newbie: unique and ForeignKey

[Emanuele]

Toy problem: I have a list of persons and a sublist of it are
friends. Each list shouldn't have duplicates (it means
there is no more than one guy with a given pair <name,surname>,
I know it's not a good assumption in general but this is a
toy example ;). So I made two models (Person, Friend) the first
having the constraint "unique_together = (("name","surname"),)"
and the second (made of just a reference to Person) having
unique=True. This last constraint doesnt'work, giving a long
traceback in admin interface. How should I express this constraint
in the proper way? What's wrong?
Example code follows.

Thanks in advance,

Emanuele

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from django.core import meta


class Person(meta.Model):
    name = meta.CharField("Name",maxlength=30)
    surname = meta.CharField("Surname",maxlength=30)


    def __repr__(self):
        return "%s %s" % (self.name,self.surname)


    class META:


        unique_together = (("name","surname"),)


        admin = meta.Admin()
        pass


    pass




class Friend(meta.Model):
    person = meta.ForeignKey(Person,verbose_name="Friend",unique=True)


    def __repr__(self):
        return "%s" % (self.get_person())


    class META:
        admin = meta.Admin()
        pass


    pass
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