Is there a way to make this query work with Django?
stage = Task.objects.filter(id = input_stage.id)\
.update(start_date = max(data.get('start_date'), F('start_date')),
finish_date = max(data.get('finish_date'), F('finish_date')))
Now I get an error:
TypeError: '>' not supported between instances of 'F' and 'datetime.date'
The max between two fields in a database is in Django the Greatest [Django-doc], so the query should read something like:
from django.db.models import F, Value
from django.db.models.functions import Greatest
Task.objects.filter(
id=input_stage.id
).update(
start_date=Greatest(Value(data.get('start_date')), F('start_date')),
finish_date=Greatest(Value(data.get('finish_date')), F('finish_date'))
)You also might want to convert the data.get('start_date'), etc. to date objects.
Mind that a .update(…) [django-doc] does not return a QuerySet, but:
(...) and returns the number of rows matched (which may not be equal to the number of rows updated if some rows already have the new value).
Value or not using it?Value given the fields contain a value, and not a field name, since some of these database functions tend to pick the fieldname. So I think Value(..) is at least safer (although at the moment I can not test it). If you however data.get('start_date') contains the field name, then it should be an F(..).data is just a dict with date.