這里是db模式

CREATE TABLE Products

(

id INT NOT NULL AUTO_INCREMENT,

category_id INT NOT NULL,

description VARCHAR(100),

price DECIMAL(10, 2) NOT NULL,

PRIMARY KEY (id),

FOREIGN KEY (category_id) REFERENCES Categories(id)

) ENGINE = INNODB;

CREATE TABLE Orders

(

id INT NOT NULL AUTO_INCREMENT,

customer_id INT NOT NULL,

status VARCHAR(20) NOT NULL,

date_created TIMESTAMP DEFAULT CURRENT_TIMESTAMP,

PRIMARY KEY (id),

FOREIGN KEY (customer_id) REFERENCES Customers(id)

) ENGINE = INNODB;

CREATE TABLE OrderDetails

(

product_id INT NOT NULL,

order_id INT NOT NULL,

quantity INT NOT NULL,

subtotal DECIMAL(10, 2) NOT NULL,

PRIMARY KEY (product_id, order_id),

FOREIGN KEY (product_id) REFERENCES Products(id),

FOREIGN KEY (order_id) REFERENCES Orders(id)

) ENGINE = INNODB;

模特

@Embeddable

public class OrderDetailPK

{

private Product product;

private Order order;

public OrderDetailPK() {}

public OrderDetailPK(Product product, Order order)

{

this.product = product;

this.order = order;

}

}

public class OrderDetail {

@EmbeddedId

private OrderDetailPK id;

@ManyToOne(cascade=CascadeType.ALL)

@JoinColumn(name="product_id", insertable=false, updatable=false)

private Product product;

@ManyToOne(cascade=CascadeType.ALL)

@JoinColumn(name="order_id", insertable=false, updatable=false)

private Order order;

private int quantity;

private double subtotal;

public OrderDetail() {}

public OrderDetail(OrderDetailPK id, int quantity, double subtotal)

{

this.product = id.getProduct();

this.order = id.getOrder();

this.quantity = quantity;

this.subtotal = subtotal;

}

// getters, setters

}

public class Product {

@Id

private int id;

private String description;

private double price;

@ManyToOne

@JoinColumn(name="category_id")

private Category category;

@OneToMany(cascade = CascadeType.ALL, mappedBy = "Products")

private List orderDetail;

}

public class Order {

@Id

private int id;

@ManyToOne

@JoinColumn(name="customer_id")

private Customer customer;

@OneToMany(cascade = CascadeType.ALL, mappedBy = "Orders")

private List orderDetail;

}

由于某些原因,我不斷收到錯誤

Concrete type "class models.OrderDetail" with application identity does not declare any primary key fields.

誰能指出我問題出在哪里？謝謝

最佳答案 當我之前這樣做時(詳見

this question and answer),我在可嵌入的ID原語中創建了字段(對應于所引用實體的ID字段),然后在實體中使用了

@MapsId.我相信這是滿足所有要求的最簡單(并且我敢說是正確的)：實體中的字段是關系,ID類中的字段是原始的,每列都只映射一次(@MapsId字段不是真正的映射,而是一些別名).

將其應用于您的案例,ID類如下所示：

@Embeddable

public class OrderDetailPK {

private final int productId;

private final int orderId;

public OrderDetailPK(int productId, int orderId) {

this.productId = productId;

this.orderId = orderId;

}

}

實體類看起來像：

public class OrderDetail {

@EmbeddedId

private OrderDetailPK id;

@ManyToOne(cascade = CascadeType.ALL)

@MapsId("productId")

private Product product;

@ManyToOne(cascade = CascadeType.ALL)

@MapsId("orderId")

private Order order;

private int quantity;

private double subtotal;

public OrderDetail(Product product, Order order, int quantity, double subtotal) {

this.id = new OrderDetailPK(product.getId(), order.getId());

this.product = product;

this.order = order;

this.quantity = quantity;

this.subtotal = subtotal;

}

protected OrderDetail() {}

}

總結

以上是生活随笔為你收集整理的java实现多对多关系的方法_java – 如何在JPA中实现复杂的多对多关系？的全部內容，希望文章能夠幫你解決所遇到的問題。

如果覺得生活随笔網站內容還不錯，歡迎將生活随笔推薦給好友。