如何通过 django REST 中的方法订购？

Question

I have a simple model like the following:

class Category(models.Model):
    """Class to represent the category of an Item. Like plants, bikes..."""
    name = models.TextField()

    description = models.TextField(null=True)

    color = models.TextField(null=True)

    parent_category = models.ForeignKey(
        'self',
        on_delete=models.SET_NULL,
        null=True,
    )
    class Meta: # pylint: disable=too-few-public-methods
        """Class to represent metadata of the object."""
        # ordering = ['category_name'] <------- I WOULD LIKE THIS SORTING
        ordering = ['parent_category__name', 'name']

    def category_name(self):
        """String for representing the Model object."""
        if self.parent_category:
            return str(self.parent_category.category_name() + " -> " + self.name)

I have not been able to find a solution to sort by a method inside the model like the example that is commented out in the example model.

The results that the two filters I'm using in different steps don't give mt the results I want-

If I have:

Music/Guitar
Music/Piano
Music
Books

It will return:

Music/Guitar
Music/Piano
Books
Music

And what I need is:

Books
Music
Music/Guitar
Music/Piano

It would also be ok to have this in the serializer or be able to choosse the sorting with the parameters in the REST query, but I have not been able to make this work in any possibility.

Answer 1

You can use an annotation that uses Concat to get the parent category name concatenated with name and order by that annotation

from django.db.models.functions import Concat
categories_ordered = Category.objects.annotate(
    joined=Concat('parent_category__name', 'name')
).order_by('joined')

I'm not sure how this will behave if the categories are more than 2 levels deep