Hibernate NonUniqueObjectException多对多

Question

我已经建立了多对多关系：

@Entity
@Table(name = "Orders")
public class Order {

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

@ManyToOne
@JoinColumn(name = "UserId")
private User user;

@ManyToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
@JoinTable(name = "order_products", joinColumns = {@JoinColumn(name = "Order_id")},
        inverseJoinColumns = {@JoinColumn(name = "Product_id")})
private List<Product> products;

产品：

@Entity
@Table(name = "products")
public class Product {

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


@NotNull
@Size(min = 5, max = 30)
@Column(name = "Name")
private String name;


@NotNull
@Column(name = "Price")
private double price;

@ManyToMany(fetch = FetchType.EAGER, mappedBy = "products")
private List<Order> orders;

和sql代码；

CREATE TABLE IF NOT EXISTS products (
  Id    INT PRIMARY KEY AUTO_INCREMENT,
  Name  VARCHAR(30) UNIQUE NOT NULL,
  Price DOUBLE             NOT NULL
);
CREATE TABLE IF NOT EXISTS orders (
  Id     INT PRIMARY KEY AUTO_INCREMENT,
  UserId INT,
  FOREIGN KEY (UserId) REFERENCES users (Id)
);
CREATE TABLE IF NOT EXISTS order_products (
  Order_id   INT,
  Product_id INT,
  FOREIGN KEY (Order_id) REFERENCES orders (Id),
  FOREIGN KEY (Product_id) REFERENCES products (Id)
)

当我插入具有所有不同产品的订单时，所有产品都可以使用，但是当我要在一个订单中添加两个相同产品时，执行代码时出现错误：

Session session = sessionFactory.openSession();
try {
    session.beginTransaction();
    session.save(order);
    session.getTransaction().commit();
    session.close();
} catch (RuntimeException e) {
    session.getTransaction().rollback();
    session.close();
    e.printStackTrace();
}

错误：

org.hibernate.NonUniqueObjectException：具有相同标识符值的另一个对象已与会话相关联：[org.training.ytaranau.model.Product＃1]

可能是什么原因？

Answer 1

请检查您提供或插入到产品实体的uniq ID。 它是产品的相同ID。

Answer 2

如前所述，您通过两次添加相同的对象来制动关系的唯一性。

因此，作为解决方案，您可以制作一个关联对象（如ProductOrder）并添加一个数量字段。

@Entity
public class ProductOrder {
    @Id
    private long orderId;

    @Id
    private long productId;

    private int quantity;

    @ManyToOne
    @PrimaryKeyJoinColumn(name="ORDERID", referencedColumnName="ID")
    private Order order;

    @ManyToOne
    @PrimaryKeyJoinColumn(name="PRODUCTID", referencedColumnName="ID")
    private Product product;
}

Order {
    @OneToMany(mappedBy="order")
    private List<ProductOrder> prodctOrder;
}

Product {
    @OneToMany(mappedBy="product")
    private List<ProductOrder> prodctOrder;
}