EntityIdentityCollisionException in OneToOne Id column with inheritance

[janatjak]

Bug Report

Q	A
Version	3.*

Summary

Using entity (with inheritance) as ID (by OneToOne) throw EntityIdentityCollisionException

BusinessCase:
    id: int
    contract: Contract (bidirectional OneToOne)

Contract:
    id: BusinessCase (bidirectional OneToOne)

Attachment:
    id: int
    contract: Contract

$entityManager->find(Attachment::class, 1); // throw Exception

Current behavior

Doctrine\ORM\Exception\EntityIdentityCollisionException: While adding an entity of class Doctrine\Tests\Proxies\__CG__\Doctrine\Tests\ORM\Functional\Ticket\GH12428Contract with an ID hash of "1" to the identity map,
another object of class Doctrine\Tests\ORM\Functional\Ticket\GH12428Contract was already present for the same ID. This exception
is a safeguard against an internal inconsistency - IDs should uniquely map to
entity object instances. This problem may occur if:

- you use application-provided IDs and reuse ID values;
- database-provided IDs are reassigned after truncating the database without
clearing the EntityManager;
- you might have been using EntityManager#getReference() to create a reference
for a nonexistent ID that was subsequently (by the RDBMS) assigned to another
entity.

Expected behavior

Don't allow add entity to identity map twice.

How to reproduce

<?php

declare(strict_types=1);

namespace Doctrine\Tests\ORM\Functional\Ticket;

use Doctrine\ORM\Mapping as ORM;
use Doctrine\Tests\OrmFunctionalTestCase;
use PHPUnit\Framework\Attributes\Group;

/** @see https://github.com/doctrine/orm/issues/12428 */
#[Group('GH12428')]
class GH12428Test extends OrmFunctionalTestCase
{
    protected function setUp(): void
    {
        parent::setUp();

        $this->createSchemaForModels(
            GH12428BusinessCase::class,
            GH12428Contract::class,
            GH12428Attachment::class,
        );
    }

    public function testIssue(): void
    {
        $businessCase = new GH12428ABusinessCase();
        $attachment   = new GH12428Attachment($businessCase->contract);

        $this->_em->persist($businessCase);
        $this->_em->persist($attachment);
        $this->_em->flush();
        $this->_em->clear();

        $loadedAttachment = $this->_em->find(GH12428Attachment::class, $attachment->id);
        self::assertNotNull($loadedAttachment);
    }
}

#[ORM\Entity]
#[ORM\InheritanceType('SINGLE_TABLE')]
#[ORM\DiscriminatorMap([
    'A' => GH12428ABusinessCase::class,
])]
abstract class GH12428BusinessCase
{
    #[ORM\Id]
    #[ORM\Column]
    #[ORM\GeneratedValue]
    public int|null $id = null;

    #[ORM\OneToOne(mappedBy: 'id', cascade: ['persist'])]
    public GH12428Contract $contract;

    public function __construct()
    {
        $this->contract = new GH12428Contract($this);
    }
}

#[ORM\Entity]
class GH12428ABusinessCase extends GH12428BusinessCase
{
}

#[ORM\Entity]
class GH12428Attachment
{
    #[ORM\Id]
    #[ORM\Column]
    #[ORM\GeneratedValue]
    public int|null $id = null;

    public function __construct(
        #[ORM\ManyToOne]
        public GH12428Contract $contract,
    ) {
    }
}

#[ORM\Entity]
class GH12428Contract
{
    public function __construct(
        #[ORM\Id]
        #[ORM\OneToOne(inversedBy: 'contract')]
        #[ORM\JoinColumn(name: 'id')]
        public GH12428BusinessCase $id,
    ) {
    }
}

Test case: janatjak@0dae9be
Result: https://github.com/janatjak/orm/actions/runs/24121411601/job/70376040902