title: In Django, how to populate a generic relation from a single form field?
body: <p>In our application, we have model <code>A</code> that has fields for a generic relation, because it could be related to an instance of either one of two models (<code>B</code> or <code>C</code>).</p>
  
  <p>When populating a non-generic ForeignKey field, we can use the ModelChoiceField.
  Our problem is we cannot find a MultipleModelsChoiceField, whose choices would be populated from querysets on both <code>B</code> and <code>C</code>.</p>
  
  <p>How would one go about solving this problem by reusing as much as possible existing Django code ?</p>