When two STI subclasses both declare a @OneToMany with the same property name but different target entities, MikroORM.init crashes:

TypeError: rootProp.fieldNames is not iterable
    at MetadataDiscovery.js:1339:49
    at MetadataDiscovery.initSingleTableInheritance (MetadataDiscovery.js:1311)

Looks like the inverse-side counterpart of #7598. The fix in #7599 added sameRelationTargetRoot() to skip the rename branch for narrowed owning-side overrides, but it bails out for anything that isn't MANY_TO_ONE or ONE_TO_ONE:

if (prop.kind !== ReferenceKind.MANY_TO_ONE && prop.kind !== ReferenceKind.ONE_TO_ONE) {
  return false;
}

So OneToMany falls through into the rename branch, hits initFieldName(rootProp, ...) which doesn't set fieldNames for inverse-side props, and then [...rootProp.fieldNames] blows up.

The targets in the repro aren't narrowing the same hierarchy either — they're entirely separate entities — so the rename branch shouldn't run for them at all.

Expected behavior

Discovery should succeed. OneToMany on STI siblings has no column to merge, so it should just inherit.

Reproduction

npm i @mikro-orm/core@7.0.13 @mikro-orm/postgresql@7.0.13 and run:

import { MikroORM, defineEntity } from '@mikro-orm/core';

const p = defineEntity.properties;

const Animal = defineEntity({
  name: 'Animal',
  abstract: true,
  discriminatorColumn: 'type',
  properties: {
    id: p.string().primary(),
    type: p.string(),
    name: p.string(),
  },
});

const DogToy = defineEntity({
  name: 'DogToy',
  properties: {
    id: p.string().primary(),
    name: p.string(),
    owner: () => p.manyToOne(Dog),
  },
});

const CatToy = defineEntity({
  name: 'CatToy',
  properties: {
    id: p.string().primary(),
    name: p.string(),
    owner: () => p.manyToOne(Cat),
  },
});

const Dog = defineEntity({
  name: 'Dog',
  extends: Animal,
  discriminatorValue: 'DOG',
  properties: {
    toys: () => p.oneToMany(DogToy).mappedBy('owner'),
  },
});

const Cat = defineEntity({
  name: 'Cat',
  extends: Animal,
  discriminatorValue: 'CAT',
  properties: {
    toys: () => p.oneToMany(CatToy).mappedBy('owner'),
  },
});

const { PostgreSqlDriver } = await import('@mikro-orm/postgresql');
await MikroORM.init({
  driver: PostgreSqlDriver,
  entities: [Animal, Dog, Cat, DogToy, CatToy],
  dbName: 'never_connects',
  connect: false,
});

What driver are you using?

@mikro-orm/postgresql

MikroORM version

7.0.13

Node.js version

24.15.0

Operating system

Windows 11

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