Sorting items by drag and drop in django

In my django project I show a list of books in template. Book model has position field which I use to sort books.

I'm trying to sort this list by drag and drop list items but my next code dont work well. I use JQuery UI. It works in frontend but dont change position field`s value when user drag and drop list item. Can someone help me to improve my js and view code. I am comfused. I would be grateful for any help.

models.py:

class Book(models.Model):
    title = models.CharField(max_length=200, help_text='Заголовок', blank=False)
    position = models.IntegerField(help_text='Поле для сортировки', default=0, blank=True)

    class Meta:
        ordering = ['position', 'pk']

html:

<div id="books" class="list-group">
{% for book in books %}
  <div class="panel panel-default list-group-item ui-state-default">
    <div class="panel-body">{{ book.title }}</div>
  </div>
{% endfor %}
</div>

urls.py:

url(r'^book/(?P<pk>\d+)/sorting/$',
     BookSortingView.as_view(),
     name='book_sorting')

JS:

$("#books").sortable({
      update: function(event, ui) {
            var information = $('#books').sortable('serialize');
            $.ajax({
                  url: "???",
                  type: "post",
                  data: information
            });
      },
}).disableSelection();

views.py:

class BookSortingView(View):
    @method_decorator(csrf_exempt)
    def dispatch(self, request, *args, **kwargs):
        return super(BookSortingView, self).dispatch(request, *args, **kwargs)

    def post(self, request, pk, *args, **kwargs):
        for index, pk in enumerate(request.POST.getlist('book[]')):
            book = get_object_or_404(Book, pk=pk)
            book.position = index
            book.save()
        return HttpResponse()