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Changes between Initial Version and Version 1 of Ticket #13839, comment 18

initial	v1
3	3	> 1. The point of selected_related() is that it avoids doing an extra lookup. With the proposed fix, when the related object does not exist, accessing the attribute will cause the lookup to happen. This throws the `DoesNotExist` as it ought to, but the lookup shouldn't happen at all. I imagine that one way to fix this, while preserving the efficiency of select_related, is to use some other sentinel value that triggers a `DoesNotExist` exception inside the OneToOne descriptor. (Since querysets need to be pickled, remember that the simplest choice of sentinel value is a class).
4	4
5		Added test for this. A second sentinel is not needed, because we can just check the field.null if None is a valid value.
	5	Added test for this. A second sentinel is not needed, because we can just check the field.null if None is a valid value (Edit: currently, this is always False so we can just raise the exception on None, see below).
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