python - Django QuerySet Custom Ordering by ID

Question

Given a list of ids/pks, I'd like to generate a QuerySet of objects ordered by the index in the list.

Normally I'd begin with:

pk_list = [5, 9, 2, 14]
queryset = MyModel.objects.filter(pk__in=pk_list)

This of course returns the objects, but in the order of the models meta ordering property, and I wish to get the records in the order of the pks in pk_list.

The end result has to be one QuerySet object (not a list), as I wish to pass the ordered QuerySet to Django's ModelMultipleChoiceField form field.

Answer 1

There isn't a built-in way to do this.

If you're using MySQL, you can use that database's FIELD() function to set up a custom ordering sequence on your model, and sort by that. This would work:

pk_list = [5, 9, 2, 14]
ordering = 'FIELD(`id`, %s)' % ','.join(str(id) for id in pk_list)
queryset = MyModel.objects.filter(pk__in=[pk_list]).extra(
               select={'ordering': ordering}, order_by=('ordering',))