Sometimes I have a django model that I want to behave like a singleton where there has to be one, and only one row present in the table at all times. I accomplish this by overriding the model's save() and delete() methods.

class Singleton(models.Model):
    # put model fields here

    def save(self):
        self.id=1
        super(Singleton, self).save()

    def delete(self):
        pass