title: Django form is still full after sign up
body: <p>I have an app in django 1.11. Below is the view with the form where the user can sign up for the event, after saving he gets a message about the details - on the same page, at the same url. But, after saving the form is completed and after pressing F5 the next saving is performed. How can I avoid this?</p>
  
  <p>I think something with the form_valid method is wrong.</p>
  
  <pre><code>class EventDetailView(DetailView, CreateView):
      model = models.Event
      form_class = forms.ParticipantForm
      context_object_name = 'event'
      template_name = 'events/event_detail.html'
  
      def get_success_url(self):
          return reverse('events:detail', kwargs={'slug': self.kwargs['slug'], 'pk': self.kwargs['pk']})
  
      def form_valid(self, form):
          self.object = form.save()
          context = self.get_context_data()
          context['registered_event'] = context['event']
          return self.render_to_response(context)
  </code></pre>