V6. When populating a Many-to-Many relationship that uses STI, the ORM joins on the wrong column of the pivot table

[YanDjin]

Describe the bug
On the version 6, when populating a Many-to-Many relation that uses STI (i did not specify a strategy), the ORM joins on the wrong column of the pivot table.
I tried the same with a relation that does not use STI and it does not seem to have the same issue.

To Reproduce
Steps to reproduce the behavior:

• use an entity that has a Many-to-Many relationship with an entity that uses STI
• use a find on the entity that owns the relation
• specify the relation to be populated, without specifying a strategy
• when loading the relation, the ORM will join on the wrong column

https://github.com/YanDjin/mikro-orm/blob/bug/find-sti-relation/tests/issues/GH4423.test.ts
this link contains the test that replicates the issue.

Expected behavior
To join the populate request on the correct column of the pivot table

Versions

Dependency	Version
node	18.16.0
typescript	5.0.4
mikro-orm	6.0.0-dev.82
your-driver	postgres/sqlite

[B4nan]

This one is a bit more tricky, I guess I will try to do a bigger refactor to get rid of the weird loadFromPivotTable driver method and use em.populate instead.

[YanDjin]

I just happened to add a hotfix PR, if you have the time to check it out :)

[B4nan]

I managed to remove the weird parts from QB (together with this problematic qb.autoJoinPivotTable method), still have a few failing tests to deal with, but this new solution does not suffer from the problem you have in the PR.