"""

Many-to-many relationships

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

In this example, an ``Article`` can be published in multiple ``Publication``

objects, and a ``Publication`` has multiple ``Article`` objects.

"""

from django.db import models

class Publication(models.Model):

    title = models.CharField(max_length=30)

    class Meta:

        ordering = ("title",)

    def __str__(self):

        return self.title

class Tag(models.Model):

    id = models.BigAutoField(primary_key=True)

    name = models.CharField(max_length=50)

    def __str__(self):

        return self.name

class NoDeletedArticleManager(models.Manager):

    def get_queryset(self):

        return super().get_queryset().exclude(headline="deleted")

class Article(models.Model):

    headline = models.CharField(max_length=100)

    # Assign a string as name to make sure the intermediary model is

    # correctly created. Refs #20207

    publications = models.ManyToManyField(Publication, name="publications")

    tags = models.ManyToManyField(Tag, related_name="tags")

    authors = models.ManyToManyField("User", through="UserArticle")

    objects = NoDeletedArticleManager()

    class Meta:

        ordering = ("headline",)

    def __str__(self):

        return self.headline

class User(models.Model):

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

    def __str__(self):

        return self.username

class UserArticle(models.Model):

    user = models.ForeignKey(User, models.CASCADE, to_field="username")

    article = models.ForeignKey(Article, models.CASCADE)

# Models to test correct related_name inheritance

class AbstractArticle(models.Model):

    class Meta:

        abstract = True

    publications = models.ManyToManyField(

        Publication, name="publications", related_name="+"

    )

class InheritedArticleA(AbstractArticle):

    pass

class InheritedArticleB(AbstractArticle):

    pass