休眠映射OneToMany +繼承

Question

我想知道在我的訂單和請求之間映射的最佳方式。 的Order類是：

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

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

} 

我有一個類，帶有一個Order屬性

@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這個子類，另需Order屬性

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

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

而且我有另一個子類（CancelRequest）Request wh ich不需要Order屬性。

它沒有意義，如果在Order類我把：

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

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

因爲一個訂單隻能有一個Collection<Request>類型的屬性。

那麼我應該在我的Order課上放什麼？

Answer 1

首先讓一個接口，用於請求

public interface Request { 

    public Long getId(); 

    public Order getNewOrder(); 

    public Order getOldorder(); 
} 

然後作出一個抽象的超類用於保存繼承註釋和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; 
} 

然後做兩個imlpementing類：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; 
    } 
} 

然後你可以只引用從Order類的接口與AbstractRequest類爲目標的實體。

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