HQL简单demo

最新推荐文章于 2020-05-23 17:10:21 发布

原创最新推荐文章于 2020-05-23 17:10:21 发布 · 262 阅读

CC 4.0 BY-SA版权

HQL作为面向对象的查询语言，是Hibernate推荐的查询方式。本文深入探讨了HQL的使用，包括别名指定、投影查询、动态实例查询、条件查询（按位置和名字）以及分页查询等核心概念。

HQL是面向对象的查询语言，它和SQL查询语言有些相似，但它使用的是类、对象和属性的概念，而没有表和字段的概念。在Hibernate提供的各种检索方式中，HQL是官方推荐的查询语言，也是使用最广泛的一种检索方式。本文将对HQL几种常用的方式进行讲解。

指定别名

@Test
	public void aliasTest(){
		
			// TODO Auto-generated method stub
			SessionFactory sf = null;		
			Session session = null;
			Transaction ts = null;		
			try {
	  			sf = HibernateUtil.getSessionFactory();
				session = sf.getCurrentSession();
				ts = session.beginTransaction();			
				String hql = "from Person as p where p.name ='shi'";
				Query query = session.createQuery(hql);
				List<Person> ps=query.list();
				for (Person person : ps) {
					System.out.println(person.toString());
				}
			} catch (HibernateException e) {
				// TODO Auto-generated catch block
				if(ts != null)
				{
					ts.rollback();
				}
				e.printStackTrace();
			}
		}

投影查询

@Test
	public void portionQueryTest(){

	// TODO Auto-generated method stub
	SessionFactory sf = null;		
	Session session = null;
	Transaction ts = null;		
	try {
			sf = HibernateUtil.getSessionFactory();
		session = sf.getCurrentSession();
		ts = session.beginTransaction();			
		String hql = "select p.name,p.sex from Person as p";
		Query query = session.createQuery(hql);
		List<Object[]> list=query.list();
		Iterator it = list.iterator();
		while(it.hasNext())
		{
			Object[] obj = (Object[]) it.next();
			System.out.println(obj[0]+"  "+obj[1]);
		}
	} catch (HibernateException e) {
		// TODO Auto-generated catch block
		if(ts != null)
		{
			ts.rollback();
		}
		e.printStackTrace();
	}
}

动态实例查询

@Test
	public void dynamicQueryTest(){

		// TODO Auto-generated method stub
		SessionFactory sf = null;		
		Session session = null;
		Transaction ts = null;		
		try {
				sf = HibernateUtil.getSessionFactory();
			session = sf.getCurrentSession();
			ts = session.beginTransaction();			
			String hql = "select new Person(p.name,p.sex)from Person as p";
			Query query = session.createQuery(hql);
			@SuppressWarnings("deprecation")
			Object count=query.uniqueResult();
			List<Person> list=query.list();
			for (Person p : list) {
				System.out.println(p.getName()+"  "+p.getSex());
			}
		} catch (HibernateException e) {
			// TODO Auto-generated catch block
			if(ts != null)
			{
				ts.rollback();
			}
			e.printStackTrace();
		}
	}

条件查询（按参数位置查询）

@Test
	public void paraQueryTest1(){
	// TODO Auto-generated method stub
	SessionFactory sf = null;		
	Session session = null;
	Transaction ts = null;		
	try {
			sf = HibernateUtil.getSessionFactory();
		session = sf.getCurrentSession();
		ts = session.beginTransaction();			
		String hql = "from Person where name like ?";
		Query query = session.createQuery(hql);
		query.setString(0, "%er%");
		List<Person> list=query.list();
		for (Person p : list) {
			System.out.println(p.toString());
		}
	} catch (HibernateException e) {
		// TODO Auto-generated catch block
		if(ts != null)
		{
			ts.rollback();
		}
		e.printStackTrace();
	}

条件查询（按参数名字查询）

@Test
	public void paraQueryTest2(){

	// TODO Auto-generated method stub
	SessionFactory sf = null;		
	Session session = null;
	Transaction ts = null;		
	try {
			sf = HibernateUtil.getSessionFactory();
		session = sf.getCurrentSession();
		ts = session.beginTransaction();			
		String hql = "from Person where id=:id";
		Query query = session.createQuery(hql);
		query.setParameter("id",4);
		List<Person> list=query.list();
		for (Person p : list) {
			System.out.println(p.toString());
		}
	} catch (HibernateException e) {
		// TODO Auto-generated catch block
		if(ts != null)
		{
			ts.rollback();
		}
		e.printStackTrace();
	}
	
}

分页查询

@Test
	public void paraPageTest2(){

	// TODO Auto-generated method stub
	SessionFactory sf = null;		
	Session session = null;
	Transaction ts = null;		
	try {
			sf = HibernateUtil.getSessionFactory();
		session = sf.getCurrentSession();
		ts = session.beginTransaction();			
		String hql = "from Person";
		Query query = session.createQuery(hql);
		query.setFirstResult(1);
		query.setMaxResults(2);
		List<Person> list=query.list();
		for (Person p : list) {
			System.out.println(p.toString());
		}
	} catch (HibernateException e) {
		// TODO Auto-generated catch block
		if(ts != null)
		{
			ts.rollback();
		}
		e.printStackTrace();
	}
	
}