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Conditional order by in django's ORM
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| """ | |
| 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() | |
| ) |
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