Get objects created in last 30 days, for each past day

items = Foo.objects.filter(createdate__lte=datetime.datetime.today(), createdate__gt=datetime.datetime.today()-datetime.timedelta(days=30)).\
    values('createdate').annotate(count=Count('id'))

This will (1) filter results to contain the last 30 days, (2) select just the createdate field and (3) count the id's, grouping by all selected fields (i.e. createdate). This will return a list of dictionaries of the format:

[
    {'createdate': <datetime.date object>, 'count': <int>},
    {'createdate': <datetime.date object>, 'count': <int>},
    ...
]

EDIT:

I don't believe there's a way to get all dates, even those with count == 0, with just SQL. You'll have to insert each missing date through python code, e.g.:

import datetime

# needed to use .append() later on
items = list(items)

dates = [x.get('createdate') for x in items]

for d in (datetime.datetime.today() - datetime.timedelta(days=x) for x in range(0,30)):
    if d not in dates:
        items.append({'createdate': d, 'count': 0})