title: difference between values() and only()
body: <p>what's the difference between using:</p>
  
  <pre><code>Blabla.objects.values('field1', 'field2', 'field3')
  </code></pre>
  
  <p>and</p>
  
  <pre><code>Blabla.objects.only('field1', 'field2', 'field3')
  </code></pre>