import datetime
import tempfile
import uuid

from django.contrib import admin
from django.contrib.auth.models import User
from django.contrib.contenttypes.fields import GenericForeignKey, GenericRelation
from django.contrib.contenttypes.models import ContentType
from django.core.exceptions import ValidationError
from django.core.files.storage import FileSystemStorage
from django.db import models


class Section(models.Model):
    """
    A simple section that links to articles, to test linking to related items
    in admin views.
    """

    name = models.CharField(max_length=100)

    def __str__(self):
        return self.name

    @property
    def name_property(self):
        """
        A property that simply returns the name. Used to test #24461
        """
        return self.name


class Article(models.Model):
    """
    A simple article to test admin views. Test backwards compatibility.
    """

    title = models.CharField(max_length=100)
    content = models.TextField()
    date = models.DateTimeField()
    section = models.ForeignKey(Section, models.CASCADE, null=True, blank=True)
    another_section = models.ForeignKey(
        Section, models.CASCADE, null=True, blank=True, related_name="+"
    )
    sub_section = models.ForeignKey(
        Section, models.SET_NULL, null=True, blank=True, related_name="+"
    )

    def __str__(self):
        return self.title

    @admin.display(ordering="date", description="")
    def model_year(self):
        return self.date.year

    @admin.display(ordering="-date", description="")
    def model_year_reversed(self):
        return self.date.year

    @property
    @admin.display(ordering="date")
    def model_property_year(self):
        return self.date.year

    @property
    def model_month(self):
        return self.date.month


class Book(models.Model):
    """
    A simple book that has chapters.
    """

    name = models.CharField(max_length=100, verbose_name="¿Name?")

    def __str__(self):
        return self.name


class Promo(models.Model):
    name = models.CharField(max_length=100, verbose_name="¿Name?")
    book = models.ForeignKey(Book, models.CASCADE)
    author = models.ForeignKey(User, models.SET_NULL, blank=True, null=True)

    def __str__(self):
        return self.name


class Chapter(models.Model):
    title = models.CharField(max_length=100, verbose_name="¿Title?")
    content = models.TextField()
    book = models.ForeignKey(Book, models.CASCADE)

    class Meta:
        # Use a utf-8 bytestring to ensure it works (see #11710)
        verbose_name = "¿Chapter?"

    def __str__(self):
        return self.title


class ChapterXtra1(models.Model):
    chap = models.OneToOneField(Chapter, models.CASCADE, verbose_name="¿Chap?")
    xtra = models.CharField(max_length=100, verbose_name="¿Xtra?")
    guest_author = models.ForeignKey(User, models.SET_NULL, blank=True, null=True)

    def __str__(self):
        return "¿Xtra1: %s" % self.xtra


class ChapterXtra2(models.Model):
    chap = models.OneToOneField(Chapter, models.CASCADE, verbose_name="¿Chap?")
    xtra = models.CharField(max_length=100, verbose_name="¿Xtra?")

    def __str__(self):
        return "¿Xtra2: %s" % self.xtra


class RowLevelChangePermissionModel(models.Model):
    name = models.CharField(max_length=100, blank=True)


class CustomArticle(models.Model):
    content = models.TextField()
    date = models.DateTimeField()


class ModelWithStringPrimaryKey(models.Model):
    string_pk = models.CharField(max_length=255, primary_key=True)

    def __str__(self):
        return self.string_pk

    def get_absolute_url(self):
        return "/dummy/%s/" % self.string_pk


class Color(models.Model):
    value = models.CharField(max_length=10)
    warm = models.BooleanField(default=False)

    def __str__(self):
        return self.value


# we replicate Color to register with another ModelAdmin
class Color2(Color):
    class Meta:
        proxy = True


class Thing(models.Model):
    title = models.CharField(max_length=20)
    color = models.ForeignKey(Color, models.CASCADE, limit_choices_to={"warm": True})
    pub_date = models.DateField(blank=True, null=True)

