django-smart-selects | chained and grouped selects for django forms

from smart_selects.db_fields import ChainedForeignKey
...
class Person(models.Model):
    name = models.CharField(max_length=20)
    company = models.ForeignKey(Company, on_delete = models.CASCADE) 
    car = ChainedForeignKey(
        Car

class Choice(models.Model):
    choice = models.CharField(max_length=300)

    def __str__(self):
        return self.choice

class User(models.Model):
    username=models.CharField(max_length=300)

class SlotChoice(models.Model):
    slot

from smart_selects.db_fields import ChainedForeignKey

class Country(models.Model):
    .......

class City(models.Model):
    country = models.ForeignKey(Country)
    .......

class Location(models.Model):
    country = models.ForeignKey(

from smart_selects.db_fields import ChainedManyToManyField

class Publication(models.Model):
    name = models.CharField(max_length=255)

class Writer(models.Model):
    name = models.CharField(max_length=255)
    publications = models.Man

from smart_selects.db_fields import ChainedForeignKey
class Hero(models.Model):
    ....
    race = models.ForeignKey(Race, on_delete=models.CASCADE)
    subrace = ChainedForeignKey(Subrace,
                     

class CouponAdminForm(forms.ModelForm):
    brands = forms.ModelMultipleChoiceField(
                            queryset=Brand.objects.all().order_by('name'),
                            required=False,
                            widget=

from django.core.exceptions import ValidationError


class Match(models.Model):
    championship = models.ForeignKey(Championship)

    team1 = models.ForeignKey(Team)
    team2 = models.ForeignKey(Team)

    score1 = models.PositiveIntege