Concern version of https://gist.github.com/uberllama/7505406

gistfile1.rb

# app/models/user.rb
class User < ActiveRecord::Base
  include UserObserver
  has_many :galleries
end

# /app/models/concerns/user_observer.rb
module UserObserver
  extend ActiveSupport::Concern
  
  included do
    after_create :create_default_gallery, :send_welcome_email
  end
  
  private
  
  def create_default_gallery
    galleries.create(name: "Default gallery")
  end
  
  def send_welcome_email
    UserMailer.delay.welcome(id)
  end
  
end