4. How to order on a field from a related model (with a foreign key)?

You have two models, Category and Hero.

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


class Hero(models.Model):
    # ...
    name = models.CharField(max_length=100)
    category = models.ForeignKey(Category, on_delete=models.CASCADE)

You want to order Hero by category and inside each category by the Hero name. You can do.

Hero.objects.all().order_by(
    'category__name', 'name'
)

Note the double underscore(__ ) in 'category__name'. Using the double undertscore, you can order on a field from a related model.

If you look at the SQL.

SELECT "entities_hero"."id",
       "entities_hero"."name",
       -- more fields
FROM "entities_hero"
INNER JOIN "entities_category" ON ("entities_hero"."category_id" = "entities_category"."id")
ORDER BY "entities_category"."name" ASC,
         "entities_hero"."name" ASC