fix(core): fix removing entity that has an inverse relation with M:1 …

…`owner` property

Closes #4578

packages/core/src/unit-of-work/UnitOfWork.ts

@@ -438,7 +438,7 @@ export class UnitOfWork {
       }
 
       // there is a value, and it is still a self-reference (e.g. not replaced by user manually)
-      if (rel?.[inverse] && entity === Reference.unwrapReference(rel[inverse])) {
+      if (!Utils.isCollection(rel) && rel?.[inverse] && entity === Reference.unwrapReference(rel[inverse])) {
         delete helper(rel).__data[inverse];
       }
     }

tests/issues/GH4578.test.ts

@@ -0,0 +1,57 @@
+import { Collection, Entity, ManyToOne, OneToMany, PrimaryKey, SimpleLogger } from '@mikro-orm/core';
+import { MikroORM } from '@mikro-orm/sqlite';
+import { mockLogger } from '../helpers';
+
+@Entity()
+class User {
+
+  @PrimaryKey()
+  id!: number;
+
+  @OneToMany(() => Team, team => team.owner)
+  teams = new Collection<Team>(this);
+
+}
+
+@Entity()
+class Team {
+
+  @PrimaryKey()
+  id!: number;
+
+  @ManyToOne(() => User)
+  owner?: User;
+
+}
+
+
+let orm: MikroORM;
+
+beforeAll(async () => {
+  orm = await MikroORM.init({
+    entities: [Team],
+    dbName: ':memory:',
+    loggerFactory: options => new SimpleLogger(options),
+  });
+  await orm.schema.createSchema();
+});
+
+afterAll(async () => {
+  await orm.close(true);
+});
+
+test(`GH issue 4578`, async () => {
+  orm.em.create(User, {});
+  await orm.em.flush();
+  orm.em.clear();
+  const [u] = await orm.em.find(User, {});
+
+  const mock = mockLogger(orm);
+  await orm.em.removeAndFlush(u);
+
+  expect(mock.mock.calls).toEqual([
+    ['[query] begin'],
+    ['[query] delete from `user` where `id` in (1)'],
+    ['[query] commit'],
+  ]);
+});