"""

Multiple many-to-many relationships between the same two tables

In this example, an ``Article`` can have many "primary" ``Category`` objects

and many "secondary" ``Category`` objects.

Set ``related_name`` to designate what the reverse relationship is called.

"""

from django.db import models

class Category(models.Model):

    name = models.CharField(max_length=20)

    class Meta:

        ordering = ("name",)

    def __str__(self):

        return self.name

class Article(models.Model):

    headline = models.CharField(max_length=50)

    pub_date = models.DateTimeField()

    primary_categories = models.ManyToManyField(

        Category, related_name="primary_article_set"

    )

    secondary_categories = models.ManyToManyField(

        Category, related_name="secondary_article_set"

    )

    class Meta:

        ordering = ("pub_date",)

    def __str__(self):

        return self.headline