Hibernate映射OneToMany+继承

Question

我想知道在订单和请求之间映射的最佳方式。Order类为：

@Entity
@Table(name = "Orders")
public class Order {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private Long id;
}

我有一个类采用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的这个子类，它采用另一个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;
}

我有Request的另一个子类（CancelRequest），它不具有Order属性。

如果我在Order类中放入，那就没有意义了

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

因为订单应该只有一个类型为Collection<Request>的属性。

那么我应该在Order课上放些什么呢？

Answer 1

首先为请求创建一个接口

public interface Request {
   public Long getId();
   public Order getNewOrder();
   public Order getOldorder();
}

然后创建一个抽象的超级类，用于保存继承注释和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;
}

然后创建两个imlpementing类：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，您可以引用Order类中的接口，并将AbstractRequest类作为目标实体。

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