JPA在子实体中为空的父外键

Question

我无法在OneToMany双向关系中将子外键设置为父项。我有一个父类联盟的定义是这样的：

@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); 

} 

而且这样定义的一个子类ServiceCharge：

@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); 
} 

，你可以看到，在将Union u保存到数据库后，我将两个实体与控制器相关联，ServiceController.add只是使用Union setter将实体charge1添加到servicecharges列表中，然后persis将实体放入数据库中。

然而，测试去正确的，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 | 
+-----------+----------+----+ 

正如你所看到的，union_id设置为null。我究竟做错了什么？

Answer 1

尝试实例化第一个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); 
}