spring-boot - 无法使用带有自定义对象的地图创建实体对象

Question

弹簧靴 2.5

我有实体Cart。一辆购物车有许多实体Product。在一个购物车中有许多产品。所以我尝试 @JoinColumn但我得到错误：

@Entity
public class Cart {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private int id;
    @OneToMany(mappedBy = "cart", fetch = FetchType.EAGER,
            cascade = CascadeType.ALL)
    private Map<Product, Integer> products;
}


import javax.persistence.*;

@Entity
public class Product {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private int id;
    @ManyToOne(fetch = FetchType.EAGER, optional = false)
    @JoinColumn(name = "cart_id", nullable = false)
    private Cart cart;
}

但是当我尝试运行应用程序时出现错误：

Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'mvcConversionService' defined in class path resource [org/springframework/boot/autoconfigure/web/servlet/WebMvcAutoConfiguration$EnableWebMvcConfiguration.class]: Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.springframework.format.support.FormattingConversionService]: Factory method 'mvcConversionService' threw exception; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'cartRepository' defined in com.myproject.eshop_orders.repo.CartRepository defined in @EnableJpaRepositories declared on JpaRepositoriesRegistrar.EnableJpaRepositoriesConfiguration: Cannot resolve reference to bean 'jpaMappingContext' while setting bean property 'mappingContext'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'jpaMappingContext': Invocation of init method failed; nested exception is org.hibernate.AnnotationException: Use of @OneToMany or @ManyToMany targeting an unmapped class: com.myproject.eshop_orders.api.model.Cart.products[java.lang.Integer]

Answer 1

如果你想要一张地图，你需要使用@MapKeyJoinColumn. 像这样的东西

@Entity
public class Cart {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private int id;

    @MapKeyJoinColumn(name="PRODUCT_ID")
    @OneToMany(mappedBy = "cart", fetch = FetchType.EAGER,
            cascade = CascadeType.ALL)
    private Map<Product, Integer> products;
}

Answer 2

一个购物车有许多不同的产品。我还需要在购物车中存储产品数量（地图中的值）

这是我的解决方案：

@Entity
public class Cart {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private int id;
     @ElementCollection
    @CollectionTable(name = "cart_products", joinColumns = @JoinColumn(name = "cart_id"))
    @MapKeyJoinColumn(name = "product_id")
    @Column(name = "product_qantity")
    private Map<Product, Integer> products;

}


import javax.persistence.*;

@Entity
public class Product {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private int id;
    @ManyToOne(fetch = FetchType.EAGER, optional = false)
    @JoinColumn(name = "cart_id", nullable = false)
    private Cart cart;
}

这是一个正确的解决方案吗？