Django annotate on another distinct field in queryset

Question

I have a model as follows:

class Task(models.Model):
    value= models.IntegerField()
    data = models.CharField(max_length=50, blank=True)

I want to make a query to return the sum of the values for every distinct data. I tried the following but it didn't work:

Task.objects.all().distinct('data').annotate(value = Sum('value'))

I was getting this error:

NotImplementedError: annotate() + distinct(fields) not implemented.

How would you know which values to cosider (from the set of task with identical data)? — Ludwik Trammer
– Ludwik Trammer, Commented Mar 11, 2015 at 19:44
@LudwikTrammer: So u mean to say we cannot achieve this in a single query? DO we need to write 2 queries? — Abhishek
– Abhishek, Commented Mar 11, 2015 at 19:49

Todor · Accepted Answer · 2015-03-11 20:40:47Z

1

Try with values instead of distinct, this will group by data (not sure if this is what you need).

Task.objects.values('data').annotate(Sum('value'))

An attempt with .extra (to select the entire object)

Task.objects.extra(select={'values_sum': "SELECT SUM(values) FROM myapp_task t WHERE t.data = myapp_task.data"})

answered Mar 11, 2015 at 19:49

Todor

16.2k6 gold badges61 silver badges63 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

But values will not return me the whole object right? I am trying to get the entire object. Is there a way to do that?

@RogerFederer will returns only data attribute.

@RogerFederer, checkout my second example.