получить имя foreignkey для поля

class Topping(models.Model):
    some = models.CharField(max_length=30)

class Pizza(models.Model):
    name = models.CharField(max_length=50)
    toppings = models.ForeignKey(Topping, on_delete=models.SET_NULL )

    def __unicode__(self):
        return u"%s (%s)" % (self.name, u", ".join([topping.name
                                                    for topping in self.toppings.all()]))

q = queryset.model.objects.all()
        fields = q.model._meta.get_fields()
        for x in fields:
            #if isinstance(x, ForeignKey):
             #   zzz = q.model._meta.get_field(x.name)
            print(x.name) # получаем toppings, как получить name?