Question

I have a vector of three numbers as a name for a model.
i.e. 12-1-120 12-1-139 12-1-9 etc.

I wanted to sort instances of the model in descending order, using Django to display 12-1-139, 12-1-120, 12-1-9.

Except it always acts like a string, hence displaying 12-1-9, 12-1-139, 12-1-120.

I’ve tried using the ‘CommaSeparatedIntegerField’ yet it’s totally useless and still acts the same way.

The only way that I know of, that would technically work, is by having three separate “IntegerField”s and ordering it by the combination, which I think is too impractical.

Any pointers, or am I stuck with this impractical method?

I forgot to mention that I also needed to sometimes call this object using a string and I didn’t want to constantly convert the string to an int so I did it the other way around and stored the bunch of ints into a string using somewhat of a calculated field.

Here’s my basic code:

class MyModelName(models.Model):
    name = models.CharField(max_length=15)
    x = models.IntegerField(max_length=200)
    y = models.IntegerField(max_length=200)
    z = models.IntegerField(max_length=200)

    def save(self, *args, **kwargs):
        self.name = '-'.join([str(self.x), str(self.y), str(self.z)])
        super(MyModelName, self).save(*args, **kwargs)

    class Meta:
        ordering = ["-x","-y","-z"]

Answer 1

Three integer fields is the way to go.

If you want to name your objects that way, you could always add a unicode function to your model…

class Thing(models.Model):
    x = models.IntegerField()
    y = models.IntegerField()
    z = models.IntegerField()

    def __unicode__(self):
        """
            Return a human-readable representation of the object.
        """
        return '-'.join(self.x, self.y, self.z)

https://docs.djangoproject.com/en/dev/ref/models/instances/#unicode

get_or_create example:

s = '12-1-9'
x, y, z = [int(c) for c in s.split('-')]
thing, created = Thing.objects.get_or_create(x=x, y=y, z=z)

custom get or create method

class ThingManager(models.Manager):

    def from_string(s):
        x, y, z = [int(c) for c in s.split('-')]
        obj, created = self.get_or_create(x=x, y=y, z=z)
        return obj, created


class Thing(models.Model):
    objects = ThingManager()
    # Snip


--


my_new_thing, created = Thing.objects.from_string('12-1-9')