fix(database): prevent deeply nested has many map adding extra empty object

[nunntom]

closes #1994

• Added failing assertion to existing test showing the bug
• Removed line in SelectModelMapper that adds initial empty model. It doesn't seem necessary since the later $data->set adds the full nested path anyway. Please correct me if I'm wrong or if I broke anything. Tests are all still passing (including the failing one I added).

[github-actions]

Benchmark Results

Comparison of deeply-nested-has-many-map-bug against 3.x (5563eac1332581f39b908f0e4b23adf53167c282).

Open to see the benchmark results

Benchmark	Set	Mem. Peak	Time	Variability
ViewRenderBench(benchPlainHtml)	-	21.481mb 0.00%	488.857μs -5.87%	±3.67% +27.95%

_{Generated by phpbench against commit 7c8dee2}

[brendt]

Ping me when ready for review :)

[nunntom]

Yes please, ready for review @brendt

[brendt]

I wonder if we might have missed a test for this piece of code originally, because I'm kind of skeptical about removing it and everything just… continuing to work. Or, it could also be a leftover from an old iteration. I honestly don't remember.

So I'm going to merge this, and we'll see if something goes wrong :)

[nunntom]

Yeah, I don't get what that piece of code could have originally been for. My reasoning is doesn't the later $data->set recursively add any needed unset parents when adding a new child? Which would make it unnecessary to preemptively add the empty parent.

If it's any comfort I've been running a composer-patch of this change for a few weeks and haven't seen any issues, though I'm probably not covering anywhere near all use-cases. Fingers crossed!

Thanks for merging! :)

[brendt]

I had Claude take a look at it for 10 minutes because I genuinely didn't know anymore.

I now think it was added to deal with setting an empty array for the first iteration so that the array itself was present. However, we're now using $data->set($key, $value); which also does these "initialize missing nested array checks" for us, so the buggy part wasn't needed anymore.

At least, that's my understanding for now. We'll see how it goes :)