子实体中的JPA父外键为空

Question

在一个双向关系中，我不能将子外键与父外键相关联。我有一个父类联盟是这样定义的：

@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);

}

子类ServiceCharge是这样定义的：

@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
}

然后运行测试代码：

    @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);
}

正如您所看到的，在将Union u持久化到数据库之后，我将这两个实体与一个控制器相关联，ServiceController.Add只是通过使用Union setter将实体charge1添加到servicecharges列表中，然后将该实体持久化到数据库中。

不过，测试走对了，但我只能看到这一点：

 | 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 |
 +-----------+----------+----+

如您所见，union_id被设置为NULL。我做错了什么？

Answer 1

尝试首先实例化union类，并在ServiceCharge的构造函数中初始化它。

@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);
}