fix(knex): hydrate nullable relations with joined strategy

Related: #4675

packages/knex/src/AbstractSqlDriver.ts

@@ -249,11 +249,14 @@ export abstract class AbstractSqlDriver<Connection extends AbstractSqlConnection
       }));
 
       if (!hasPK) {
-        // initialize empty collections
         if ([ReferenceType.MANY_TO_MANY, ReferenceType.ONE_TO_MANY].includes(relation.reference)) {
           result[relation.name] = result[relation.name] || [] as unknown as T[keyof T & string];
         }
 
+        if ([ReferenceType.MANY_TO_ONE, ReferenceType.ONE_TO_ONE].includes(relation.reference)) {
+          result[relation.name] = null;
+        }
+
         return;
       }
 

tests/issues/GH4675.test.ts

@@ -0,0 +1,114 @@
+import {
+  Entity,
+  LoadStrategy,
+  ManyToOne,
+  OneToOne,
+  OptionalProps,
+  PrimaryKey,
+  Property,
+  Ref,
+  Unique,
+} from '@mikro-orm/core';
+import { MikroORM } from '@mikro-orm/sqlite';
+
+@Entity()
+export class User {
+
+  @PrimaryKey()
+  id!: number;
+
+  @Property()
+  @Unique()
+  username!: string;
+
+  @OneToOne({ entity: () => Profile, mappedBy: (profile: Profile) => profile.user, nullable: true })
+  profile!: Ref<Profile> | null;
+
+  [OptionalProps]?: 'profile';
+
+}
+
+@Entity()
+export class Profile {
+
+  @PrimaryKey()
+  id!: number;
+
+  @OneToOne({ entity: () => User, inversedBy: user => user.profile, owner: true, hidden: true })
+  user!: User;
+
+  @Property()
+  name!: string;
+
+}
+
+@Entity()
+export class Session {
+
+  @PrimaryKey()
+  id!: number;
+
+  @Property()
+  token!: string;
+
+  @ManyToOne({ entity: () => User })
+  user!: User;
+
+}
+
+let orm: MikroORM;
+
+test('GH #4675', async () => {
+  orm = await MikroORM.init({
+    entities: [Session],
+    dbName: ':memory:',
+  });
+  await orm.schema.createSchema();
+
+  const user = await orm.em.insert(User, { username: 'username' });
+  await orm.em.insert(Session, { token: 'abc123', user });
+
+  const session1 = await orm.em.findOneOrFail(Session, { token: 'abc123' }, {
+    populate: ['user', 'user.profile'],
+    strategy: LoadStrategy.SELECT_IN,
+    disableIdentityMap: true,
+  });
+  expect(session1.user.profile).toBeNull();
+
+  const session2 = await orm.em.findOneOrFail(Session, { token: 'abc123' }, {
+    populate: ['user', 'user.profile'],
+    strategy: LoadStrategy.JOINED,
+    disableIdentityMap: true,
+  });
+  expect(session2.user.profile).toBeNull();
+
+  await orm.close();
+});
+
+test('GH #4675 (forceUndefined: true)', async () => {
+  orm = await MikroORM.init({
+    entities: [Session],
+    dbName: ':memory:',
+    forceUndefined: true,
+  });
+  await orm.schema.createSchema();
+
+  const user = await orm.em.insert(User, { username: 'username' });
+  await orm.em.insert(Session, { token: 'abc123', user });
+
+  const session1 = await orm.em.findOneOrFail(Session, { token: 'abc123' }, {
+    populate: ['user', 'user.profile'],
+    strategy: LoadStrategy.SELECT_IN,
+    disableIdentityMap: true,
+  });
+  expect(session1.user.profile).toBeUndefined();
+
+  const session2 = await orm.em.findOneOrFail(Session, { token: 'abc123' }, {
+    populate: ['user', 'user.profile'],
+    strategy: LoadStrategy.JOINED,
+    disableIdentityMap: true,
+  });
+  expect(session2.user.profile).toBeUndefined();
+
+  await orm.close();
+});