Models._get_unique_checks() does not return grandparents' unique checks

[jku]

Consider the following models:

class Project(models.Model):
    title = models.CharField(max_length=255)
    internal_id = models.CharField(max_length=255, unique=True)

class SubProject(Project):
    # ... fields of SubProject ...
    pass

class SubSubProject(SubProject):
    # ... fields of SubSubProject ...
    pass

Following code works as expected (b.full_clean() throws a ValidationError):

a = SubProject( title = 'A', internal_id = 1 )
a.save()
b = SubProject( title = 'B', internal_id = 1 )
b.full_clean() # Throws ValidationError

Following code does not work as expected (b.full_clean() does not throw an exception, b.save() throws an IntegrityError):

a = SubSubProject( title = 'A', internal_id = 2 )
a.save()
b = SubSubProject( title = 'B', internal_id = 2 )
b.full_clean() # Does not throw any exception!
b.save() # Throws IntegrityError, of course!

[sswang]

fix for sub sub inheritance uniqueness

[sswang]

still needs fix for unique_togethers

[aron45]

opened pull request ​https://github.com/django/django/pull/3968

[Josh Smeaton]

I presume you didn't mean to close this case off, since you've linked a pull request.

[aron45]

I updated the pull request

[Simon Charette <charette.s@…>]

In 79f27f2b61aeac763ae048416ef8a97c2b639ae8:

Fixed #15321 -- Honored ancestors unique checks.

Thanks to Tim for the review.

[Simon Charette <charette.s@…>]

In fc49e736484892eaa516826d93660c7ab53a6c3e:

[1.8.x] Fixed #15321 -- Honored ancestors unique checks.

Thanks to Tim for the review.

Backport of 79f27f2b61aeac763ae048416ef8a97c2b639ae8 from master