Django order_by specific order

Question

Is it possible to replicate this kind of specific sql ordering in the django ORM:

order by

(case

    when id = 5 then 1

    when id = 2 then 2

    when id = 3 then 3

    when id = 1 then 4

    when id = 4 then 5

end) asc

?

Answer 1

You could do it w/ extra() or more plain raw(), but they can not work well w/ more complex situation.

qs.extra(select={'o':'(case when id=5 then 1 when id=2 then 2 when id=3 then 3 when id=1 then 4 when id=4 then 5 end)', order_by='o'}

YourModel.raw('select ... order by (case ...)')

For your code, condition set is very limited, you could sort in Python easily.

Answer 2

Since Django 1.8 you have Conditional Expressions so using extra is not necessary anymore.

from django.db.models import Case, When, Value, IntegerField

SomeModel.objects.annotate(
    custom_order=Case(
        When(id=5, then=Value(1)),
        When(id=2, then=Value(2)),
        When(id=3, then=Value(3)),
        When(id=1, then=Value(4)),
        When(id=4, then=Value(5)),
        output_field=IntegerField(),
    )
).order_by('custom_order')

Answer 3

It is possible. Since Djnago 1.8 you can do in this way from django.db.models import Case, When

ids = [5, 2, 3, 1, 4]
order = Case(*[When(id=id, then=pos) for pos, id in enumerate(ids)])
queryset = MyModel.objects.filter(id__in=ids).order_by(order)