generic_relation.py

class Customer(models.Model):
    content_type = models.ForeignKey(ContentType, on_delete=models.CASCADE)
    object_id = models.IntegerField()
    content_object = GenericForeignKey()


class Individual(models.Model):
    user = models.ForeignKey(User, on_delete=models.CASCADE)
    name = models.CharField('Nome', max_length=200)
    brazilian_cpf = models.CharField('CPF', max_length=14, unique=True, blank=True, null=True)
    customer = GenericRelation(Customer)

    class Meta:
        verbose_name = 'Pessoa Física'
        verbose_name_plural = 'Pessoas Físicas'

    def __str__(self):
        return self.name


class LegalPerson(models.Model):
    user = models.ForeignKey(User, on_delete=models.CASCADE)
    name = models.CharField('Nome', max_length=200)
    registered_number = models.CharField('CNPJ', max_length=18, unique=True, default='', blank=True)
    customer = GenericRelation(Customer)

    class Meta:
        verbose_name = 'Pessoa Jurídica'
        verbose_name_plural = 'Pessoas Jurídicas'

    def __str__(self):
        return self.name


class Order(models.Model):
    cost = models.DecimalField(max_digits=19, decimal_places=2)
    customer = models.ForeignKey(Customer, on_delete=models.CASCADE)

    class Meta:
        verbose_name = 'Pedido'
        verbose_name_plural = 'Pedidos'

    def __str__(self):
        return self.customer.name