title: How to add `:include` to default_scope?
body: <p>Searching the 'net, I found that I should use <code>:include</code>, but that does not seem to change the SQL query that is generated:</p>
  
  <pre><code>def Post #model
    default_scope :order =&gt; 'created_at DESC', :include =&gt; :author
  end
  </code></pre>
  
  <p>With or without the <code>:include</code>, the SQL is the same (i.e. it is only selecting from the posts table).</p>
  
  <p>What is the way to do this?</p>