Increment of duration field not works properly

[Alex Zaitsev]

I have a duration field in some model:

My(models.Model):
   ...
   duration = models.DurationField(default=timedelta(seconds=0))

and I try to increment durations via F expression:

obj.duration = F('duration') + (now - some_other_datetime)

as a result, we have a value of the following format in the database: 0:18:30.233251 instead of a big integer one. So this makes that instance of model completely unusable, any attempt of access raise an exception: TypeError: unsupported type for timedelta microseconds component: str

[Mariusz Felisiak]

Duplicate of #28925, fixed in dd5aa8cb5ffc0a89c4b9b8dee45c1c919d203489 (Django 3.2+).