I have a customer table and customer order table as below
class Customer(models.Model):
name = models.CharField()
class CustomerOder(models.Model):
customer = models.ForiengKey(Customer)
item = models.CharField()
datetime_of_purchase = models.DateField()
Sample database entry
Table: Customer
id name
1 A
2 B
3 C
Table: CustomerOrder
id customer item datetime_of_purchase
1 A item_3 2021-11-10 10:00:00
2 A item_2 2021-11-11 10:00:00
3 B item_1 2021-11-11 10:00:00
4 A item_1 2021-11-12 10:00:00
5 B item_2 2021-11-12 10:00:00
6 C item_1 2021-11-13 10:00:00
Suppose i need to filter customer whose latest purchase is 'items_1' so the sample after filtering should get only Customer 'A' and 'C' whose latest purchase is 'item_1'
Sample:
<QuerySet [<Customer: A>, <Customer: C>]>
You can obtain the latest pruchased item with a Subquery expression [Django-doc]:
from django.db.models import OuterRef, Subquery
Customer.objects.alias(
latest_purchase=Subquery(
CustomerOrder.objects.filter(
customer_id=OuterRef('pk')
).order_by('-datetime_of_purchase').values('item')[:1]
)
).filter(latest_purchase='item_1')Prior to django-3.2, one uses .annotate(…) [Django-doc] over .alias(…) [Django-doc]:
from django.db.models import OuterRef, Subquery
Customer.objects.annotate(
latest_purchase=Subquery(
CustomerOrder.objects.filter(
customer_id=OuterRef('pk')
).order_by('-datetime_of_purchase').values('item')[:1]
)
).filter(latest_purchase='item_1')