Django: how to prevent parent object to be deleted when deleting its child object

Class A(models.Model):
    name = models.CharField()

Class B(A):
    extra_info = models.CharField()

When I delete an B object, its parent obje开发者_如何学Pythonct A also gets deleted, how to solve this headache, thanks very much. I'm using Django 1.2.3

---

This isn't possible really in Django 1.2, but it is in Django 1.3, using on_delete.