我有Book桌子和Author桌子。他們的關(guān)系是many-to-many。我的目標(biāo)我希望能夠堅持新書。如果書籍的作者已經(jīng)存在于Author表中，我不想在Author表中保留相同的作者。如果作者在表中不存在Author，則作者數(shù)據(jù)將保留在Author表中。以下是我聲明實體和 serviceImplementation 以保存數(shù)據(jù)的方式：書@Entity(name = "book")public class Book {    @Id    @GeneratedValue(strategy = GenerationType.IDENTITY)    private Long id;    @Column(name = "title", nullable = false)    private String title;    @Column(name = "year", nullable = false)    private String year;    @ManyToMany(cascade = CascadeType.ALL)    @JoinTable(      name = "book_author",      joinColumns = @JoinColumn(name = "book_id", referencedColumnName = "id"),      inverseJoinColumns = @JoinColumn(name = "author_id", referencedColumnName = "id"))    @JsonManagedReference    private Set<Author> author;    @ManyToOne(cascade = CascadeType.ALL, fetch = FetchType.LAZY)    @JoinColumn(name = "category_id", referencedColumnName = "id", nullable = false)    @JsonIgnoreProperties({"hibernateLazyInitializer", "handler"})     private BookCategory category;}作者@Entity(name = "author")public class Author {    @Id    @GeneratedValue(strategy = GenerationType.IDENTITY)    private Long id;    @Column(name = "name", nullable = false)    private String name;    @Column(name = "address", nullable = false)    private String address;    @ManyToMany(mappedBy = "author", cascade = CascadeType.ALL, fetch = FetchType.LAZY)    @JsonBackReference    private Set<Book> book;}如果所有作者都存在于Author表中或表中根本不存在，則上面的代碼是有效的Author。如果其中一個存在而另一個不存在，它將根據(jù)CascadeType我在定義實體時使用的錯誤拋出錯誤。