feat(core): allow adding items to not initialized collections (#489)

tests/EntityManager.mysql.test.ts

@@ -1908,6 +1908,56 @@ describe('EntityManagerMySql', () => {
     expect(() => orm.em.remove(Book2, null)).toThrowError(`You cannot call 'EntityManager.remove()' with empty 'where' parameter. If you want to remove all entities, use 'em.remove(Book2, {})'.`);
   });
 
+  test('adding items to not initialized collection', async () => {
+    const god = new Author2('God', 'hello@heaven.god');
+    const b1 = new Book2('Bible 1', god);
+    await orm.em.persistAndFlush(b1);
+    orm.em.clear();
+
+    const a = await orm.em.findOneOrFail(Author2, god.id);
+    expect(a.books.isInitialized()).toBe(false);
+    const b2 = new Book2('Bible 2', a);
+    const b3 = new Book2('Bible 3', a);
+    a.books.add(b2, b3);
+    await orm.em.flush();
+    orm.em.clear();
+
+    const a2 = await orm.em.findOneOrFail(Author2, god.id, ['books']);
+    expect(a2.books.count()).toBe(3);
+    expect(a2.books.getIdentifiers()).toEqual([b1.uuid, b2.uuid, b3.uuid]);
+
+    const tag1 = new BookTag2('silly');
+    const tag2 = new BookTag2('funny');
+    const tag3 = new BookTag2('sick');
+    const tag4 = new BookTag2('strange');
+    let tag5 = new BookTag2('sexy');
+    a2.books[0].tags.add(tag1);
+    a2.books[1].tags.add(tag1);
+    a2.books[2].tags.add(tag5);
+    await orm.em.flush();
+    orm.em.clear();
+
+    const a3 = await orm.em.findOneOrFail(Author2, god.id, ['books']);
+    tag5 = orm.em.getReference(BookTag2, tag5.id);
+    a3.books[0].tags.add(tag3);
+    a3.books[1].tags.add(tag2, tag5);
+    a3.books[2].tags.add(tag4);
+    await orm.em.flush();
+    orm.em.clear();
+
+    const a4 = await orm.em.findOneOrFail(Author2, god.id, ['books.tags']);
+    expect(a4.books[0].tags.getIdentifiers()).toEqual([tag1.id, tag3.id]);
+    expect(a4.books[1].tags.getIdentifiers()).toEqual([tag1.id, tag2.id, tag5.id]);
+    expect(a4.books[2].tags.getIdentifiers()).toEqual([tag5.id, tag4.id]);
+    orm.em.clear();
+
+    const tag = await orm.em.findOneOrFail(BookTag2, tag1.id);
+    const book = await orm.em.findOneOrFail(Book2, b3.uuid);
+    tag.books.add(book);
+    await orm.em.flush();
+    orm.em.clear();
+  });
+
   afterAll(async () => orm.close(true));
 
 });