    def __str__(self):
        return self.title


class Actor(models.Model):
    name = models.CharField(max_length=50)
    age = models.IntegerField()
    title = models.CharField(max_length=50, null=True, blank=True)

    def __str__(self):
        return self.name


class Inquisition(models.Model):
    expected = models.BooleanField(default=False)
    leader = models.ForeignKey(Actor, models.CASCADE)
    country = models.CharField(max_length=20)

    def __str__(self):
        return "by %s from %s" % (self.leader, self.country)


class Sketch(models.Model):
    title = models.CharField(max_length=100)
    inquisition = models.ForeignKey(
        Inquisition,
        models.CASCADE,
        limit_choices_to={
            "leader__name": "Palin",
            "leader__age": 27,
            "expected": False,
        },
    )
    defendant0 = models.ForeignKey(
        Actor,
        models.CASCADE,
        limit_choices_to={"title__isnull": False},
        related_name="as_defendant0",
    )
    defendant1 = models.ForeignKey(
        Actor,
        models.CASCADE,
        limit_choices_to={"title__isnull": True},
        related_name="as_defendant1",
    )

    def __str__(self):
        return self.title


def today_callable_dict():
    return {"last_action__gte": datetime.datetime.today()}


def today_callable_q():
    return models.Q(last_action__gte=datetime.datetime.today())


class Character(models.Model):
    username = models.CharField(max_length=100)
    last_action = models.DateTimeField()

    def __str__(self):
        return self.username


class StumpJoke(models.Model):
    variation = models.CharField(max_length=100)
    most_recently_fooled = models.ForeignKey(
        Character,
        models.CASCADE,
        limit_choices_to=today_callable_dict,
        related_name="+",
    )
    has_fooled_today = models.ManyToManyField(
        Character, limit_choices_to=today_callable_q, related_name="+"
    )

    def __str__(self):
        return self.variation


class Fabric(models.Model):
    NG_CHOICES = (
        (
            "Textured",
            (
                ("x", "Horizontal"),
                ("y", "Vertical"),
            ),
        ),
        ("plain", "Smooth"),
    )
    surface = models.CharField(max_length=20, choices=NG_CHOICES)


class Person(models.Model):
    GENDER_CHOICES = (
        (1, "Male"),
        (2, "Female"),
    )
    name = models.CharField(max_length=100)
    gender = models.IntegerField(choices=GENDER_CHOICES)
    age = models.IntegerField(default=21)
    alive = models.BooleanField(default=True)

    def __str__(self):
        return self.name


class Persona(models.Model):
    """
    A simple persona associated with accounts, to test inlining of related
    accounts which inherit from a common accounts class.
    """

    name = models.CharField(blank=False, max_length=80)

    def __str__(self):
        return self.name


class Account(models.Model):
    """
    A simple, generic account encapsulating the information shared by all
    types of accounts.
    """

    username = models.CharField(blank=False, max_length=80)
    persona = models.ForeignKey(Persona, models.CASCADE, related_name="accounts")
    servicename = "generic service"

    def __str__(self):
        return "%s: %s" % (self.servicename, self.username)


class FooAccount(Account):
    """A service-specific account of type Foo."""

    servicename = "foo"


class BarAccount(Account):
    """A service-specific account of type Bar."""

    servicename = "bar"


class Subscriber(models.Model):
    name = models.CharField(blank=False, max_length=80)
    email = models.EmailField(blank=False, max_length=175)

    def __str__(self):
        return "%s (%s)" % (self.name, self.email)


class ExternalSubscriber(Subscriber):
    pass


class OldSubscriber(Subscriber):
    pass


class Media(models.Model):
    name = models.CharField(max_length=60)


class Podcast(Media):
    release_date = models.DateField()

    class Meta:
        ordering = ("release_date",)  # overridden in PodcastAdmin


class Vodcast(Media):
    media = models.OneToOneField(
        Media, models.CASCADE, primary_key=True, parent_link=True
    )
    released = models.BooleanField(default=False)


class Parent(models.Model):
    name = models.CharField(max_length=128)

