[Answered ]-Django aggregate for multiple days

.values() can be used to group by date, so you will only get unique dates together with the sum of length fields via .annotate():

>>> from django.db.models import Sum
>>> MyModel.objects.values('date').annotate(total_length=Sum('length'))

From docs:

When .values() clause is used to constrain the columns that are returned in the result set, the method for evaluating annotations is slightly different. Instead of returning an annotated result for each result in the original QuerySet, the original results are grouped according to the unique combinations of the fields specified in the .values() clause.

Hope this helps.