#24793: Subtracting DateTime fields in a query expression should use timediff
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Reporter: sparkyb | Owner: nobody
Type: Uncategorized | Status: new
Component: Database layer | Version: 1.8
(models, ORM) | Keywords: datetime duration
Severity: Normal | expression
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
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If I have a model with start and end DateTime fields, I'd like to be able
to annotate a query with the duration. For instance, with the model
{{{
class Event(Model):
start_time = DateTimeField()
end_time = DateTimeField()
}}}
I want to be able to do the following query:
{{{Event.objects.annotate(duration=ExpressionWrapper(F('end_time')-F('start_time'),output_field=DurationField()))}}}.
However this yields and incorrect result. At least in MySQL, the proper
SQL is {{{timediff(end_time,start_time) as duration}}}. I have not found
an alternate way to do this with Django's ORM without writing SQL.
--
Ticket URL: <https://code.djangoproject.com/ticket/24793>
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