    def clean(self):
        if self.name == "_invalid":
            raise ValidationError("invalid")


class Child(models.Model):
    parent = models.ForeignKey(Parent, models.CASCADE, editable=False)
    name = models.CharField(max_length=30, blank=True)

    def clean(self):
        if self.name == "_invalid":
            raise ValidationError("invalid")


class PKChild(models.Model):
    """
    Used to check autocomplete to_field resolution when ForeignKey is PK.
    """

    parent = models.ForeignKey(Parent, models.CASCADE, primary_key=True)
    name = models.CharField(max_length=128)

    class Meta:
        ordering = ["parent"]

    def __str__(self):
        return self.name


class Toy(models.Model):
    child = models.ForeignKey(PKChild, models.CASCADE)


class EmptyModel(models.Model):
    def __str__(self):
        return "Primary key = %s" % self.id


temp_storage = FileSystemStorage(tempfile.mkdtemp())


class Gallery(models.Model):
    name = models.CharField(max_length=100)


class Picture(models.Model):
    name = models.CharField(max_length=100)
    image = models.FileField(storage=temp_storage, upload_to="test_upload")
    gallery = models.ForeignKey(Gallery, models.CASCADE, related_name="pictures")


class Language(models.Model):
    iso = models.CharField(max_length=5, primary_key=True)
    name = models.CharField(max_length=50)
    english_name = models.CharField(max_length=50)
    shortlist = models.BooleanField(default=False)

    def __str__(self):
        return self.iso

    class Meta:
        ordering = ("iso",)


# a base class for Recommender and Recommendation
class Title(models.Model):
    pass


class TitleTranslation(models.Model):
    title = models.ForeignKey(Title, models.CASCADE)
    text = models.CharField(max_length=100)


class Recommender(Title):
    pass


class Recommendation(Title):
    the_recommender = models.ForeignKey(Recommender, models.CASCADE)


class Collector(models.Model):
    name = models.CharField(max_length=100)


class Widget(models.Model):
    owner = models.ForeignKey(Collector, models.CASCADE)
    name = models.CharField(max_length=100)


class DooHickey(models.Model):
    code = models.CharField(max_length=10, primary_key=True)
    owner = models.ForeignKey(Collector, models.CASCADE)
    name = models.CharField(max_length=100)


class Grommet(models.Model):
    code = models.AutoField(primary_key=True)
    owner = models.ForeignKey(Collector, models.CASCADE)
    name = models.CharField(max_length=100)


class Whatsit(models.Model):
    index = models.IntegerField(primary_key=True)
    owner = models.ForeignKey(Collector, models.CASCADE)
    name = models.CharField(max_length=100)


class Doodad(models.Model):
    name = models.CharField(max_length=100)


class FancyDoodad(Doodad):
    owner = models.ForeignKey(Collector, models.CASCADE)
    expensive = models.BooleanField(default=True)


class Category(models.Model):
    collector = models.ForeignKey(Collector, models.CASCADE)
    order = models.PositiveIntegerField()

    class Meta:
        ordering = ("order",)

    def __str__(self):
        return "%s:o%s" % (self.id, self.order)


def link_posted_default():
    return datetime.date.today() - datetime.timedelta(days=7)


class Link(models.Model):
    posted = models.DateField(default=link_posted_default)
    url = models.URLField()
    post = models.ForeignKey("Post", models.CASCADE)
    readonly_link_content = models.TextField()


class PrePopulatedPost(models.Model):
    title = models.CharField(max_length=100)
    published = models.BooleanField(default=False)
    slug = models.SlugField()


class PrePopulatedSubPost(models.Model):
    post = models.ForeignKey(PrePopulatedPost, models.CASCADE)
    subtitle = models.CharField(max_length=100)
    subslug = models.SlugField()


class Post(models.Model):
    title = models.CharField(
        max_length=100, help_text="Some help text for the title (with Unicode ŠĐĆŽćžšđ)"
    )
    content = models.TextField(
        help_text="Some help text for the content (with Unicode ŠĐĆŽćžšđ)"
    )
    readonly_content = models.TextField()
    posted = models.DateField(
        default=datetime.date.today,
        help_text="Some help text for the date (with Unicode ŠĐĆŽćžšđ)",
    )
    public = models.BooleanField(null=True, blank=True)

    def awesomeness_level(self):
        return "Very awesome."


