"""
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