Fixed #20659 -- Fixed PublisherDetail in CBV topic documentation.

for the paginated list of books can hang off the publisher found as the single

object. In order to do this, we need to have two different querysets:

``Publisher`` queryset for use in

    :meth:`~django.views.generic.detail.SingleObjectMixin.get_object()`

    We'll set the ``model`` attribute on the view and rely on the default

    implementation of ``get_object()`` to fetch the correct ``Publisher``

    object.

``Book`` queryset for use by :class:`~django.views.generic.list.ListView`

    The default implementation of ``get_queryset()`` uses the ``model`` attribute

    to construct the queryset. This conflicts with our use of this attribute

    for ``get_object()`` so we'll override that method and have it return

    the queryset of ``Book`` objects linked to the ``Publisher`` we're looking

    at.

    Since we have access to the ``Publisher`` whose books we want to list, we

    simply override ``get_queryset()`` and use the ``Publisher``'s

    :ref:`reverse foreign key manager<backwards-related-objects>`.

``Publisher`` queryset for use in :meth:`~django.views.generic.detail.SingleObjectMixin.get_object()`

    We'll rely on the default implementation of ``get_object()`` to fetch the

    correct ``Publisher`` object.

    However, we need to explicitly pass a ``queryset`` argument because

    otherwise the default implementation of ``get_object()`` would call

    ``get_queryset()`` which we have overridden to return ``Book`` objects

    instead of ``Publisher`` ones.

.. note::

    from books.models import Publisher

    class PublisherDetail(SingleObjectMixin, ListView):

        model = Publisher  # for SingleObjectMixin.get_object

        paginate_by = 2

        template_name = "books/publisher_detail.html"

        def get(self, request, *args, **kwargs):

            self.object = self.get_object()

            self.object = self.get_object(queryset=Publisher.objects.all())

            return super(PublisherDetail, self).get(request, *args, **kwargs)

        def get_context_data(self, **kwargs):