Cannot update a query once a slice has been taken

Question

I am trying to do this:

UserLog.objects.filter(user=user).filter(action=\'message\').filter(timestamp__lt=now)[0:5].update(read=True)

but I

Answer 1

As the error states, you cannot call update() on a QuerySet if you took out a slice.

The reason:

1. Taking a slice is equivalent to a LIMIT statement in SQL.
2. Issuing an update turns your query into an UPDATE statement.

What you are trying to do would be equivalent to

UPDATE ... WHERE ... LIMIT 5

which is not possible, at least not with standard SQL.