fix(core): fix extra updates when nullable embedded properties contai…

…n FK

Closes #4788

packages/core/src/utils/EntityComparator.ts

@@ -615,7 +615,7 @@ export class EntityComparator {
       return this.getGenericComparator(this.wrap(prop.name), cond);
     }
 
-    return `  if (!equals(last${this.wrap(prop.name)}, current${this.wrap(prop.name)})) diff${this.wrap(prop.name)} = current${this.wrap(prop.name)};`;
+    return this.getGenericComparator(this.wrap(prop.name), `!equals(last${this.wrap(prop.name)}, current${this.wrap(prop.name)})`);
   }
 
   private wrap(key: string): string {

tests/features/embeddables/GH4788.test.ts

@@ -0,0 +1,123 @@
+import {
+  Embeddable,
+  Embedded,
+  Entity,
+  EventArgs,
+  EventSubscriber,
+  ManyToOne,
+  PrimaryKey,
+  PrimaryKeyProp,
+  PrimaryKeyType,
+  Property,
+  Ref,
+} from '@mikro-orm/core';
+import { MikroORM } from '@mikro-orm/sqlite';
+
+@Embeddable()
+class A {
+
+  @Property({ nullable: true })
+  alpha!: number | null;
+
+  @ManyToOne(() => C, { ref: true })
+  c!: Ref<C>;
+
+}
+
+@Entity()
+class B {
+
+  @PrimaryKey()
+  id!: number;
+
+  @Embedded({ entity: () => A, object: false, nullable: true })
+  a!: A | null;
+
+}
+
+@Entity()
+class C {
+
+  [PrimaryKeyType]!: number;
+  [PrimaryKeyProp]!: 'node';
+  @OneToOne({ entity: () => D, primary: true, onDelete: 'cascade', onUpdateIntegrity: 'cascade' })
+  node!: Ref<D>;
+
+}
+
+@Entity()
+class D {
+
+  @PrimaryKey()
+  id!: number;
+
+}
+
+@Embeddable()
+class A2 {
+
+  @Property()
+  alpha!: number | null;
+
+  @ManyToOne(() => C2, { ref: true })
+  c2!: Ref<C2>;
+
+}
+
+@Entity()
+class B2 {
+
+  @PrimaryKey()
+  id!: number;
+
+  @Embedded({ entity: () => A2, object: false, nullable: true })
+  a2!: A2 | null;
+
+}
+
+@Entity()
+class C2 {
+
+  @PrimaryKey()
+  id!: number;
+
+}
+
+class FooBarSubscriber implements EventSubscriber {
+
+  async afterUpdate(args: EventArgs<any>): Promise<void> {
+    throw new Error('afterUpdate called but nothing changed');
+  }
+
+}
+
+let orm: MikroORM;
+
+beforeAll(async () => {
+  orm = await MikroORM.init({
+    entities: [A, B, C, D, A2, B2, C2],
+    dbName: ':memory:',
+    subscribers: [new FooBarSubscriber()],
+  });
+  await orm.schema.createSchema();
+});
+
+afterAll(() => orm.close(true));
+
+test('embedded with ManyToOne to foreign key as primary key entity', async () => {
+  orm.em.create(B, { a: null });
+  await orm.em.flush();
+  orm.em.clear();
+  await orm.em.getRepository(B).findAll();
+  await orm.em.flush(); // update query is created
+  orm.em.clear();
+});
+
+test('embedded with ManyToOne to entity', async () => {
+  orm.em.create(B2, { a2: null });
+  await orm.em.flush();
+  orm.em.clear();
+  await orm.em.getRepository(B2).findAll();
+  await orm.em.flush(); // no update query is created
+  orm.em.clear();
+});