Query question

[Lee Hinde]

Given this model, I want to find all ProductSale objects that have expired and where the Person doesn't have a later (unexpired) purchase of the same product.

class ProductSale(models.Model):

    product = models.ForeignKey(Product)

    person = models.ForeignKey(Person)

...

    date_expires = models.DateField(blank=True, db_index=True)

    

The closest I've gotten is in the shell where I get a values_list of person and product for expired and unexpired and then compare the two lists. That leaves me with a list of tuples, that (due to the size of the list, I think) I can't use in a query.extra. 

Any suggestions would be appreciated.

(and sorry for the lame subject. I couldn't think of a way to be both succinct and informative.)

[Dheerendra Rathor]

You should use 'F' expression from django.db.models

So your expression would be like: 

ProductSale.objects.all().filter(date_expires__lt = now().date).exclude(date_purchased__gt = F('date_expires'))

Which roughly translates to  

SELECT * FROM productsale WHERE date_expires < CURRENT_DATE AND NOT (date_purchased > date_expires)

in mysql.