Django: ordering numerical value with order_by

Question

I\'m in a situation where I must output a quite large list of objects by a CharField used to store street addresses.

My problem is, that obviously the data is ordere

Answer 1

Django is trying to deprecate the extra() method, but has introduced Cast() in v1.10. In sqlite (at least), CAST can take a value such as 10a and will cast it to the integer 10, so you can do:

from django.db.models import IntegerField
from django.db.models.functions import Cast

MyModel.objects.annotate(
    my_integer_field=Cast('my_char_field', IntegerField())
).order_by('my_integer_field', 'my_char_field')

which will return objects sorted by the street number first numerically, then alphabetically, e.g. ...14, 15a, 15b, 16, 16a, 17...

Answer 2

Great tip! It works for me! :) That's my code:

revisioned_objects = revisioned_objects.extra(select={'casted_object_id': 'CAST(object_id AS INTEGER)'}).extra(order_by = ['casted_object_id'])

Answer 3

I was looking for a way to sort the numeric chars in a CharField and my search led me here. The name fields in my objects are CC Licenses, e.g., 'CC BY-NC 4.0'.

Since extra() is going to be deprecated, I was able to do it this way:

MyObject.objects.all()
    .annotate(sorting_int=Cast(Func(F('name'), Value('\D'), Value(''), Value('g'), function='regexp_replace'), IntegerField()))
    .order_by('-sorting_int')

Thus, MyObject with name='CC BY-NC 4.0' now has sorting_int=40.

Answer 4

In my case i have a CharField with a name field, which has mixed (int+string) values, for example. "a1", "f65", "P", "55" e.t.c ..

Solved the issue by using the sql cast (tested with postgres & mysql), first, I try to sort by the casted integer value, and then by the original value of the name field.

parking_slots = ParkingSlot.objects.all().extra(
        select={'num_from_name': 'CAST(name AS INTEGER)'}
    ).order_by('num_from_name', 'name')

This way, in any case, the correct sorting works for me.

Answer 5

The problem you're up against is quite similar to how filenames get ordered when sorting by filename. There, you want "2 Foo.mp3" to appear before "12 Foo.mp3".

A common approach is to "normalize" numbers to expanding to a fixed number of digits, and then sorting based on the normalized form. That is, for purposes of sorting, "2 Foo.mp3" might expand to "0000000002 Foo.mp3".

Django won't help you here directly. You can either add a field to store the "normalized" address, and have the database order_by that, or you can do a custom sort in your view (or in a helper that your view uses) on address records before handing the list of records to a template.

Answer 6

In case you need to sort version numbers consisting of multiple numbers separated by a dot (e.g. 1.9.0, 1.10.0), here is a postgres-only solution:

class VersionRecordManager(models.Manager):

    def get_queryset(self):
        return super().get_queryset().extra(
            select={
                'natural_version': "string_to_array(version, '.')::int[]",
            },
        )

    def available_versions(self):
        return self.filter(available=True).order_by('-natural_version')

    def last_stable(self):
        return self.available_versions().filter(stable=True).first()

class VersionRecord(models.Model):
    objects = VersionRecordManager()
    version = models.CharField(max_length=64, db_index=True)
    available = models.BooleanField(default=False, db_index=True)
    stable = models.BooleanField(default=False, db_index=True)

In case you want to allow non-numeric characters (e.g. 0.9.0 beta, 2.0.0 stable):

def get_queryset(self):
    return super().get_queryset().extra(
        select={
            'natural_version':
                "string_to_array(                     "  
                "   regexp_replace(                   "  # Remove everything except digits
                "       version, '[^\d\.]+', '', 'g'  "  # and dots, then split string into
                "   ), '.'                            "  # an array of integers.
                ")::int[]                             "
        }
    )