Conditional order by in django's ORM

conditional_orderby.py

"""
    Some table has two Date fields: expiredate and SALexpiredate
    Both fields can be null
    when SALexpiredate is not null, overrides expiredate
    when ordering:
        if SALexpiredate is not null, that field needs to be used
        otherwise fallback to use expiredate
"""

from django.db.models import DateField, Case, When, F

queryset.annotate(
    expiredate_salexpiredate=Case(
        When(salexpiredate__isnull=False, then=F('salexpiredate')),
        default=F('expiredate'),
        output_field=DateField(),
    ),
).order_by('-expiredate_salexpiredate')


"""
    This is a simpler approach for the same problem I didn't know I could do.
    I think that this is far better, but the previous could be useful in some use cases.
"""
from django.db.models.functions import Coalesce

queryset.order_by(
    Coalesce(
        F('salexpiredate'),
        F('expiredate')
    ).desc()
)

Thanks for this example. It's worth noting that Coalesce is great when you want to choose the first non-null value. If any other conditions should be met (e.g. comparing datetimes), your first approach is the solution, adding queries inside the When() block as needed.