Creating new observable methods for an ActiveRecord model (See related posts)

class ProjectObserver < ActiveRecord::Observer
  def new_update(callback_method, object, developer = nil)
    if developer
      send(callback_method, object, developer) if respond_to?(callback_method)
    else 
      old_update(callback_method, object)
    end
  end
  alias_method :old_update, :update
  alias_method :update, :new_update

  def before_add_developer(project, developer)
    puts "Adding #{developer}..."
  end
  
  def after_add_developer(project, developer)
    puts "Added #{developer}..."
  end
  
  def after_save(project)
    puts "Project saved..."
  end
end

class Project < ActiveRecord::Base
  has_and_belongs_to_many :developers

  def add_developer(developer)
    self.class.changed
    self.class.notify_observers(:before_add_developer, self, developer)
    transaction do
      self.developers << developer
      self.save
    end
    self.class.changed
    self.class.notify_observers(:after_add_developer, self, developer)
  end
end