fix(core): fix hydration of 1:1 FK as PK property via joined strategy

Closes #4160

packages/core/src/entity/EntityHelper.ts

@@ -198,7 +198,7 @@ export class EntityHelper {
     helper(entity).__pk = helper(entity).getPrimaryKey()!;
 
     // the inverse side will be changed on the `value` too, so we need to clean-up and schedule orphan removal there too
-    if (value?.[prop2.name as string] != null && value?.[prop2.name as string] !== entity) {
+    if (!prop.primary && value?.[prop2.name as string] != null && Reference.unwrapReference(value?.[prop2.name as string]) !== entity) {
       const other = Reference.unwrapReference(value![prop2.name as string]);
       delete helper(other).__data[prop.name];
 

tests/issues/GH4160.test.ts

@@ -0,0 +1,94 @@
+import { Collection, Entity, LoadStrategy, ManyToOne, OneToMany, OneToOne, OptionalProps, PrimaryKey, Property, Rel } from '@mikro-orm/core';
+import { MikroORM } from '@mikro-orm/better-sqlite';
+
+@Entity()
+class Account {
+
+  [OptionalProps]?: 'client';
+
+  @PrimaryKey()
+  id!: string;
+
+  @Property()
+  name!: string;
+
+  @OneToOne(() => Client, c => c.account)
+  client!: Rel<Client>;
+
+}
+
+@Entity()
+class Client {
+
+  @OneToOne({ primary: true, entity: () => Account })
+  account!: Account;
+
+  @OneToMany(() => Brand, brand => brand.client, { orphanRemoval: true })
+  brands = new Collection<Brand>(this);
+
+}
+
+@Entity()
+class Brand {
+
+  @PrimaryKey()
+  id!: string;
+
+  @ManyToOne(() => Client)
+  client!: Client;
+
+}
+
+let orm: MikroORM;
+
+beforeAll(async () => {
+  orm = await MikroORM.init({
+    entities: [Client, Account, Brand],
+    dbName: ':memory:',
+  });
+  await orm.schema.refreshDatabase();
+
+  const account1 = orm.em.create(Account, { name: 'Account 1', id: '1' });
+  const client1 = orm.em.create(Client, { account: account1 });
+  orm.em.create(Brand, { id: '1', client: client1 });
+  orm.em.create(Brand, { id: '2', client: client1 });
+  await orm.em.flush();
+});
+
+beforeEach(async () => {
+  orm.em.clear();
+});
+
+afterAll(async () => {
+  await orm.close(true);
+});
+
+it('populate with select-in strategy', async () => {
+  const brands1 = await orm.em.find(Brand, {}, {
+    populate: ['client.account'],
+    strategy: LoadStrategy.SELECT_IN,
+  });
+
+  expect(brands1[0].client.account).toMatchObject({ id: '1', name: 'Account 1' });
+  expect(brands1[1].client.account).toMatchObject({ id: '1', name: 'Account 1' });
+});
+
+it('populate with joined strategy', async () => {
+  const brands1 = await orm.em.find(Brand, {}, {
+    populate: ['client.account'],
+    strategy: LoadStrategy.JOINED,
+  });
+
+  expect(brands1[0].client.account).toMatchObject({ id: '1', name: 'Account 1' });
+  expect(brands1[1].client.account).toMatchObject({ id: '1', name: 'Account 1' });
+});
+
+it('populate with query builder', async () => {
+  const brands2 = await orm.em
+    .createQueryBuilder(Brand, 'brand')
+    .leftJoinAndSelect('brand.client', 'client')
+    .leftJoinAndSelect('client.account', 'account');
+
+  expect(brands2[0].client.account).toMatchObject({ id: '1', name: 'Account 1' });
+  expect(brands2[1].client.account).toMatchObject({ id: '1', name: 'Account 1' });
+});