Snippets by mawi

Sophisticated order_by sorting

I wanted to sort a CharField which consists of digits in a different way. This field is a matricle number field (some kind of registration number for students. They have matricle numbers in the format YYxxxxxx - which means "YY" are the last two digits of the year they started studying.) So I wanted to sort them in a way that they appear like this: 5000000, 5000001, ... , 9999998, 9999999, 0000000, 0000001, ... , 1200000, ... , 4999999 Took me some time to find out how to do this efficiently in PostgreSQL, and so I thought I'd share it here. The important stuff is in the model "Candidate" to use a special "objects" object manager which uses a special QuerySet as well. Here lies the "magic": If there is a ordering required that contains "mnr", then a special on-the-fly calculated field will be added to the queryset called "mnr_specialsorted". Now it is possible to do things like `Candidate.objects.filter( firstname__contains="Pony" ).exclude( lastname__contains="Java" ).order_by("lastname", "-mnr")` For other database engines you might want to change the MNR_SORTER variable to fit your needs.