hql查詢是基於對象的查詢，不是基於表的查詢。

1.hql的簡單查詢

    @Test
    public void queryUsers() {
        //簡單查詢
        SessionFactory sf = null;
        Session s = null;
        Transaction t = null;
        try {
            sf = HibernateUtil.getSessionFactory();
            s = sf.getCurrentSession();
            t 
 
= s.beginTransaction();
            Query<User> query = s.createQuery("from User");
            
            List<User> users = query.list();
            for(User user:users){
                System.out.println(user);
            }
            t.commit();
        }catch(Exception e) {
            
 
if(t!=null) {
                t.rollback();
            }
            e.printStackTrace();
        }
    }

其中“from User”是hql語句，User是實體類User類，而不是User表

此實例測試結果

數據庫內容

2.屬性查詢

@Test
    public void queryUsernames() {
        //屬性查詢
        SessionFactory sf = null;
        Session s = null;
        Transaction t 
 
= null;
        
        try {
            sf = HibernateUtil.getSessionFactory();
            s = sf.getCurrentSession();
            t = s.beginTransaction();
            Query<User> query = s.createQuery("select u.username from User u");
            List usernames = query.list();
            
            for(Object username:usernames){
                System.out.println(username);
            }
            t.commit();
        }catch(Exception e) {
            if(t!=null) {
                t.rollback();
            }
            e.printStackTrace();
        }
    }

測試結果

3.實例化查詢

@Test
    public void queryNewUser() {
        //實例化查詢
        SessionFactory sf = null;
        Session s = null;
        Transaction t = null;
        
        try {
            sf = HibernateUtil.getSessionFactory();
            s = sf.getCurrentSession();
            t = s.beginTransaction();
            Query<User> query = s.createQuery("select new User(u.id,u.username,u.password,u.sex,u.age) from User u");
            List<User> users = query.list();
            
            for(User user:users){
                System.out.println(user);
            }
            t.commit();
        }catch(Exception e) {
            if(t!=null) {
                t.rollback();
            }
            e.printStackTrace();
        }
    }

對對象進行實例化

測試結果

第五次作業 hql查詢