Hibernate 映射 OneToMany + 继承

Question

我想知道在我的订单和请求之间映射的最佳方式。 Order class 是：

@Entity
@Table(name = "Orders")
public class Order {

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

}

我有一个 class 具有 Order 属性

@Entity
@Table(name = "Requests")
@Inheritance(strategy=InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name="request_type",discriminatorType=DiscriminatorType.STRING)
public class Request {

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

@ManyToOne(targetEntity = Order.class, fetch = FetchType.EAGER)
@JoinColumn(name = "oldOrder_id", referencedColumnName = "id")
private Order oldOrder;
}

我有 Request 的这个子class，它带有另一个 Order 属性

@Entity
@DiscriminatorValue("Edit")
public class EditRequest extends Request {

@ManyToOne(targetEntity = Order.class, fetch = FetchType.EAGER)
@JoinColumn(name = "newOrder_id", referencedColumnName = "id")
private Order newOrder;
}

我还有 Request 的另一个子 class (CancelRequest)，它没有 Order 属性。

如果在 Order class 中输入 :

就没有意义

@OneToMany(mappedBy="oldOrder")
private Collection<Request> requests;

@OneToMany(mappedBy="newOrder")
private Collection<EditRequest> editRequests;

因为一个订单应该只有一个 Collection<Request> 类型的属性。

那么我应该在 Order class 中输入什么？

Answer 1

先为Request做一个接口

public interface Request {

   public Long getId();

   public Order getNewOrder();

   public Order getOldorder();
}

然后创建一个抽象的超级class来保存继承注解和id字段。

@Entity
@Table(name = "Requests")
@Inheritance(strategy=InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name="request_type",discriminatorType=DiscriminatorType.STRING)
public class AbstractRequest {

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

然后做两个实现classes：EditRequest和CancelRequest

@Entity
@DiscriminatorValue("Edit")
public class EditRequest extends AbstractRequest implements Request {

   @ManyToOne(targetEntity = Order.class, fetch =FetchType.EAGER)
   private Order newOrder;

   @ManyToOne(targetEntity = Order.class, fetch =FetchType.EAGER)
   private Order oldOrder;

   public Order getNewOrder() {
      return neworder;
   }

   public Order getOldOrder() {
      return oldOrder;
   }
}

@Entity
@DiscriminatorValue("Cancel")
public class CancelRequest extends AbstractRequest implements Request {

   public Order getNewOrder() {
      return null;
   }

   public Order getOldOrder() {
      return null;
   }
}

然后您可以只引用 Order class 中的接口，并将 AbstractRequest class 作为目标实体。

@OneToMany(mappedBy="order" targetEntity = AbstractRequest.class, fetch = FetchType.EAGER)
private Collection<Request> requests;

Hibernate 映射 OneToMany + 继承

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