spring - 使用 @ManyToOne 关联时传递到持久错误的分离实体

Question

我有Book & Bookdetail类

当我尝试使用相同的BookDetail时我的两个信息Book使用 @ManyToOne 的对象，我正在得到

"detached entity passed to persist error".

我尝试了同样的 JpaRepository和CrudRepository 。但结果相同

请帮助我。提前致谢

主类

@SpringBootApplication
public class HelloJpaApplication implements CommandLineRunner{

    private static final Logger logger = LoggerFactory.getLogger(HelloJpaApplication.class);

    @Autowired
    private BookRepository bookRepository;

    public void run(String... arg0) throws Exception {

        Book book1=new Book();
        book1.setName("my thoughts");

        Book book2=new Book();
        book2.setName("your thoughts");

        Bookdetail detail=new Bookdetail();
        detail.setCategory("good books");

        book1.setBookdetail(detail);
        book2.setBookdetail(detail);

        bookRepository.save(book1); 
        bookRepository.save(book2); 
    }

    public static void main(String[] args) {
        SpringApplication.run(HelloJpaApplication.class, args);
    }
}

BookRepository接口(interface)

public interface BookRepository extends JpaRepository<Book,Integer>{

}

图书类(class)

@Entity
public class Book {

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    private int bookid;

    private String name;

    @ManyToOne(cascade = {CascadeType.PERSIST,CascadeType.MERGE})
    private Bookdetail bookdetail;

    public Book() {
    }

    public Book(String name) {
    this.name=name;
    }

    public int getBookid() {
        return bookid;
    }
    public void setBookid(int bookid) {
        this.bookid = bookid;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Bookdetail getBookdetail() {
        return bookdetail;
    }
    public void setBookdetail(Bookdetail bookdetail) {
        this.bookdetail = bookdetail;
    }

}

图书详细信息类

@Entity
@Table(name="bookdetail")
public class Bookdetail {

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    private int bookid;

    private String category;

    public Bookdetail() {
    }
    public Bookdetail(String category) {
        this.category=category;
    }

    public String getCategory() {
        return category;
    }
    public void setCategory(String category) {
        this.category = category;
    }

}

Answer 1

仅使用 BookdetailDetail=new Bookdetail(); 创建的每个对象都是一个独立的实体，这意味着他不在 hibernate session 中或没有标识符id .
并且您必须将持久、更新或删除的服务包装到事务中。

因此，首先您必须保存detail您的分离实体:bookdetailRepository.save(detail)以将其附加到 session 但是在您的情况下您已指定 cascade = {CascadeType.PERSIST,CascadeType.MERGE}

@ManyToOne(cascade = {CascadeType.PERSIST,CascadeType.MERGE})
private Bookdetail bookdetail; 

无需事先保存，工作将自动完成。

解决方案是用@Transactional注释方法run()

...
@Transactional
public void run(String... arg0)
    ...
    bookdetailRepository.save(detail)
    book1.setBookdetail(detail);
    ...