models.py

class Book(models.Model开发者_如何学C):
    title = models.CharField()
    genre = models.ManyToManyField(Genre)

class Genre(models.Model):
    name = models.Charfield()

class ReadBook(models.Model):
    genre = models.ForeignKey(Genre)
    books = models.ManyToManyField(Book)

Also I have one ModelForm:

class ReadBookForm(ModelForm):
    class Meta:
        model = ReadBook

template.html

<form action="/add_report/" method="post">{% csrf_token %}
    {{ form.as_p }}
    <input type="submit" value="Submit" />
</form>

The purpose: By default to show a visitor only one field - genre. When he is with done this choice - show other fields from books model, related to selected genre.

inside form tag:

{{ form.genre }}
<div id="books"></div>
<input type="submit" value="Submit" disabled="yes" />

then in javascript (jQuery is great for this stuff):

$('#{{ form.genre.id }}').change(function(){
    $('#books').load('{% url get_genre_books %}', {genre: $(this).value()})
});

you must create a view that will return a html that should be placed in this div:

def get_genre_books(request):
    genre = get_object_or_404(pk=request.GET.get('genre', None))
    # here render a template or something that shouls be multiple selector of the books)
    resp = ", ".join(genre.book_set.values_list('title', flat=True))
    return HttpResponse(resp)

and of course add this view to the urls.py.

One of many solutions :) didnt' test it (written only here, so maybe small bugs somewhere) :)