Django annotate time delta by hours - django

Question

I have a model as follows:
class WorkTime(models.Model):
person = models.ForeignKey(Person)
entry_date = models.DateField(default=datetime.datetime.now(), verbose_name='date')
start_time = models.TimeField(verbose_name='start')
end_time = models.TimeField(verbose_name='end')
With data as follows:
person, date, start, end
1 01/01/2014 08:00 12:00
1 01/01/2014 13:00 18:00
1 02/01/2014 08:00 12:00
1 02/01/2014 13:00 18:00
1 03/01/2014 08:00 16:00
1 01/02/2014 08:30 12:00
1 01/02/2014 13:00 18:00
2 01/01/2014 09:00 13:00
2 01/01/2014 14:00 18:00
How would one sum up the time delta (i.e. end_time - start_time) and GROUP BY person to show the hours worked by person, as below?
person, hours
1 34:30
2 08:00

Answer 1

I don't know a good way to do this in the ORM. It's pretty straight forward to build a dictionary by iterating through a queryset.
from collections import defaultdict
from datetime import datetime
totals = defaultdict()
work_times = WorkTime.objects.
for work_time in work_times:
totals[work_time.person] += datetime.combine(work_time.entry_date, work_time.end_time) - datetime.combine(work_time.entry_date, work_time.start_time)
# print results
for person, total_time in totals.items():
# total_time will be a timedelta, you can do some more work to return hours and minutes
print person, total_time
Depending on your usage, the performance of this might be good enough.

Answer 2

This has been a while, but maybe someone will stumble upon this.
You can do it this way:
from django.db.models import F, Sum
queryset = queryset.values('person').annotate(sum_delta=Sum(F('end_time')-F('start_time')).order_by('person__id')
This will sum up all timedeltas for each person and you dont have to store extra stuff in the db.