how to group by with annotate in django?

Question

I tried absolutely everything with values().annotate() or aggregate(), or by following tutorials with Subquery I cant get what I want, let me explain:

There is what I get with QuizzUserItem.objects.filter(examuser=user_exam).values('item__question', 'item')

{'item': 759, 'item__question': 429}
{'item': 762, 'item__question': 430}
{'item': 763, 'item__question': 430}
{'item': 767, 'item__question': 431}

What I want is to group by item__question and get this result:

{'item': 759, 'item__question': 429}
{'item': 762,763 'item__question': 430}
{'item': 767, 'item__question': 431}

I start to think there is absolutely no way:/

---

What I tried:

QuizzUserItem.objects.filter(examuser=user_exam).values('item__question','item').annotate(items_number=Count('item__question'))

I got:

{'item': 759, 'item__question': 429, 'items_number': 1}
{'item': 762, 'item__question': 430, 'items_number': 1}
{'item': 763, 'item__question': 430, 'items_number': 1}
{'item': 767, 'item__question': 431, 'items_number': 1}

or

QuizzUserItem.objects.filter(examuser=user_exam).values('item__question').annotate(items_number=Count('item__question'))

This one is the closest result that I got:

{'item__question': 429, 'items_number': 1}
{'item__question': 430, 'items_number': 2}
{'item__question': 431, 'items_number': 1}

But I have not the item_ids 762,763...

Thank you for reading

Answer 1

You can work with the ArrayAgg aggregate [Django-doc] to obtain a list of items:

from django.contrib.postgres.aggregates import ArrayAgg

QuizzUserItem.objects.filter(
    examuser=user_exam
).values(
    'item__question'
).annotate(
    items=ArrayAgg('item__question')
).order_by('item__question')