Duplicate query in archive and year class based views

[Aymeric Augustin]

In BaseArchiveIndexView and BaseYearArchiveView, get_dated_items:

• calls get_dated_queryset, which is going trigger the evaluation of said queryset (unless pagination is enabled);
• adds a new ordering clause on the queryset before making it the object_list.

Because of the added ordering clause, the queryset will be re-evaluated when accessing context['object_list'] / context[context_object_name].

The ordering clause should probably be moved into get_dated_queryset. There are two ways to achieve this:

• Add an optional ordering parameter to get_dated_queryset. This is the fastest solution and it'll be totally backwards compatible.
• Add an API to control the order of the queryset for all views. Currently no order is enforced, unless the model's meta.ordering is set -- which is often a bad practice as it adds the sorting overhead to every query involving the models.

I'm probably going to adopt the first solution to fix this problem. The second is a larger feature request.

[Aymeric Augustin <aymeric.augustin@…>]

In [03f86a5adb930eac55dea1e903fb958c002d5bc4]:

Fixed #18354 -- Performance issue in CBV.

Prevented repeating a query twice when the model isn't ordered by
-date_field (in Meta), allow_empty is False and pagination isn't
enabled.