这个类的ids必须手动分配吗？

Question

最近，我在html中更改了表单字段。并根据请求参数更改了servlet中的abit。我没有更改mysql数据库或用户类中的任何内容，也没有更改任何其他hibernate规范。现在我突然发现了这个错误？

我想这和我的@Id是字符串有关吧？但在这些变化之前，这对我来说是很好的。所以我觉得奇怪的是，为什么它会突然开始困扰我，因为我没有改变任何与冬眠相关的东西。

org.hibernate.id.IdentifierGenerationException: ids for this class must be manually assigned before calling save(): com.Tooblo.User
    org.hibernate.id.Assigned.generate(Assigned.java:34)
    org.hibernate.event.internal.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:101)
    org.hibernate.event.internal.DefaultPersistEventListener.entityIsTransient(DefaultPersistEventListener.java:189)
    org.hibernate.event.internal.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:132)
    org.hibernate.event.internal.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:58)
    org.hibernate.internal.SessionImpl.firePersist(SessionImpl.java:774)
    org.hibernate.internal.SessionImpl.persist(SessionImpl.java:747)
    org.hibernate.internal.SessionImpl.persist(SessionImpl.java:752)
    sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    java.lang.reflect.Method.invoke(Unknown Source)
    org.hibernate.context.internal.ThreadLocalSessionContext$TransactionProtectionWrapper.invoke(ThreadLocalSessionContext.java:338)
    com.sun.proxy.$Proxy64.persist(Unknown Source)
    com.Tooblo.DAOImplements.persist(DAOImplements.java:18)
    com.Tooblo.eventHandler.createProfileIndividual(eventHandler.java:226)
    com.Tooblo.eventHandler.doGet(eventHandler.java:70)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:622)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)

我的用户类

@Entity
@Table(name="user")
public class User {


    @GeneratedValue(strategy=GenerationType.AUTO) 
    private long empId;

    @Id
    private String username;
    private String firstname;
    private String lastname;
    private String organisation;
    private String password;
    private String email;

    @ManyToMany( fetch = FetchType.LAZY, cascade = { CascadeType.PERSIST }  )
    @JoinTable(
            name = "user_marker",
            joinColumns = {@JoinColumn(name = "username")},
            inverseJoinColumns = {@JoinColumn(name = "marker_id")})
    private Set<Marker> bookmarks = new HashSet<>();

    public User() {

    }

    public User(String username, String password, String email) {
        this.username = username;
        this.password = password;
        this.email = email;
    }

...Setters和getters或已发送。

我的servlet方法。

        String username = request.getParameter("username");
        String password = request.getParameter("password");
        String email = request.getParameter("email");

        User user = new User(username, password, email);

        DAO.persist(user);

我坚持的方法在我的刀

@Override
    public void persist(Object entity) {
        session = HibernateUtil.getSessionFactory().getCurrentSession();    
        session.beginTransaction();
        session.persist(entity);
        session.getTransaction().commit();
    }

Answer 1

由于您使用的是mysql服务器，所以它不支持AUTO_INCREMENT的非主键属性，您的主键是用户名。

因此，您可以在实体类和DB架构中将主键更改为empId字段。

@Id
@GeneratedValue(strategy=GenerationType.AUTO) 
private long empId;