title: Django set range for integer model field as constraint
body: <p>I have a django model,</p>
  
  <pre><code>class MyModel(models.Model)
      qty = model.IntegerField()
  </code></pre>
  
  <p>where I want to set constraint for <code>qty</code> something like this,  >0 or &lt;0,i.e the <code>qty</code> can be negative or positive but can not be 0.</p>
  
  <p>Is there any straight forward way to do this in Django?</p>