title: Django queryset SUM positive and negative values
body: <p>I have a model which have <strong>IntegerField</strong> named as threshold.
  I need to get total <strong>SUM</strong> of threshold value regardless of negative values.</p>
  
  <pre><code>vote_threshold
  
  100
  
  -200
  
  -5
  
  result = 305
  </code></pre>
  
  <p>Right now I am doing it like this.</p>
  
  <pre><code>earning = 0
  result = Vote.objects.all().values('vote_threshold')
              for v in result:
                  if v.vote_threshold &gt;  0:
                      earning += v.vote_threshold
                  else:
                      earning -= v.vote_threshold
  </code></pre>
  
  <p>What is a faster and more proper way?</p>