我在hibernate介绍性项目中遇到了NonUniqueObjectException错误

Question

我是Java Hibernate的新手。我在我的代码中得到了以下错误。我正在尝试实现多对多关系，我在谷歌上搜索并理解了这个概念，但我无法为像我这样的初学者找到合适的实现。提前谢谢。

Students.java

@Entity
@Table
public class Students 
{
    
    @Id
    private int roll_no;
    private float marks;
    private String name;
    
    @ManyToMany(cascade = { CascadeType.ALL })
    @JoinTable(
            name = "mobiles_students", 
            joinColumns = { @JoinColumn(name = "roll_no") }, 
            inverseJoinColumns = { @JoinColumn(name = "mob_id") }
            )
    private List<Mobiles> mobile = new ArrayList<Mobiles>();
            // Getters, Setters

Mobiles.java

@Entity
public class Mobiles 
{
    @Id
    private int mob_id;
    private String mobile;
    
    @ManyToMany(mappedBy = "mobile")
    private List<Students> studs = new ArrayList<Students>();
    // Getters, Setters

App.java

public class App 
{
    public static void main( String[] args )
    {
        
        Configuration con = new Configuration().configure().addAnnotatedClass(Students.class).addAnnotatedClass(Mobiles.class);
        SessionFactory factory = con.buildSessionFactory();
        Session session = factory.openSession();
        Transaction t = session.beginTransaction();
        
        
        Mobiles mobile1  = new Mobiles();
        mobile1.setMob_id(3);
        mobile1.setMobile("Redmi K20");
        

        Mobiles mobile2  = new Mobiles();
        mobile2.setMob_id(3);
        mobile2.setMobile("Nokia 6.1 Plus");
        

        Students stud1 = new Students();
        stud1.setRoll_no(3);
        stud1.setMarks(100);
        stud1.setName("Vivek");
        
        List<Mobiles> mob = new ArrayList<Mobiles>();
        mob.add(mobile1);
        mob.add(mobile2);
        stud1.setMobile(mob);
//      stud1.getMobile().add(mobile1);
//      stud1.getMobile().add(mobile2);
//      mobile1.getStuds().add(stud1);      
//      mobile2.getStuds().add(stud1);
    
        
        
//      Students stud = (Students)session.get(Students.class, 1);
        session.save(mobile1);
        session.save(mobile2);
        session.save(stud1);
        t.commit();
//      System.out.println(stud);
    }
}

错误

INFO: HHH000490: Using JtaPlatform implementation: [org.hibernate.engine.transaction.jta.platform.internal.NoJtaPlatform]
Exception in thread "main" org.hibernate.NonUniqueObjectException: A different object with the same identifier value was already associated with the session : [com.vivek.NewJavaApp.Mobiles#3]
    at org.hibernate.event.internal.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:180)
    at org.hibernate.event.internal.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:135)
    at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.saveWithGeneratedOrRequestedId(DefaultSaveOrUpdateEventListener.java:194)
    at org.hibernate.event.internal.DefaultSaveEventListener.saveWithGeneratedOrRequestedId(DefaultSaveEventListener.java:38)
    at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.entityIsTransient(DefaultSaveOrUpdateEventListener.java:179)
    at org.hibernate.event.internal.DefaultSaveEventListener.performSaveOrUpdate(DefaultSaveEventListener.java:32)
    at org.hibernate.event.internal.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:75)
    at org.hibernate.event.service.internal.EventListenerGroupImpl.fireEventOnEachListener(EventListenerGroupImpl.java:102)
    at org.hibernate.internal.SessionImpl.fireSave(SessionImpl.java:634)
    at org.hibernate.internal.SessionImpl.save(SessionImpl.java:627)
    at org.hibernate.internal.SessionImpl.save(SessionImpl.java:622)
    at com.vivek.NewJavaApp.App.main(App.java:52)

Answer 1

在您的Mobiles实体类字段中，mob_id被标注为@Id。使用@Id注释的字段通常应该被赋予一个惟一的值(通常也可以通过自动生成该值)。在主应用程序App.java中，您需要手动将mob_id属性设置为相同的值3两次。这会导致引发NonUniqueObjectException。