java - 坚持 GAE 后将子实体添加到父实体

Question

我有一个父实体客户端。该客户可以访问该网站并创建约会。这意味着约会是在客户反对的其他时间创建的。

我的问题是:如何将子对象添加到已持久化的父对象中？如果调用下面示例中的函数 addData1()，则会创建一个约会表并添加一个条目。当调用函数 addData2() 时，不会发生这种情况。

当您在关闭实体管理器后更新持久对象时，这不是也会在表中更新吗？

@Entity
public class Client{
    @Id
    private String name;
    @OneToMany(cascade = CascadeType.ALL)
    private Set<Appointment> appointments;
}

@Entity
public class Appointment{
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Key id;
}

// This works
public function addData1(){
    EntityManager em = EMF.get().createEntityManager();
    Client client = new Client(name);
    for(Appointment a  : newAppointments)
        client.addAppointment(a);
    em.persist(client);
    em.close();
}

// This doesn't work.
public function addData2(){
    EntityManager em = EMF.get().createEntityManager();
    Client client = new Client(name);
    em.persist(client);
    em.close();
    for(Appointment a  : newAppointments)
        client.addAppointment(a);
}

Answer 1

public function addData1(){
    EntityManager em = EMF.get().createEntityManager();
    Client client = new Client(name);
    for(Appointment a  : newAppointments)
        client.addAppointment(a);
    em.persist(client);
    em.close();
}

此函数之所以有效，是因为您保留了所有对象。

// This doesn't work.
public function addData2(){
    EntityManager em = EMF.get().createEntityManager();
    Client client = new Client(name);
    em.persist(client);
    em.close();    <--- You persist client with no appointment
    for(Appointment a  : newAppointments)
        client.addAppointment(a);   <-- those entitys are detached entity ( not persisted)
}

这个函数不会，因为你试图用分离的实体来持久化一个对象

你应该得到这样的异常:

Caused by: org.hibernate.PersistentObjectException: detached entity passed to persist: com.test.Appointment

如果你想避免这个异常，可以尝试以下方法:

public void addData2(List<Appointment> newAppointments){
    Client client = new Client();
    client.setName("name1");
    entityManager.persist(client);
    for(Appointment a  : newAppointments)
        client.addAppointment(a);
    entityManager.merge(client);
    entityManager.close();
}

顺便说一句，尝试无效使用名称作为 Id