Observer example 1

gistfile1.rb

# config/application.rb
config.autoload_paths << "#{config.root}/app/models/observers"
config.active_record.observers = :user_observer

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

# app/models/observers/user_observer.rb
class UserObserver < ActiveRecord::Observer
  
  def after_create(user)
    create_default_gallery(user)
    send_welcome_email(user)
  end
  
  private
  
  def create_default_gallery(user)
    user.galleries.create(name: "Default gallery")
  end
  
  def send_welcome_email(user)
    UserMailer.delay.welcome(user.id)
  end

end