django query aggregation grouping with access to all fields

Question

With models defined like so:

class Athlete(models.Model):
    name = models.CharField()

class Event(models.Model):
    winner = models.ForeignKey(Athlete)
    distance = models.FloatField()

    type_choices = [('LJ', 'Long Jump'), ('HJ', 'High Jump')]
    type = models.CharField(choices=type_choices)

I want to run a query picking out all the events an Athlete has won, grouped by type. I'm currently doing it like so:

athlete = Athlete.objects.get(name='dave')
events_by_type = Events.objects.values('type').annotate(Count('winner')).filter(winner=athlete)

This gives me a dictionary of event types (short versions) and the number of times the athlete has been the winner. However that's all it gives me. If I then want to dig into one of these events to find the distance or even just the verbose type name, I can't.

Am I going about this in the right way? How can I get the events grouped, but also with access to all their fields as well?

Answer 1

You are not getting the event instances because you are querying Event.objects with the values method. This will provide you the data for only the specified fields: https://docs.djangoproject.com/en/dev/ref/models/querysets/#values

Performing this kind of group by with the Django ORM is not straightforward. The proposed solution often is:

q = Events.objects.filter(winner=athlete)
q.query.group_by = ['type']
q.count()

But I'd rather do it with straight python. Maybe something like

athlete = Athlete.objects.get(name='dave')
events = Events.objects.filter(winner=athlete)
won_per_type = defaultdict(list)
for e in events:
    won_per_type(e.type).append(e)