class GenericModel(models.Model):
    model_type = models.CharField(max_length=16)

    def __init__(self, *args, **kwargs):
        for related_object in self._meta.get_all_related_objects():
            if not issubclass(related_object.model, self.__class__):
                continue

        self.model_type = '{0}.{1}'.format(self._meta.app_label, related_object.__class__.__name__.lower())

        super(GenericModel, self).__init__(self, *args, **kwargs)

class SpecializedModel(models.Model):
    pass