from django.db import models

class Entity(models.Model):

    pass

class Country(Entity):

    name = models.CharField(max_length=30)

class EUCountry(Country):

    join_date = models.DateField()

class City(models.Model):

    name = models.CharField(max_length=30)

    country = models.ForeignKey(Country, models.CASCADE)

class EUCity(models.Model):

    name = models.CharField(max_length=30)

    country = models.ForeignKey(EUCountry, models.CASCADE)

class CountryProxy(Country):

    class Meta:

        proxy = True

class CountryProxyProxy(CountryProxy):

    class Meta:

        proxy = True

class CityCountryProxy(models.Model):

    country = models.ForeignKey(CountryProxyProxy, models.CASCADE)

class Person(models.Model):

    name = models.CharField(max_length=30)

    born = models.ForeignKey(City, models.CASCADE, related_name="+")

    died = models.ForeignKey(City, models.CASCADE, related_name="+")

class PersonProfile(models.Model):

    person = models.OneToOneField(Person, models.CASCADE, related_name="profile")