Django - Can you use property as the field in an aggregation function?

Question

I know the short answer because I tried it. Is there any way to accomplish this though (even if only on account of a hack)?

class Ticket(models.Model):
    account = modelfields.AccountField()
    uuid = models.CharField(max_length=36, unique=True)
    created = models.DateTimeField(auto_now_add=True)

    class Meta:
        ordering = ['created']

    @property
    def repair_cost(self):
        # cost is a @property of LineItem(models.Model)
        return self.lineitem_set.aggregate(models.Sum('cost'))

You really need to show the LineItem model also. – Jason Christa Jun 18 '10 at 00:31 — Jason Christa, Jun 18 '10 at 00:31

score 29 · Accepted Answer · answered Jun 18 '10 at 00:59

29

No. Anything that goes through a built-in manager has to be a real field, since they only touch the database. In order to work with a property they'd have to turn every record in the table into a model, then filter through them in Python.

answered Jun 18 '10 at 00:59

Ignacio Vazquez-Abrams

776,304
153
1,341
1,358

thanks. I thought that might be the case. I pictured `get all lineitemss and then call their cost property` but that would be so expensive :( – orokusaki Jun 18 '10 at 14:56

score 5 · Answer 2 · answered Jun 20 '16 at 07:17

5

I have a similar scenario and want exactly the same feature. I solved it trivially with the following line:

...
return sum(lt.cost for lt in self.lineitem_set)

answered Jun 20 '16 at 07:17

Fish Monitor

4,155
3
32
53

2

But it's slow, too slow, compared to django ORM – mr L Apr 12 '19 at 12:34
@abinax what would you suggest then? – ataraxis Dec 11 '20 at 01:18
This hits the database as a seperate query for every object in the queryset. – William Feb 12 '21 at 17:58

score 0 · Answer 3 · answered Jul 31 '22 at 04:48

0

can use django-queryable-properties

answered Jul 31 '22 at 04:48

hadi ahadi

116
1
1
6

1

While this link may answer the question, it is better to include the essential parts of the answer here and provide the link for reference. Link-only answers can become invalid if the linked page changes. – Tyler2P Jul 31 '22 at 08:45
While this link may answer the question, it is better to include the essential parts of the answer here and provide the link for reference. Link-only answers can become invalid if the linked page changes. - [From Review](/review/late-answers/32373781) – vimuth Aug 04 '22 at 08:32

Django - Can you use property as the field in an aggregation function?

3 Answers3

Linked