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How can a do a "greatest-n-per-group" query in django?

Asked 2010-01-21T17:57:51.563
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(This is the django version of the thread at SQL join: selecting the last records in a one-to-many relationship)

Suppose I have a table of customers and a table of purchases. Each purchase belongs to one customer. I want to get a list of all customers along with their last purchase. Can it be done without raw SQL and without multiple database queries?

sql django join greatest-n-per-group
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You can't do this in one query in Django. You can get the customer with just the date of their most recent purchase like this:

from django.db.models import Max
customers = Customer.objects.annotate(Max('purchase__date'))

but you don't automatically get access to the actual purchase this way.

answered 2010-01-21T19:09:13.093

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