from django.db import models
from django.db.models.expressions import Value
from django.contrib.auth.models import User


class Person(models.Model):
    name = models.CharField(max_length=100)
    creator = models.ForeignKey(User, models.CASCADE, null=True)
    creation_date = models.DateField(auto_now=True)

def run():
    admin = User.objects.create(username="admin")
    Person.objects.create(creator=admin, name="Violet")
    qs1 = Person.objects.all()
    qs2 = Person.objects.annotate(creator__username=Value(1))
    qs3 = Person.objects.annotate(creation_date__year=Value(1))
    # raises ValueError
    # qs4 = Person.objects.annotate(creator=Value(1))
    # qs5 = Person.objects.annotate(creation_date=Value(1))

    # lookup without shadowing
    print(qs1.values("creator__username"))
    # lookup with shadowing
    print(qs2.values("creator__username"))
    # transform without shadowing
    print(qs1.values("creation_date__year"))
    # transform with shadowing
    print(qs3.values("creation_date__year"))