django - ordering queryset by a calculated field

Question

I want to have a model with calculated fields that I can apply sorting on. For example, let\'s say that I have the following model:

class Foo(models.Model):
         


        

Answer 1

I find that without the *args and **kwargs in the save method, it returns an error. And as celopes stated, this is only a solution if you don't mind materializing the computed field in the database.

class Foo(models.Model):
    A = models.IntegerField(..)
    B = models.IntegerField(..)
    C = models.ForeignKey(..)
    D = models.IntegerField(..)
    E = models.IntegerField(..)

    def save(self, *args, **kwargs):
        self.D = self.A - self.B
        self.E = self.A - self.C.X
        super(Foo, self).save(*args, **kwargs)

    class Meta:
        ordering = ["E", "D"]