Django - get distinct dates from timestamp

Question

I\'m trying to filter users by date, but can\'t until I can find the first and last date of users in the db. While I can have my script filter out dups later on, I want to do it

Answer 1

When doing reports on larger datasets itertools.group_by might be too slow. In those cases I make postgres handle the grouping:

truncate_date = connection.ops.date_trunc_sql('day','timestamp')
qs = qs.extra({'date':truncate_date})
return qs.values('date').annotate(Sum('amount')).order_by('date')

Answer 2

I've voted to close this since it's a dup of this question, so here's the answer if you don't want to visit the link, courtesy of nosklo.

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Create a small function to extract just the date: def extract_date(entity): 'extracts the starting date from an entity' return entity.start_time.date()

Then you can use it with itertools.groupby:

from itertools import groupby

entities = Entity.objects.order_by('start_time')
for start_date, group in groupby(entities, key=extract_date):
    do_something_with(start_date, list(group))