Reverse one to one related object populated from incorrect query columns

[Daniel Hillier]

Extracting data for the related object from a queryset with a self referential one to one field gets the wrong data (incorrect columns) from the query when using a select_related with the reverse field.

The incorrect columns are introduced by the sqlcompiler mistaking the reverse select_related path as a part of a multiple concrete model inheritance structure.

[Daniel Hillier]

The proposed fix tests for self-referential relationships and avoids the multiple concrete model inheritance path in those instances.

Test added and all other tests are passing.

​https://github.com/danifus/django/tree/ticket_27594

[Tim Graham]

I left comments for improvement on the PR. Please uncheck "Patch needs improvement" after updating. A single squashed commit is fine. Thanks!

[Daniel Hillier]

Thanks for the review!

I've simplified the way I fixed the bug and implemented your suggestions.

I think the heart of the bug was the definition of from_parent. A relationship between two models isn't from_parent if the two model classes are the same. I've updated how from_parent is defined to reflect that corner case.

Happy to incorporate any further changes you may have.

[Tim Graham <timograham@…>]

In 7da37699:

Fixed #27594 -- Fixed select_related() with reverse self-referential OneToOneField.

Fixed definition of klass_info['from_parent'] so that two models aren't
considered from a parent class if the model classes are the same.

[Tim Graham <timograham@…>]

In 4a9f9cc5:

Fixed #27594 -- Fixed select_related() with reverse self-referential OneToOneField.

Fix definition of klass_info['from_parent']. The relationship between
two models shouldn't be considered as being from a parent class if the
model classes are the same.

Thanks Tim for the review.

[Tim Graham <timograham@…>]

In 01b3dc22:

[1.8.x] Reverted "Fixed #27594 -- Fixed select_related() with reverse self-referential OneToOneField."

This reverts commit 4a9f9cc521f09c60f56024eb6688e30ab86b998f. It was
accidentally pushed to this branch.