fix(core): propagation with nullable 1:1 relation

[alisd23]

Fixes #3850

I'm not very familar with the code, so I'm not confident with the solution, but I think this is what is needed.

Tests added and related tests for #3614 also still pass

[B4nan]

Amazing, thank you! I just briefly checked the repros but didn't have time to actually look into it just yet. The change looks fine to me, so as long as the test suite is passing, we are good to merge.

[alisd23]

No worries - just give me a few hours so I can add more test cases as I'm not quite sure this is the right solution.

Let me know if you've had time to check whether you think it's right/wrong 👍

[codecov-commenter]

Codecov Report

Base: 99.80% // Head: 99.80% // Increases project coverage by +0.00% 🎉

Coverage data is based on head (8233a70) compared to base (fb996cc).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3851   +/-   ##
=======================================
  Coverage   99.80%   99.80%           
=======================================
  Files         214      214           
  Lines       13582    13586    +4     
  Branches     3166     3169    +3     
=======================================
+ Hits        13555    13559    +4     
  Misses         25       25           
  Partials        2        2           

Impacted Files	Coverage Δ
packages/core/src/unit-of-work/UnitOfWork.ts	100.00% <100.00%> (ø)

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[alisd23]

Added a few more test cases, so now we cover:

• Adding a new entity to the relation (either side)
• Swapping an entity on the relation (either side)
• Unlinking an entity - but not deleting either entity (either side)
• Deleting an entity - (either side)

All seems to work as expected - hopefully nothing broken downstream

[alisd23]

@B4nan All comments are addressed now. I'm happier with the latest solution as I think it's more specific and makes more sense in my head. There's a hell of a lot of tests which is good, so hopefully it's not broken anything related to 1-M or M-M relations.

Feel free to squash all commits into the first when merging - thanks!

[alisd23]

All looks good now on CI 👍

Any idea when we might be able to release the fix? This is blocking the upgrade on my project unfortunately

[B4nan]

every commit to master is published to NPM as dev version, so you can try it in few minutes

i will probably do a patch release on sunday