Question

I have a model class “Place”, which has a field for “state”, and I would like to get a list of querysets grouped by all available distinct states in the DB.

I am currently doing this:

place_list = []
places = Place.objects.distinct('state')
[place_list.append( Place.objects.filter(state=p.state) ) for p in places]

Is there a better aggregate command I could use for optimizing this? What would be the best way to do this?

~ using Python 2.6, Django 1.3.1

Answer 1

from collections import defaultdict

places_by_state = defaultdict(list)
for place in Place.objects.all():
   places_by_state[place.state].append(place)
list_of_places_by_state = places_by_state.values()

That only hits the database once, rather than once per state like your original version (assuming you use all the results), but you end up with a list of lists instead of a list of querysets.