java - ManyToMany Hibernate保存相关对象

Question

我正在学习 Spring JPA，我从将对象映射到表开始。我对 OneToOne 和 OneToMany 关系没有任何问题，但我不太明白为什么我无法保留与 ManyToMany 关系相关的对象。我有一本可以有很多作者的书和一个可以有很多书的作者。模式是使用中间表 book_author 直接生成的(我可以在 MySql Workbench 中看到它)，但我得到了这个异常(exception):

Hibernate:插入作者(名字，姓氏)值(？，？)

Hibernate:插入书籍(种类，标题)值(？，？)

Hibernate:插入书籍(种类，标题)值(？，？)

Hibernate:插入author_book(author_id，book_id)值(？，？)

Hibernate:插入author_book(author_id，book_id)值(？，？)

Hibernate:插入作者(名字，姓氏)值(？，？)

线程“main”中的异常org.springframework.dao.InvalidDataAccessApiUsageException:传递给持久化的分离实体:com.example.demo.models.Book；嵌套异常是 org.hibernate.PersistentObjectException:传递给持久化的分离实体:com.example.demo.models.Book

我还粘贴了 Hibernate 操作，效果很好。

这些是我的实体定义:

@Table(name = "author")
public class Author {

    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    private Long id;
    private String firstName;
    private String lastName;

    @ManyToMany(cascade = {CascadeType.PERSIST, CascadeType.ALL})
    @JoinTable(
            name = "author_book",
            joinColumns = {@JoinColumn(name = "author_id")},
            inverseJoinColumns = {@JoinColumn(name = "book_id")}
            )
    private List<Book> books = new ArrayList<Book>();

    //getters and setters omitted for brevity
}

@Entity(name = "Book")
@Table(name = "book")
public class Book {

    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    private Long id;
    private String title;
    private String kind;
    @ManyToMany(mappedBy = "books")
    private List<Author> authors = new ArrayList<Author>();

    //getters and setters omitted for brevity
}

这些是我的存储库:

@Repository
public interface AuthorRepository extends CrudRepository<Author, Long> {

}

@Repository
public interface BookRepository extends CrudRepository<Book, Long> {

}

最后这是我的主要内容

public static void main(String[] args) {
        ApplicationContext ctx = SpringApplication.run(DemoApplication.class, args);
        AuthorRepository authorRepository = ctx.getBean(AuthorRepository.class);
        BookRepository bookRepository = ctx.getBean(BookRepository.class);

        Author author = new Author();
        author.setFirstName("Author");
        author.setLastName("First");

        Author author2 = new Author();
        author.setFirstName("Author");
        author.setLastName("Second");

        Book book1 = new Book();
        book1.setTitle("Book 1");
        book1.setKind("History");
        book1.getAuthors().add(author);
        book1.getAuthors().add(author2);

        Book book2 = new Book();
        book2.setTitle("Book 2");
        book2.setKind("Science");
        book2.getAuthors().add(author);

        author.getBooks().add(book1);
        author.getBooks().add(book2);
        author2.getBooks().add(book1);

        authorRepository.save(author);
        authorRepository.save(author2);

        System.out.println("-->End of db operation");

    }

Answer 1

在 Author 类中创建一个新方法来添加 book，而不是使用 author.getBooks().add(book1)

    public void addBook(Book book) {
        books.add(book);
        books.authors.add(this);
    }

而且您也不应该使用CascadeType.ALL，因为删除实体时关系的另一端也会被删除