title: Django Queryset absolute value of the annotated field
body: <p>How do I get the absolute value of the annotated field? I tried the code below but it did't work.</p>
  
  <pre><code>queryset.annotate(relevance=abs(F('capacity') - int( request.GET['capacity']) ) ).order_by('relevance')
  </code></pre>
  
  <p><strong>Error:</strong></p>
  
  <p><code>TypeError: bad operand type for abs(): 'CombinedExpression'</code></p>
  
  <p>Thanks in advance!</p>