django-aggregate-if 0.3.1

Conditional aggregates for Django, just like the famous SumIf in Excel.

Django Aggregate If: Condition aggregates for Django

Aggregate-if adds conditional aggregates to Django.

Conditional aggregates can help you reduce the ammount of queries to obtain aggregated information, like statistics for example.

Imagine you have a model Offer like this one:

class Offer(models.Model):
    sponsor = models.ForeignKey(User)
    price = models.DecimalField(max_digits=9, decimal_places=2)
    status = models.CharField(max_length=30)
    expire_at = models.DateField(null=True, blank=True)
    created_at = models.DateTimeField(auto_now_add=True)
    updated_at = models.DateTimeField(auto_now=True)

    OPEN = "OPEN"
    REVOKED = "REVOKED"
    PAID = "PAID"

Let’s say you want to know:

1. How many offers exists in total;

2. How many of them are OPEN, REVOKED or PAID;

3. How much money was offered in total;

4. How much money is in OPEN, REVOKED and PAID offers;

To get these informations, you could query:

from django.db.models import Count, Sum

Offer.objects.count()
Offer.objects.filter(status=Offer.OPEN).aggregate(Count('pk'))
Offer.objects.filter(status=Offer.REVOKED).aggregate(Count('pk'))
Offer.objects.filter(status=Offer.PAID).aggregate(Count('pk'))
Offer.objects.aggregate(Sum('price'))
Offer.objects.filter(status=Offer.OPEN).aggregate(Sum('price'))
Offer.objects.filter(status=Offer.REVOKED).aggregate(Sum('price'))
Offer.objects.filter(status=Offer.PAID).aggregate(Sum('price'))

In this case, 8 queries were needed to retrieve the desired information.

With conditional aggregates you can get it all with only 1 query:

from django.db.models import Q
from aggregate_if import Count, Sum

Offer.objects.aggregate(
    Count('pk'),
    Count('pk', only=Q(status=Offer.OPEN)),
    Count('pk', only=Q(status=Offer.REVOKED)),
    Count('pk', only=Q(status=Offer.PAID)),
    Sum('price'),
    Sum('price', only=Q(status=Offer.OPEN)),
    Sum('price'), only=Q(status=Offer.REVOKED)),
    Sum('price'), Q(status=Offer.PAID)),
)

Installation

To install django-aggregate-if, simply:

$ pip install django-aggregate-if

Inspiration

There is a ticket 11305 that will (hopefully) implement this feature into Django 1.6.

Using Django 1.4, I still wanted to avoid creating custom queries for very simple conditional aggregations. So I’ve cherry picked those ideas and others from the internet and built this library.

This library uses the same API and tests proposed on ticket 11305, so when the new feature is available you can easily replace django-aggregate-if.

Limitations

Conditions involving joins with aliases are not supported yet. If you want to help adding this feature, you’re welcome to check the first issue.

License

The MIT License.