问题 I have one-directional related entities: @Entity public class Book { private String isbn; } @Entity private class Recommentation { @ManyToOne(optional = false, fetch = FetchType.LAZY) @JoinColumn(name = "book_id", nullable = false) @OnDelete(action = OnDeleteAction.CASCADE) private Book book; } And the following test: @RunWith(SpringRunner.class) @DataJpaTest public class BookRepositoryTest { @Autowired private TestEntityManager testEntityManager; @Autowired private BookRepository