Fixed #23774 -- Clarified QuerySet.order_by() and related models.

    Entry.objects.order_by('blog__name', 'headline')

If you try to order by a field that is a relation to another model, Django will

use the default ordering on the related model (or order by the related model's

use the default ordering on the related model, or order by the related model's

primary key if there is no :attr:`Meta.ordering

<django.db.models.Options.ordering>` specified. For example::

<django.db.models.Options.ordering>` specified. For example, since the ``Blog``

model has no default ordering specified::

    Entry.objects.order_by('blog')

    Entry.objects.order_by('blog__id')

...since the ``Blog`` model has no default ordering specified.

If ``Blog`` had ``ordering = ['name']``, then the first queryset would be

identical to::

    Entry.objects.order_by('blog__name')

.. versionadded:: 1.7