"""

Many-to-one relationships

To define a many-to-one relationship, use ``ForeignKey()``.

"""

from django.db import models

class Reporter(models.Model):

    first_name = models.CharField(max_length=30)

    last_name = models.CharField(max_length=30)

    email = models.EmailField()

    def __str__(self):

        return "%s %s" % (self.first_name, self.last_name)

class Article(models.Model):

    headline = models.CharField(max_length=100)

    pub_date = models.DateField()

    reporter = models.ForeignKey(Reporter, models.CASCADE)

    class Meta:

        ordering = ("headline",)

    def __str__(self):

        return self.headline

class Country(models.Model):

    id = models.SmallAutoField(primary_key=True)

    name = models.CharField(max_length=50)

class City(models.Model):

    id = models.BigAutoField(primary_key=True)

    country = models.ForeignKey(

        Country, models.CASCADE, related_name="cities", null=True

    )

    name = models.CharField(max_length=50)

class District(models.Model):

    city = models.ForeignKey(City, models.CASCADE, related_name="districts", null=True)

    name = models.CharField(max_length=50)

    def __str__(self):

        return self.name

# If ticket #1578 ever slips back in, these models will not be able to be

# created (the field names being lowercased versions of their opposite classes

# is important here).

class First(models.Model):

    second = models.IntegerField()

class Second(models.Model):

    first = models.ForeignKey(First, models.CASCADE, related_name="the_first")

# Protect against repetition of #1839, #2415 and #2536.

class Third(models.Model):

    name = models.CharField(max_length=20)

    third = models.ForeignKey(

        "self", models.SET_NULL, null=True, related_name="child_set"

    )

class Parent(models.Model):

    name = models.CharField(max_length=20, unique=True)

    bestchild = models.ForeignKey(

        "Child", models.SET_NULL, null=True, related_name="favored_by"

    )

class ParentStringPrimaryKey(models.Model):

    name = models.CharField(primary_key=True, max_length=15)

class Child(models.Model):

    name = models.CharField(max_length=20)

    parent = models.ForeignKey(Parent, models.CASCADE)

class ChildNullableParent(models.Model):

    parent = models.ForeignKey(Parent, models.CASCADE, null=True)

class ChildStringPrimaryKeyParent(models.Model):

    parent = models.ForeignKey(ParentStringPrimaryKey, on_delete=models.CASCADE)

class ToFieldChild(models.Model):

    parent = models.ForeignKey(

        Parent, models.CASCADE, to_field="name", related_name="to_field_children"

    )

# Multiple paths to the same model (#7110, #7125)

class Category(models.Model):

    name = models.CharField(max_length=20)

    def __str__(self):

        return self.name

class Record(models.Model):

    category = models.ForeignKey(Category, models.CASCADE)

class Relation(models.Model):

    left = models.ForeignKey(Record, models.CASCADE, related_name="left_set")

    right = models.ForeignKey(Record, models.CASCADE, related_name="right_set")

    def __str__(self):

        return "%s - %s" % (self.left.category.name, self.right.category.name)

# Test related objects visibility.

class SchoolManager(models.Manager):

    def get_queryset(self):

        return super().get_queryset().filter(is_public=True)

class School(models.Model):

    is_public = models.BooleanField(default=False)

    objects = SchoolManager()

class Student(models.Model):

    school = models.ForeignKey(School, models.CASCADE)