Natural sort on Django Queryset

Question

I am working on a system that lists out a range of products sorted by their product code. The product codes are made up of two letters for the followed by a number, for example EG1.

I currently sort these products by doing a simple

Product.objects.order_by('product_code'),

however as there can be multiple digit product codes (for example EG12), these will come out above ahead of the single digit codes. i.e EG1, EG11, EG12, EG13 ... EG19, EG2, EG20 etc

I know that adding leading zeros to the product codes will fix this (i.e EG01 rather than EG1) but as there is already printed literature and an existing site using EG1 this is not an option.

Is there a way to fix this to show these products in the correct order?

See custom ordering http://stackoverflow.com/a/883641/2614426 — Satevg, Mar 01 '17 at 15:21
Another answer: http://stackoverflow.com/questions/7619554/django-custom-order-by — Satevg, Mar 01 '17 at 15:21

Matthijs Brouns · Accepted Answer · 2019-02-12T16:07:48.557

1

I think the implementation here (https://github.com/nathforge/django-naturalsortfield) should work. The main advantage of this method is that it doesn't do the sorting in python but in the database so it'll perform well even on large datasets, at the cost of some additional storage.

You have to change your model to include a product_code__sort field

class MyModel(models.Model):
    title = models.CharField(max_length=255)
    title_sort = NaturalSortField('title')

where the NaturalSortField is defined as

class NaturalSortField(models.CharField):
    def __init__(self, for_field, **kwargs):
        self.for_field = for_field
        kwargs.setdefault('db_index', True)
        kwargs.setdefault('editable', False)
        kwargs.setdefault('max_length', 255)
        super(NaturalSortField, self).__init__(**kwargs)

    def pre_save(self, model_instance, add):
        return self.naturalize(getattr(model_instance, self.for_field))

    def naturalize(self, string):
        def naturalize_int_match(match):
            return '%08d' % (int(match.group(0)),)

        string = string.lower()
        string = string.strip()
        string = re.sub(r'^the\s+', '', string)
        string = re.sub(r'\d+', naturalize_int_match, string)

        return string

edited Feb 12 '19 at 16:07

answered Mar 01 '17 at 15:24

Matthijs Brouns

2,299
1
27
37

I tried this but have following error on makemigrations: TypeError: __init__() missing 1 required positional argument: 'for_field' – cwhisperer Feb 11 '19 at 16:01
What version of django are you using? – Matthijs Brouns Feb 12 '19 at 11:35
I'm using django 2.1.5 – cwhisperer Feb 12 '19 at 11:46
Could you try passing the name of the original field to the NaturalSortField? I've updated my answer to reflect the required change – Matthijs Brouns Feb 12 '19 at 16:07
1

I added the original field, but still got an error: TypeError: Couldn't reconstruct field house_number_sort on core.Sggl: __init__() missing 1 required positional argument: 'for_field' – cwhisperer Feb 13 '19 at 08:43
This is an old thread but I ran into this same problem today, and forked the repo to submit a fix: https://github.com/niall-byrne/django-naturalsortfield I have submitted a PR to merge. – Niall Byrne Jul 06 '20 at 03:55

score 1 · Answer 2 · answered Nov 19 '19 at 02:38

Try this

def alphanumeric_sort(objects_list, sort_key):
    """ Sort a list of objects by a given key
    This function sort a list of objects by a given
    key common across the objects
    Sorting can be implemented on keys that are either
    alphabets, integers or both
    """
    convert = lambda text: int(text) if text.isdigit() else text
    alphanum_key = lambda key: [
        convert(c) for c in re.split("([0-9]+)", getattr(key, sort_key))
    ]
    return sorted(objects_list, key=alphanum_key)

Natural sort on Django Queryset

2 Answers2

Linked