Question

是否可以拥有收藏地图？使用下面的代码，用户有一些购买，但我想映射它，因此产品实体（或产品ID）是关键，价值是所有类型产品的购买。

@Entity
public class User {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @OneToMany(fetch = FetchType.LAZY, cascade = CascadeType.ALL, targetEntity = Purchase.class, orphanRemoval = true)
    @JoinColumn(name = "user_id", updatable = false)
    @MapKeyColumn(name = "product_id")
    private Map<Long, List<Purchase<Product>>> purchases = new HashMap<>();

}

@Entity
public class Product {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

}

@Entity
public class Purchase<T extends Product> implements Serializable {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    Long id;

    @ManyToOne
    @JoinColumn(name = "user_id", referencedColumnName = "id")
    private User user;

    @ManyToOne(targetEntity = Prodect.class)
    @JoinColumn(name = "product_id", referencedColumnName = "id")
    private T product;

    @Column(name = "purchase_date")
    private Date purchaseDate;

}

异常;

org.springframework.orm.hibernate3.HibernateSystemException: could not get a field value by reflection getter of test.domain.Purchase.id; nested exception is org.hibernate.PropertyAccessException: could not get a field value by reflection getter of test.domain.Purchase.id
...
Caused by: org.hibernate.PropertyAccessException: could not get a field value by reflection getter of test.domain.Purchase.id
...
Caused by: java.lang.IllegalArgumentException: Can not set java.lang.Long field test.domain.Purchase.id to java.util.ArrayList

Answer 1

JSR317v2.0中的规范仅考虑

的地图集合

基本类型
嵌入式
实体。

在地图的键和值部分，似乎

private Map<Long, List<Purchase<Product>>> purchases = new HashMap<>();

对于规范而言，它更复杂。

根据您的要求考虑这样的事情。

但是我想映射它以便产品实体（或产品ID）是关键，并且值是所有类型产品的购买。

private Map<Product, Purchase> purchases

并使用@MapKey

MapKey注释用于指定特殊情况 map键本身就是主键或持久字段或属性作为地图价值的实体。 MapKeyClass注释是指定MapKey时未使用。

注意： @MapKeyColumn（name =“product_id”）只会让列名称对所需的配置不起作用，只需在表格中给出列名称，

JPA，Hibernate，使用@MapKeyColumn的集合映射

1 个答案: