Count objects in queryset by value in a field. Django - django

Question

Imagine I have a model which looks something like following:
class Car(models.Model):
TYPE_CHOICES = [
(1: 'Hatchback')
(2: 'Saloon')
type = models.CharField(choices=TYPE_CHOICES, ...)
color = models.CharField()
owner = models.ForeignKey(User, ...)
And I want to count objects by specific values. Say black saloons owned by Johns or white hatchbacks owned by Matts.
The best what I came up so far is:
Car.objects.annotate(
black_saloons_owned_by_Johns=Count(
'type',
filter=(
Q(type=2) &
Q(owner__first_name='John')
)
),
white_hatchbacks_owned_by_Matts=Count(
'type',
filter=(
Q(type=1) &
Q(owner__first_name='Matt')
)
)
).aggregate(
aggregated_black_saloons_owned_by_Johns=Sum(
'black_saloons_owned_by_Johns'
),
aggregated_white_hatchbacks_owned_by_Matts=Sum(
'white_hatchbacks_owned_by_Matts'
)
)
Is there a better way to get the desired result? Thanks.
Update.
As I said, I need to perform multiple lookups in a single query. The query I used had just one example. I updated it. Should have explicitly point it out. Sorry.

Answer 1

We can filter the queryset, and then use .count() [Django-doc]:
Car.objects.filter(type=2, owner__first_name='John').count()
or if you need to perform multiple lookups, you can use .aggregate(..) directly:
You can Count the Car objects directly with:
Car.objects.aggregate(
total_john=Count(
'pk', filter=Q(type=2, owner__first_name='John')
),
total_matts=Count(
'pk', filter=Q(type=1, owner__first_name='Matt')
)
)
this will then return a dictionary that has two keys: 'total_john' and 'total_matts', and these will contain the count of their number of Cars respectively.