title: Ruby on Rails 3 (3.1) ActiveModel Associations (tableless nested models)
body: <p>How to impliment ActiveModel associations (tableless nested models)?</p>
  
  <p>For example: </p>
  
  <pre><code>book has many chapters
  </code></pre>
  
  <p>With ActiveRecord I would create two models and assosiate them with <strong>has_many</strong> and <strong>belongs_to</strong>. But ActiveModel doesn't have such functionality. How can I implement this?</p>