子實體中的JPA空父外鍵

Question

我無法在OneToMany雙向關系中將子級外鍵與父級關聯。 我有一個以此類定義的父類Union：

@Entity
@PrimaryKeyJoinColumn(referencedColumnName="id")
@Table(name="union_tb")
@Inheritance( strategy = InheritanceType.JOINED )     
public class Union extends User{

@Column(unique=true)
String Name;
float uniondue = 0;


@OneToMany(targetEntity=ServiceCharge.class,cascade=CascadeType.REMOVE, orphanRemoval=true,fetch = FetchType.EAGER,mappedBy="union")
List<ServiceCharge> ServiceCharges;
@OneToMany(targetEntity=Employee.class,cascade=CascadeType.REMOVE, orphanRemoval=true,fetch = FetchType.EAGER)
List<Employee> Employee;

public void PostServiceCharge(ServiceCharge charge) {
    ServiceCharges.add(charge);

}

子類ServiceCharge定義了這種方式：

@Entity
@Table
 public class ServiceCharge implements Serializable{


@Id @GeneratedValue(strategy= GenerationType.AUTO)
int ChargeID;
String Service;
@Temporal(TemporalType.TIMESTAMP)
Calendar  TimeStamp;
float ChargeAmount;
@ManyToOne
@JoinColumn(name="union_id")
Union union;

public ServiceCharge(){super();}




public ServiceCharge(float chargeAmount, String service, String timestamp/*, Union union*/) throws ParseException {
    super();
    ChargeAmount = chargeAmount;
    Service = service;
    TimeStamp = TimeManagUtil.getGCobjectfromString(timestamp);
    //this.Union = union;
}

// getters and setters
}

然后我運行測試代碼：

    @Test
public void Test() throws Exception {
    ServiceCharge charge1 = new ServiceCharge(60,"service for employee","27/11/2016 20:35:00");
    Union u = new Union("Sindacate", 80);
    UnionController.add(u);
    ServiceController.add(charge1, u);
}

如您所見，在將Union u持久化到數據庫后，我將兩個實體與一個控制器相關聯，ServiceController.add僅通過使用Union setter將實體charge1添加到服務收費列表中，然后將該實體持久化到數據庫中。

但是，測試正常進行，但是我只能看到以下內容：

 | ChargeID | ChargeAmount | Service              | TimeStamp           | union_id |
 +----------+--------------+----------------------+---------------------+----------+
 |        6 |           60 | service for employee | 2016-11-27 20:35:00 |     NULL |
 |        7 |           10 | service for employee | 2016-11-27 20:45:00 |     NULL


 | Name      | uniondue | id |
 +-----------+----------+----+
 | Sindacate |       80 |  5 |
 +-----------+----------+----+

如您所見，union_id設置為null。 我究竟做錯了什么？

Answer 1

嘗試首先實例化Union類，然后在ServiceCharge的構造函數中對其進行初始化。

@Test
public void Test() throws Exception {
    Union u = new Union("Sindacate", 80);
    UnionController.add(u);
    ServiceCharge charge1 = 
              new ServiceCharge(60,"service for employee","27/11/2016 20:35:00", u); // uncomment your parameter here that accepts Union class type.
    ServiceController.add(charge1, u);
}