As far as I'm aware, there's no way to specify database-side ordering in this way as it would be too backend-specific. You may wish to resort to good old-fashioned Python sorting:
class Foo(models.Model):
name = models.CharField(max_length=128)
Foo.objects.create(name='a10')
Foo.objects.create(name='a1')
Foo.objects.create(name='a2')
ordered = sorted(Foo.objects.all(), key=lambda n: (n[0], int(n[1:])))
print ordered # yields a1, a2, 10
If you find yourself needing this kind of sorting a lot, I'd recommend making a custom models.Manager
subclass for your model that performs the ordering. Something like:
class FooManager(models.Manager):
def in_a_number_order(self *args, **kwargs):
qs = self.get_query_set().filter(*args, **kwargs)
return sorted(qs, key=lambda n: (n[0], int(n[1:])))
class Foo(models.Model):
... as before ...
objects = FooManager()
print Foo.objects.in_a_number_order()
print Foo.objects.in_a_number_order(id__in=[5, 4, 3]) # or any filtering expression