【06-17】开发中遇到的异常

hibernate：

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bug:

　　Batch update returned unexpected row count from update [0]; actual row count: 0; expected: 1

solution:

　　hibernate在执行save(Object obj)时，如果obj的主键不为空，则会去update而不是save操作，此时如果obj的主键不为空，但是在数据库中查不到时则会抛出该异常，因此save时可以显示将主键字段设为Null。

　　也有可能是有级联关系的对象没有保存过，在save时

bug:

　　a different object with the same identifier value was already associated with the session

solution:

　　

bug:

　　identifier of an instance of ... is alterde from 150 to null

solution:

　　

bug:

　　org.hibernate.MappingException: Unknown entity

solution:

　　我用的是hibernate5，使用sessionFactory=new Configuration().configure().buildSessionFactory();能够获取到sessionFactory但是hibernate却找不到注解的实体类，抛出MappingException，使用以下方法才能够获取到注解类。

    public static SessionFactory sessionFactory;
    static{
//        Configuration cfg= new Configuration();
//        cfg.addClass(Person.class);
//        cfg.addClass(Phone.class);
//        cfg.addAnnotatedClass(entity.Person.class);
//        cfg.addAnnotatedClass(entity.Phone.class);
//        sessionFactory=new Configuration().configure().buildSessionFactory();
        final StandardServiceRegistry registry = new StandardServiceRegistryBuilder()
                .configure() // configures settings from hibernate.cfg.xml
                .build();
        try {
            sessionFactory = new MetadataSources( registry ).buildMetadata().buildSessionFactory();
        }
        catch (Exception e) {
            // The registry would be destroyed by the SessionFactory, but we had trouble building the SessionFactory
            // so destroy it manually.
            StandardServiceRegistryBuilder.destroy( registry );
        }
        
    }

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