feat(core): do not map array types as Loaded when partially loaded

Closes #5123

packages/core/src/typings.ts

@@ -965,7 +965,7 @@ type LoadedLoadable<T, E extends object> =
     ? LoadedReference<E>
     : T extends ScalarReference<infer U>
       ? LoadedScalarReference<U>
-      : T extends Scalar | Scalar[]
+      : T extends Scalar | any[]
           ? T
           : E;
 

tests/features/partial-loading/GH5123.test.ts

@@ -0,0 +1,38 @@
+import { Entity, PrimaryKey, Property, JsonType } from '@mikro-orm/core';
+import { MikroORM } from '@mikro-orm/sqlite';
+
+@Entity()
+class A {
+
+  @PrimaryKey()
+  id!: number;
+
+  @Property({ type: JsonType })
+  array!: B[];
+
+}
+
+interface B {
+  test: string;
+}
+
+let orm: MikroORM;
+
+beforeAll(async () => {
+  orm = await MikroORM.init({
+    entities: [A],
+    dbName: ':memory:',
+  });
+  await orm.schema.createSchema();
+});
+
+test('GH #5123', async () => {
+  const a = orm.em.create(A, { array: [{ test: 'test' }] });
+  await orm.em.persistAndFlush(a);
+
+  const a1 = await orm.em.fork().findOneOrFail(A, 1);
+  const a2 = await orm.em.fork().findOneOrFail(A, 1, { fields: ['array'] });
+
+  expect(a1.array.filter(i => i)).toEqual([{ test: 'test' }]);
+  expect(a2.array.filter(i => i)).toEqual([{ test: 'test' }]);
+});