这里是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,我不断收到错误

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

谁能指出我问题出在哪里？谢谢

最佳答案 当我之前这样做时(详见

this question and answer),我在可嵌入的ID原语中创建了字段(对应于所引用实体的ID字段),然后在实体中使用了

@MapsId.我相信这是满足所有要求的最简单(并且我敢说是正确的)：实体中的字段是关系,ID类中的字段是原始的,每列都只映射一次(@MapsId字段不是真正的映射,而是一些别名).

将其应用于您的案例,ID类如下所示：

@Embeddable

public class OrderDetailPK {

private final int productId;

private final int orderId;

public OrderDetailPK(int productId, int orderId) {

this.productId = productId;

this.orderId = orderId;

}

}

实体类看起来像：

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() {}

}