Change persistence ordering for OneToOne to allow making JoinColumns non-nullable

[rvanlaak]

closes #7006
closes #6499
closes #5538
closes #4230

The issue as discussed earlier in #7006, #6499, #5538 and #4230 makes it harder to encapsulate behavior inside domain objects, when following some basic principles of DDD aggregate roots. In other words, the aggregate should not leak it's child nor have a dependency on a em/repo for the child to get persisted.

To be clear on the workaround, setting the @JoinColumn to nullable solves this, as Doctrine does take care of setting the id on the object at a later moment.

In response to discussing a fix for #6499 we borrowed the test as @Frikkle proposed in #6533 and slightly adjusted it to demonstrate the issue on persisting cascading relationships.

Expected

The exception we should get on running the test, that would confirm that the persistence ordering is wrong:

Exception : [Doctrine\ORM\ORMException] The identifier id is missing for a query of Doctrine\Tests\ORM\Functional\Ticket\DDC6499A

Actual

There is pending discussion in #6533 on a proposed fix.

As the tests in this PR pass, that proves that the commit ordering works correctly.

[rvanlaak]

@greg0ire I've fixed failing cs tests of commit 251e1a6 in 9a3bc3c , can you reapprove running the workflows?

[greg0ire]

I'm confused: how can a PR that changes only the tests directory fix any bug?

[rvanlaak]

The point would be that the tests in this PR should prove that the long-standing issues related to persistence ordering have been fixed by other changes/commits in the meanwhile, but that is something we should verify with a code review.

I've also locally cherry-picked these tests on the 2.6 branch, and tests also pass over there.

[mpdude]

@rvanlaak do I understand correctly that this PR provides test cases to show other issues being fixed?

If yes, it should not be too difficult to get these tests merged, and tests are always a good thing.

Could you rebase this to 2.14.x?

[rvanlaak]

@mpdude yes it should. I see you also asked the other ticket creators (the ones mentioned on this PR description) to verify the situation, so let's also wait for their answer.

[mpdude]

I'd love to get your 👀 on #10547

[rvanlaak]

@mpdude did check the changes and specifically the test cases on your PR, and they look extremely promising in solving all these commit order issues 👏

[rvanlaak]

Feel free to also mark this PR as closed with your PR #10547