title: Django model, how to create varying choices in model field based on form submitted?
body: <p>Suppose I have a model for books, and a page that user can submit a form to filter books. After a user submit a form, display a result page that has a checkbox for each book, and then user can select some books(at least 1) from the result page and submit a new form.</p>
  
  <p>My question is since the result page depends on the first form submitted, how can I dynamically create a varying choices on the result page?</p>