Bidirectional one-to-one relations with multiple join columns break in DQL queries

[Ma27]

Bug Report

Q	A
BC Break	yes
Version	2.6.3 (introduced in 2.6.0)

Summary

DQL queries including bidirectional one-to-one relations break with an exception as BasicEntityPersister#loadOneToOne assumes that such relations consist of a single join column since a360da5 as ClassMetadataInfo#getFieldForColumn breaks if an association mapping has more than one column.

Current behavior

Queries as shown in my failing testcase fail with the following exception on 2.6:

Doctrine\ORM\Mapping\MappingException: Cannot find a field on 'Doctrine\Tests\Functional\OneToOneReference' that is mapped to column 'objectId'. Either the field does not exist or an association exists but it has multiple join columns.

/home/ma27/Projects/orm/lib/Doctrine/ORM/Mapping/MappingException.php:621
/home/ma27/Projects/orm/lib/Doctrine/ORM/Mapping/ClassMetadataInfo.php:2961
/home/ma27/Projects/orm/lib/Doctrine/ORM/Persisters/Entity/BasicEntityPersister.php:805
/home/ma27/Projects/orm/lib/Doctrine/ORM/UnitOfWork.php:2708
/home/ma27/Projects/orm/lib/Doctrine/ORM/Internal/Hydration/ObjectHydrator.php:271
/home/ma27/Projects/orm/lib/Doctrine/ORM/Internal/Hydration/ObjectHydrator.php:492
/home/ma27/Projects/orm/lib/Doctrine/ORM/Internal/Hydration/ObjectHydrator.php:162
/home/ma27/Projects/orm/lib/Doctrine/ORM/Internal/Hydration/AbstractHydrator.php:152
/home/ma27/Projects/orm/lib/Doctrine/ORM/AbstractQuery.php:976
/home/ma27/Projects/orm/lib/Doctrine/ORM/AbstractQuery.php:922
/home/ma27/Projects/orm/lib/Doctrine/ORM/AbstractQuery.php:726
/home/ma27/Projects/orm/tests/Doctrine/Tests/ORM/Functional/OneToOneWithMultipleJoinColumnsTest.php:43

How to reproduce

I created a failing testcase in my fork which passes on 2.5, but fails on 2.6.

I didn't test it on master as it misses the method Doctrine\ORM\Persisters\Entity\BasicEntityPersister#loadOneToOneEntity. I assume that 3.0/master is too far diverged from 2.6, so a reproduction on master will be way harder.

Expected behavior

That the $qb->getQuery()->getResult() (see my example) resolves to an entity and doesn't break with an exception.