# Proxy model to test overridden fields attrs on Post model so as not to
# interfere with other tests.
class FieldOverridePost(Post):
    class Meta:
        proxy = True


class Gadget(models.Model):
    name = models.CharField(max_length=100)

    def __str__(self):
        return self.name


class Villain(models.Model):
    name = models.CharField(max_length=100)

    def __str__(self):
        return self.name


class SuperVillain(Villain):
    pass


class FunkyTag(models.Model):
    "Because we all know there's only one real use case for GFKs."
    name = models.CharField(max_length=25)
    content_type = models.ForeignKey(ContentType, models.CASCADE)
    object_id = models.PositiveIntegerField()
    content_object = GenericForeignKey("content_type", "object_id")

    def __str__(self):
        return self.name


class Plot(models.Model):
    name = models.CharField(max_length=100)
    team_leader = models.ForeignKey(Villain, models.CASCADE, related_name="lead_plots")
    contact = models.ForeignKey(Villain, models.CASCADE, related_name="contact_plots")
    tags = GenericRelation(FunkyTag)

    def __str__(self):
        return self.name


class PlotDetails(models.Model):
    details = models.CharField(max_length=100)
    plot = models.OneToOneField(Plot, models.CASCADE, null=True, blank=True)

    def __str__(self):
        return self.details


class PlotProxy(Plot):
    class Meta:
        proxy = True


class SecretHideout(models.Model):
    """Secret! Not registered with the admin!"""

    location = models.CharField(max_length=100)
    villain = models.ForeignKey(Villain, models.CASCADE)

    def __str__(self):
        return self.location


class SuperSecretHideout(models.Model):
    """Secret! Not registered with the admin!"""

    location = models.CharField(max_length=100)
    supervillain = models.ForeignKey(SuperVillain, models.CASCADE)

    def __str__(self):
        return self.location


class Bookmark(models.Model):
    name = models.CharField(max_length=60)
    tag = GenericRelation(FunkyTag, related_query_name="bookmark")

    def __str__(self):
        return self.name


class CyclicOne(models.Model):
    name = models.CharField(max_length=25)
    two = models.ForeignKey("CyclicTwo", models.CASCADE)

    def __str__(self):
        return self.name


class CyclicTwo(models.Model):
    name = models.CharField(max_length=25)
    one = models.ForeignKey(CyclicOne, models.CASCADE)

    def __str__(self):
        return self.name


class Topping(models.Model):
    name = models.CharField(max_length=20)

    def __str__(self):
        return self.name


class Pizza(models.Model):
    name = models.CharField(max_length=20)
    toppings = models.ManyToManyField("Topping", related_name="pizzas")


# Pizza's ModelAdmin has readonly_fields = ['toppings'].
# toppings is editable for this model's admin.
class ReadablePizza(Pizza):
    class Meta:
        proxy = True


# No default permissions are created for this model and both name and toppings
# are readonly for this model's admin.
class ReadOnlyPizza(Pizza):
    class Meta:
        proxy = True
        default_permissions = ()


class Album(models.Model):
    owner = models.ForeignKey(User, models.SET_NULL, null=True, blank=True)
    title = models.CharField(max_length=30)


class Song(models.Model):
    name = models.CharField(max_length=20)
    album = models.ForeignKey(Album, on_delete=models.RESTRICT)

    def __str__(self):
        return self.name


class Employee(Person):
    code = models.CharField(max_length=20)

    class Meta:
        ordering = ["name"]


class WorkHour(models.Model):
    datum = models.DateField()
    employee = models.ForeignKey(Employee, models.CASCADE)


