java - Hibernate 向用户添加一本书

Question

我在用户和图书之间建立了多对多关系。现在，我想将现有书籍添加到 User_Books 中的现有用户，但每次执行时都会在 User 表中创建一个空的新用户。

       Configuration cfg = new Configuration();
       cfg.configure("hibernate.cfg.xml");
       SessionFactory factory = cfg.buildSessionFactory();
       Session session = factory.openSession();
       Transaction tx = session.beginTransaction();

        Books book = new Books();
        book.setBookshareId(bookshareId);

        User user1 = new User();
        user1.setUser_id(userID);

        user1.getBooks().add(book);
        session.save(user1);

       tx.commit();

用户:

@Entity
@Table(name="tblUser")
public class User implements Serializable{

@Id
@Column(name = "Id",unique = true,nullable = false)
@GeneratedValue(strategy=GenerationType.AUTO)
private int Id;

@Column(name = "email")
private String email;

@Column(name = "password")
private String password;

@ManyToMany(mappedBy="user")  
private List<Books> books = new ArrayList<Books>(); 

public void addBooks(Books book) {
    this.books.add(book);
}

书籍:

@ManyToMany
@JoinTable(name = "User_Books",
    joinColumns = { @JoinColumn(name = "Books_id")},
    inverseJoinColumns = { @JoinColumn(name = "User_id")})
private List<User> user = new ArrayList<User>();

 public void addUser(User user) {
        this.user.add(user);
    }

@穆罕默德·纳布利当我执行这个时，它找到了它们，但是当我查看 User_Books 时，我什么也没看到。

                  DEBUG Collections - Collection found: [entity.bookdetail.Books.user#946669], was: [entity.bookdetail.Books.user#946669] (uninitialized)
12:00:37 web.1 |  DEBUG Collections - Collection found: [entity.users.User.books#6], was: [entity.users.User.books#6] (uninitialized)
12:00:37 web.1 |  DEBUG AbstractFlushingEventListener - Flushed: 0 insertions, 0 updates, 0 deletions to 2 objects
12:00:37 web.1 |  DEBUG AbstractFlushingEventListener - Flushed: 0 (re)creations, 1 updates, 0 removals to 2 collections
12:00:37 web.1 |  DEBUG EntityPrinter - Listing entities:
12:00:37 web.1 |  DEBUG EntityPrinter - entity.bookdetail.Books{copyright=1998-01-01 00:00:00.0, images=0, author=J. K. Rowling, briefSynopsis=Second in ...
12:00:37 web.1 |  DEBUG EntityPrinter - entity.users.User{password=u1t1, books=<uninitialized>, Id=6, email=user1@test1.com}
12:00:37 web.1 |  DEBUG JdbcTransaction - committed JDBC Connection
12:00:37 web.1 |  DEBUG LogicalConnectionImpl - Releasing JDBC connection
12:00:37 web.1 |  DEBUG LogicalConnectionImpl - Released JDBC connection

Answer 1

我希望这会起作用，

您的数据库中有用户和书籍，不要使用 new 来创建用户，您必须直接从数据库中获取它。

将此行添加到您的用户类的 ManyToMany 注释

@ManyToMany(mappedBy="user",cascade = {CascadeType.ALL})  
private List<Books> books = new ArrayList<Books>();

试试这个:

Books book = (Books) session.get(Books.class, book_id);
     User user =  (User) session.get(User.class, user_id);
     List<Books> books=user.getBooks();
     books.add(book);
     user.setBooks(books);

    session.saveOrUpdate(user);