title: Django - form's ChoiceField not updating immediately
body: <p>I have created a form in <code>forms.py</code> which uses select input based on objects from the database:</p>
  
  <pre><code>from controls.models import Valve
  
  class CronjobForm(forms.Form):
      query = Valve.objects.all()
      VALVE_CHOICES = [
          (valve.pk, valve.name) for valve in query
      ]
      valves = forms.ChoiceField(required=True, widget=forms.Select, choices=VALVE_CHOICES)
  </code></pre>
  
  <p>At first, everything seemed to work just fine, the HTML's <code>&lt;select&gt;</code> with <code>option</code> got rendered. </p>
  
  <p>The problem is, when I add a new <code>Valve</code> object to the database, using the Django Admin interface, it takes a while for the <code>ChoiceField</code> field to get updated - I can't see the new option on front-end immediately. I tried to reload the page, force reload, even print out the query to the terminal - the variable <code>query</code> got updated immediately, just the HTML did not. </p>
  
  <p>It eventually gets updated after a while, minute or so, maybe thanks to the system checks or by repeating the <code>runserver</code> command.</p>
  
  <p>So I'm wondering, what am I missing? Is there some way to force update the form? Does the form get cached and that's what causes the problem? </p>