将@OneToMany 关系映射为主键作为外键

Question

我正在尝试在 JPA 中映射下图中描述的一对多表关系：

如可以看到的，"activity_property"表使用与复合主键(id,name)和列"id"是一个外键列"id"在表中"activity"。

我当前的实体是这样映射的（为了清楚起见，省略了一些辅助方法）：

活动.java

@Entity
@Getter
@Setter
public class Activity {
   @Id
   @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "act_id_generator")
   @SequenceGenerator(name = "act_id_generator", sequenceName = "activity_id_seq", allocationSize = 1, initialValue = 1)
   private Integer id;

   private String name;

   @OneToMany(mappedBy = "id.activityId", cascade = CascadeType.ALL, orphanRemoval = true)
   private List<ActivityProperty> properties;
}

活动属性.java

@Entity
@Getter
@Setter
@Table(name = "activity_property")
public class ActivityProperty {
    @EmbeddedId
    private ActivityPropertyId id;

    private String value;

    @Enumerated(EnumType.STRING)
    private PropertyType type;
}

ActivityPropertyId.java

@Embeddable
@Getter
@Setter
@ToString
public class ActivityPropertyId implements Serializable {

    @Column(name = "id")
    private Integer activityId;

    private String name;

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        ActivityPropertyId that = (ActivityPropertyId) o;
        return activityId.equals(that.activityId) &&
                name.equals(that.name);
    }

    @Override
    public int hashCode() {
        return Objects.hash(activityId, name);
    }
}

当我尝试以这种方式坚持一项活动时：

Activity activity = createActivity("Activity_1");
activity.addProperty(ActivityProperty.from("Prop1", "value1", PropertyType.PARAMETER));
activityDAO.persist(activity);

我可以在 Hibernate 中看到以下痕迹：

Hibernate: call next value for activity_id_seq
Hibernate: insert into activity (name, id) values (?, ?)
Hibernate: insert into activity_property (type, value, id, name) values (?, ?, ?, ?)
05-05-2019 12:26:29.623 [main] WARN  o.h.e.jdbc.spi.SqlExceptionHelper.logExceptions - SQL Error: 23502, SQLState: 23502
05-05-2019 12:26:29.624 [main] ERROR o.h.e.jdbc.spi.SqlExceptionHelper.logExceptions - NULL not allowed for column "ID"; SQL statement:
insert into activity_property (type, value, id, name) values (?, ?, ?, ?) [23502-199]

似乎自动生成的 idActivity没有用于ActivityProperty.

我不知道如何正确映射这种关系。我的 JPA 注释中是否缺少任何内容？

Answer 1

据我所知，JPA 不支持通过cascade操作来实现这一点。你对JPA的要求太高了。我没有具体的参考资料来说明这一点，但您可以使用下面的代码尽可能接近。它不会运行，因为 hibernate（至少）不知道如何自动将 映射activity.id到类的 PK ActivityProperty。

@Entity
@Getter
@Setter
@Table(name = "activity_property")
@IdClass(ActivityPropertyId.class)
public class ActivityProperty {
    @ManyToOne
    @Id
    @JoinColumn(name="id", referencedColumnName="id")
    private Activity activity;

    @Id
    private String name;
    private String value;

}

@Getter
@Setter
@ToString
public class ActivityPropertyId implements Serializable {
    public ActivityPropertyId() {}

    @Column(name = "id")
    private Integer activity;

    private String name;

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        ActivityPropertyId that = (ActivityPropertyId) o;
        return activity.equals(that.activity) &&
                name.equals(that.name);
    }

    @Override
    public int hashCode() {
        return Objects.hash(activity, name);
    }
}

这将给出例外

引起原因：java.lang.IllegalArgumentException：无法将 java.lang.Integer 字段 model.ActivityPropertyId.activity 设置为 model.Activity

我还没有看到任何解决这个问题的好方法。恕我直言，cascade这是一个傻瓜的天堂，您应该ActivityProperty自己保存实例并仅使用双向映射进行查询。这确实是它的用途。如果您OneToMany通过级联对列表执行一些简单的保存操作并查看生成的 SQL，您会看到可怕的事情。