
end