fix(core): improve propagation of changes to 1:1 relations

Related: #3614

packages/core/src/entity/EntityHelper.ts

@@ -185,6 +185,16 @@ export class EntityHelper {
   private static propagateOneToOne<T extends object, O extends object>(entity: T, owner: O, prop: EntityProperty<O>, prop2: EntityProperty<T>, value?: T[keyof T & string], old?: T): void {
     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) {
+      const other = Reference.unwrapReference(value![prop2.name as string]);
+      delete helper(other).__data[prop.name];
+
+      if (prop2.orphanRemoval) {
+        helper(other).__em?.getUnitOfWork().scheduleOrphanRemoval(other);
+      }
+    }
+
     if (value == null) {
       entity[prop2.name] = value as T[keyof T & string];
     } else if (prop2.mapToPk) {

tests/issues/GH3614.test.ts

@@ -121,3 +121,21 @@ test('change a 1:1 relation with a new entity and not delete the old one', async
   const oldOwner2 = await orm.em.fork().findOne(User, oldOwner.id);
   expect(oldOwner2).not.toBeNull();
 });
+
+test('change a 1:1 relation with a new entity and delete the old one', async () => {
+  const project = await createProject();
+  const oldOwner = project.owner!;
+  orm.em.create(User, { name: 'Johnny', project1: 1 });
+  expect(oldOwner.unwrap().project1).toBeUndefined();
+
+  const mock = mockLogger(orm, ['query']);
+  await orm.em.flush();
+  const queries = mock.mock.calls.map(q => q[0]);
+
+  expect(queries[1]).toMatch('delete from `user` where `id` in (?)');
+  expect(queries[2]).toMatch('insert into `user` (`name`, `project1_id`) values (?, ?)');
+
+  const oldOwner2 = await orm.em.fork().findOne(User, oldOwner.id);
+  expect(oldOwner2).toBeNull();
+});
+