title: Can we give dynamic queryset for ModelChoiceField in django forms?
body: <p>I want create a model form, which has a foreign key in the model. Like:</p>
  
  <pre><code>class TestModel(Model):
      field1=ForeignKey(RefModel)
  </code></pre>
  
  <p>I create a form like:</p>
  
  <pre><code>class TestForm(ModelForm):
      class Meta(object):
          model = TestModel
          widgets = {'field1': RadioSelect}
  </code></pre>
  
  <p>But I want to do some limitation on the field according to the url, which means it's not constant data, what should I do to change the queryset for field1 of TestForm?</p>