Map的JPA（休眠）映射。 我应该为java.util.Map映射使用哪些注释？

Question

表结构：

TABLE products (id (PK), name, price);

TABLE orders (id (PK), customer_id, user_id);

//product_quantity is quantity of product in particular order
TABLE products_to_orders (product_id, order_id, product_quantity
  PRIMARY KEY (product_id, order_id),
  FOREIGN KEY (product_id) REFERENCES products (id) ON DELETE CASCADE,
  FOREIGN KEY (order_id) REFERENCES orders (id) ON DELETE CASCADE
);

这是我的Order.java ：

@Entity
@Table(name = "orders")
public class Order extends BaseEntity {
...
//this map holds Products and their quantities in order;
        @ManyToMany(fetch = FetchType.EAGER)
        @JoinTable(
                name = "products_to_orders"
                ,joinColumns = @JoinColumn(name = "order_id")
                ,inverseJoinColumns = @JoinColumn(name = "product_id") //it seems that i don't need this line
        )
        @MapKeyJoinColumn(name = "product_id")
        @Column(name = "product_quantity")
        private Map<Product, Integer> productQuantityMap;
...

我使用这些注释的映射不起作用。 它给出了一个例外：

原因：org.hibernate.AnnotationException：使用@OneToMany或@ManyToMany定位未映射的类：com.malikov.shopsystem.model.Order.productQuantityMap [java.lang.Integer]

因此，我无法管理如何正确注释此地图。 非常感谢您的帮助！ 这是我在GitHub上的代表的链接https://github.com/malikov-yurii/online-shop-management-system.git

UPDATE。 有两种正确的解决方案（来自Neil和Maciej）：

  Variation 1:
    @ElementCollection(fetch = FetchType.EAGER)
    @JoinTable(
            name = "products_to_orders"
            ,joinColumns = @JoinColumn(name = "order_id")
    )
    @MapKeyJoinColumn(name = "product_id")
    @Column(name = "product_quantity")
    private Map<Product, Integer> productQuantityMap;

  Variation 2
    @ElementCollection(fetch = FetchType.EAGER)
    @CollectionTable(name = "products_to_orders")
    @MapKeyJoinColumn(name = "product_id")
    @Column(name = "product_quantity")
    private Map<Product, Integer> productQuantityMap;

Answer 1

您选择的JPA提供程序的文档中是否包括如何映射“地图”字段？ 您可以在DataNucleus JPA提供的本文档中看到它的描述。 简单来说，您需要包括

@ElementCollection
@JoinTable
Map<Product, Integer> productQuantityMap;

（以及要配置架构的所有其他注释，但这是必不可少的）。

Answer 2

试试这个配置。 @ElementCollection代替@ManyToMany和@CollectionTable代替@JoinTable

@ElementCollection
@CollectionTable(name = "products_to_orders"        
@MapKeyJoinColumn(name = "product_id")
@Column(name = "product_quantity")
private Map<Product, Integer> productQuantityMap;