class Manager(Employee):
    """
    A multi-layer MTI child.
    """

    pass


class Bonus(models.Model):
    recipient = models.ForeignKey(Manager, on_delete=models.CASCADE)


class Question(models.Model):
    big_id = models.BigAutoField(primary_key=True)
    question = models.CharField(max_length=20)
    posted = models.DateField(default=datetime.date.today)
    expires = models.DateTimeField(null=True, blank=True)
    related_questions = models.ManyToManyField("self")
    uuid = models.UUIDField(default=uuid.uuid4, unique=True)

    def __str__(self):
        return self.question


class Answer(models.Model):
    question = models.ForeignKey(Question, models.PROTECT)
    question_with_to_field = models.ForeignKey(
        Question,
        models.SET_NULL,
        blank=True,
        null=True,
        to_field="uuid",
        related_name="uuid_answers",
        limit_choices_to=~models.Q(question__istartswith="not"),
    )
    related_answers = models.ManyToManyField("self")
    answer = models.CharField(max_length=20)

    def __str__(self):
        return self.answer


class Answer2(Answer):
    class Meta:
        proxy = True


class Reservation(models.Model):
    start_date = models.DateTimeField()
    price = models.IntegerField()


class FoodDelivery(models.Model):
    DRIVER_CHOICES = (
        ("bill", "Bill G"),
        ("steve", "Steve J"),
    )
    RESTAURANT_CHOICES = (
        ("indian", "A Taste of India"),
        ("thai", "Thai Pography"),
        ("pizza", "Pizza Mama"),
    )
    reference = models.CharField(max_length=100)
    driver = models.CharField(max_length=100, choices=DRIVER_CHOICES, blank=True)
    restaurant = models.CharField(
        max_length=100, choices=RESTAURANT_CHOICES, blank=True
    )

    class Meta:
        unique_together = (("driver", "restaurant"),)


class CoverLetter(models.Model):
    author = models.CharField(max_length=30)
    date_written = models.DateField(null=True, blank=True)

    def __str__(self):
        return self.author


class Paper(models.Model):
    title = models.CharField(max_length=30)
    author = models.CharField(max_length=30, blank=True, null=True)


class ShortMessage(models.Model):
    content = models.CharField(max_length=140)
    timestamp = models.DateTimeField(null=True, blank=True)


class Telegram(models.Model):
    title = models.CharField(max_length=30)
    date_sent = models.DateField(null=True, blank=True)

    def __str__(self):
        return self.title


class Story(models.Model):
    title = models.CharField(max_length=100)
    content = models.TextField()


class OtherStory(models.Model):
    title = models.CharField(max_length=100)
    content = models.TextField()


class ComplexSortedPerson(models.Model):
    name = models.CharField(max_length=100)
    age = models.PositiveIntegerField()
    is_employee = models.BooleanField(null=True)


class PluggableSearchPerson(models.Model):
    name = models.CharField(max_length=100)
    age = models.PositiveIntegerField()


class PrePopulatedPostLargeSlug(models.Model):
    """
    Regression test for #15938: a large max_length for the slugfield must not
    be localized in prepopulated_fields_js.html or it might end up breaking
    the JavaScript (ie, using THOUSAND_SEPARATOR ends up with maxLength=1,000)
    """

    title = models.CharField(max_length=100)
    published = models.BooleanField(default=False)
    # `db_index=False` because MySQL cannot index large CharField (#21196).
    slug = models.SlugField(max_length=1000, db_index=False)


class AdminOrderedField(models.Model):
    order = models.IntegerField()
    stuff = models.CharField(max_length=200)


class AdminOrderedModelMethod(models.Model):
    order = models.IntegerField()
    stuff = models.CharField(max_length=200)

