[Answer]-Django admin additional field on changelist page

Well, I found it out myself.

The way to do it is to override the queryset() in BookAdmin class.

Like:

def queryset(self, request):
    return Book.objects.all().select_related('author')

That is it.
Django will load the Author in the same time it loads Book. So there will be only on database hit rather than over 100 hits.