django：针对get_context_data中的get_queryset结果进行计算

Question

While using django's generic ListView, I want to include some extra context data which is calculated against the result of get_queryset, for example:

class BookListView(ListView):

    model = Book
    context_object_name = 'book_list'
    template_name = 'book_list.html'

    def get_queryset(self, *args, **kwargs):
        qset = super(BookListView, self).get_queryset(*args, **kwargs)
        return qset.filter(owner=self.request.user)

    def get_context_data(self, **kwargs):
        context = super(BookListView, self).get_context_data(**kwargs)
        // just take this as an example, here the extra context data may be some 
        // complex result which is calculated against the result of get_queryset
        context['2012_books_nr'] = self.get_queryset().filter(publish_year='2012').count()
        return context

will this cause any (performance or other) issue if I do it like above? it seems a little weird, is there any better approach for doing this?

beside of that, I'm calling the get_queryset without any args and kwargs in get_context_data, how can I ensure I'm getting the exactly the same result with what it called automatically?

It would be perfect if there is something storing the result of get_queryset before entering get_context_data, so I can just retrieve the result, does it exist?

Answer 1

除了您应该使用queryset .count()方法而不是对其调用len()之外，这还不错。