    @admin.display(ordering="order")
    def some_order(self):
        return self.order


class AdminOrderedAdminMethod(models.Model):
    order = models.IntegerField()
    stuff = models.CharField(max_length=200)


class AdminOrderedCallable(models.Model):
    order = models.IntegerField()
    stuff = models.CharField(max_length=200)


class Report(models.Model):
    title = models.CharField(max_length=100)

    def __str__(self):
        return self.title


class MainPrepopulated(models.Model):
    name = models.CharField(max_length=100)
    pubdate = models.DateField()
    status = models.CharField(
        max_length=20,
        choices=(("option one", "Option One"), ("option two", "Option Two")),
    )
    slug1 = models.SlugField(blank=True)
    slug2 = models.SlugField(blank=True)
    slug3 = models.SlugField(blank=True, allow_unicode=True)


class RelatedPrepopulated(models.Model):
    parent = models.ForeignKey(MainPrepopulated, models.CASCADE)
    name = models.CharField(max_length=75)
    fk = models.ForeignKey("self", models.CASCADE, blank=True, null=True)
    m2m = models.ManyToManyField("self", blank=True)
    pubdate = models.DateField()
    status = models.CharField(
        max_length=20,
        choices=(("option one", "Option One"), ("option two", "Option Two")),
    )
    slug1 = models.SlugField(max_length=50)
    slug2 = models.SlugField(max_length=60)


class UnorderedObject(models.Model):
    """
    Model without any defined `Meta.ordering`.
    Refs #16819.
    """

    name = models.CharField(max_length=255)
    bool = models.BooleanField(default=True)


class UndeletableObject(models.Model):
    """
    Model whose show_delete in admin change_view has been disabled
    Refs #10057.
    """

    name = models.CharField(max_length=255)


class UnchangeableObject(models.Model):
    """
    Model whose change_view is disabled in admin
    Refs #20640.
    """


class UserMessenger(models.Model):
    """
    Dummy class for testing message_user functions on ModelAdmin
    """


class Simple(models.Model):
    """
    Simple model with nothing on it for use in testing
    """


class Choice(models.Model):
    choice = models.IntegerField(
        blank=True,
        null=True,
        choices=((1, "Yes"), (0, "No"), (None, "No opinion")),
    )


class ParentWithDependentChildren(models.Model):
    """
    Issue #20522
    Model where the validation of child foreign-key relationships depends
    on validation of the parent
    """

    some_required_info = models.PositiveIntegerField()
    family_name = models.CharField(max_length=255, blank=False)


class DependentChild(models.Model):
    """
    Issue #20522
    Model that depends on validation of the parent class for one of its
    fields to validate during clean
    """

    parent = models.ForeignKey(ParentWithDependentChildren, models.CASCADE)
    family_name = models.CharField(max_length=255)


class _Manager(models.Manager):
    def get_queryset(self):
        return super().get_queryset().filter(pk__gt=1)


class FilteredManager(models.Model):
    def __str__(self):
        return "PK=%d" % self.pk

    pk_gt_1 = _Manager()
    objects = models.Manager()


class EmptyModelVisible(models.Model):
    """See ticket #11277."""


class EmptyModelHidden(models.Model):
    """See ticket #11277."""


class EmptyModelMixin(models.Model):
    """See ticket #11277."""


class State(models.Model):
    name = models.CharField(max_length=100, verbose_name="State verbose_name")


class City(models.Model):
    state = models.ForeignKey(State, models.CASCADE)
    name = models.CharField(max_length=100, verbose_name="City verbose_name")

    def get_absolute_url(self):
        return "/dummy/%s/" % self.pk


class Restaurant(models.Model):
    city = models.ForeignKey(City, models.CASCADE)
    name = models.CharField(max_length=100)

    def get_absolute_url(self):
        return "/dummy/%s/" % self.pk


class Worker(models.Model):
    work_at = models.ForeignKey(Restaurant, models.CASCADE)
    name = models.CharField(max_length=50)
    surname = models.CharField(max_length=50)


