id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
31755	make temporal subtraction work without ExpressionWrapper	Sergey Fedoseev	Sergey Fedoseev	"{{{
class Experiment(models.Model):
    start = models.DateTimeField()
    end = models.DateTimeField()

Experiment.objects.annotate(
    delta=F('end') - F('start') + Value(datetime.timedelta(), output_field=DurationField())
)
}}}
This gives:
{{{
django.core.exceptions.FieldError: Expression contains mixed types: DateTimeField, DurationField. You must set output_field.
}}}

"	Cleanup/optimization	closed	Database layer (models, ORM)	dev	Normal	fixed			Ready for checkin	1	0	0	0	0	0