# Models for #23329
class ReferencedByParent(models.Model):
    name = models.CharField(max_length=20, unique=True)


class ParentWithFK(models.Model):
    fk = models.ForeignKey(
        ReferencedByParent,
        models.CASCADE,
        to_field="name",
        related_name="hidden+",
    )


class ChildOfReferer(ParentWithFK):
    pass


# Models for #23431
class InlineReferer(models.Model):
    pass


class ReferencedByInline(models.Model):
    name = models.CharField(max_length=20, unique=True)


class InlineReference(models.Model):
    referer = models.ForeignKey(InlineReferer, models.CASCADE)
    fk = models.ForeignKey(
        ReferencedByInline,
        models.CASCADE,
        to_field="name",
        related_name="hidden+",
    )


class Recipe(models.Model):
    rname = models.CharField(max_length=20, unique=True)


class Ingredient(models.Model):
    iname = models.CharField(max_length=20, unique=True)
    recipes = models.ManyToManyField(Recipe, through="RecipeIngredient")


class RecipeIngredient(models.Model):
    ingredient = models.ForeignKey(Ingredient, models.CASCADE, to_field="iname")
    recipe = models.ForeignKey(Recipe, models.CASCADE, to_field="rname")


# Model for #23839
class NotReferenced(models.Model):
    # Don't point any FK at this model.
    pass


# Models for #23934
class ExplicitlyProvidedPK(models.Model):
    name = models.IntegerField(primary_key=True)


class ImplicitlyGeneratedPK(models.Model):
    name = models.IntegerField(unique=True)


# Models for #25622
class ReferencedByGenRel(models.Model):
    content_type = models.ForeignKey(ContentType, on_delete=models.CASCADE)
    object_id = models.PositiveIntegerField()
    content_object = GenericForeignKey("content_type", "object_id")


class GenRelReference(models.Model):
    references = GenericRelation(ReferencedByGenRel)


class ParentWithUUIDPK(models.Model):
    id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
    title = models.CharField(max_length=100)

    def __str__(self):
        return str(self.id)


class RelatedWithUUIDPKModel(models.Model):
    parent = models.ForeignKey(
        ParentWithUUIDPK, on_delete=models.SET_NULL, null=True, blank=True
    )


class Author(models.Model):
    pass


class Authorship(models.Model):
    book = models.ForeignKey(Book, models.CASCADE)
    author = models.ForeignKey(Author, models.CASCADE)


class UserProxy(User):
    """Proxy a model with a different app_label."""

    class Meta:
        proxy = True


class ReadOnlyRelatedField(models.Model):
    chapter = models.ForeignKey(Chapter, models.CASCADE)
    language = models.ForeignKey(Language, models.CASCADE)
    user = models.ForeignKey(User, models.CASCADE)


class Héllo(models.Model):
    pass


class Box(models.Model):
    title = models.CharField(max_length=100)
    next_box = models.ForeignKey(
        "self", null=True, on_delete=models.SET_NULL, blank=True
    )
    next_box = models.ForeignKey(
        "self", null=True, on_delete=models.SET_NULL, blank=True
    )


class Country(models.Model):
    NORTH_AMERICA = "North America"
    SOUTH_AMERICA = "South America"
    EUROPE = "Europe"
    ASIA = "Asia"
    OCEANIA = "Oceania"
    ANTARCTICA = "Antarctica"

    CONTINENT_CHOICES = [
        (NORTH_AMERICA, NORTH_AMERICA),
        (SOUTH_AMERICA, SOUTH_AMERICA),
        (EUROPE, EUROPE),
        (ASIA, ASIA),
        (OCEANIA, OCEANIA),
        (ANTARCTICA, ANTARCTICA),
    ]
    name = models.CharField(max_length=80)
    continent = models.CharField(max_length=13, choices=CONTINENT_CHOICES)

    def __str__(self):
        return self.name


class Traveler(models.Model):
    born_country = models.ForeignKey(Country, models.CASCADE)
    living_country = models.ForeignKey(
        Country, models.CASCADE, related_name="living_country_set"
    )
    favorite_country_to_vacation = models.ForeignKey(
        Country,
        models.CASCADE,
        related_name="favorite_country_to_vacation_set",
        limit_choices_to={"continent": Country.ASIA},
    )