Hibernate学习笔记 — HQL查询

Posted 2022-11-21 品尝这杯浓咖啡

一、HQL的一对多查询

班级(1)->(多)学生

/**
	 * 实现Classes与Student的内连接
	 * 
	 * SELECT c.*,s.*
	 * from classes c INNER JOIN student s 
	 * where (c.cid=s.cid)
	 */
	@Test
	public void testInnerJoin()
		session = HibernateUtils.openSession();
		
		Query query = session.createQuery("from Classes c " +
				"inner join c.students s ");
		List list = query.list();//Object[]
		session.close();
	
	
	/**
	 * 迫切内连接
	 */
	@Test
	public void testInnerJoin_fetch()
		session = HibernateUtils.openSession();
		
		Query query = session.createQuery("from Classes c " +
				"inner join fetch c.students s ");
		List list = query.list();//Classes
		session.close();
	
	
	/**
	 * 左外连接
	 * SELECT c.*,s.*
	 * from classes c LEFT OUTER JOIN student s 
	 * on(s.cid=c.cid)
	 */
	@Test
	public void testLeftOutJoin()
		session = HibernateUtils.openSession();
		
		Query query = session.createQuery("from Classes c " +
				"left outer join c.students s ");
		List list = query.list();//Object[]
		session.close();
	
	/**
	 * 迫切左外连接
	 * 
	 */
	@Test
	public void testLeftOutJoin_fetch()
		session = HibernateUtils.openSession();
		
		Query query = session.createQuery("from Classes c " +
				"left outer join fetch c.students s ");
		List list = query.list();//Classes
		session.close();
	
	
	/**
	 * 要查询的属性来自两个持久化类
	 * 	注意:带构造函数的查询不能 与 带fetch的查询同时存在
	 * 使用 fetch:是希望带Classes
	 * 	
	 */
	@Test
	public void testQueryPropertyFromTwo()
		session = HibernateUtils.openSession();
		List<ClassStuView> classStuViews = session.createQuery("select new cn.cil.domain.ClassStuView(c.name,s.name) " +
				" from Classes c inner join c.students s").list();
		session.close();
	

二、HQL的多对多查询

学生(多)->(多)课程

/**
	 * 迫切内连接
	 *     
	 */
	@Test
	public void testInnerJoin_Fetch()
		Session session = sessionFactory.openSession();
		session.createQuery("from Student s inner join fetch s.courses c").list();
		session.close();
	
	
	/**
	 * 迫切左外连接
	 */
	@Test
	public void testLeftOuterJoin_Fetch()
		Session session = sessionFactory.openSession();
		session.createQuery("from Student s left outer join fetch s.courses c").list();
		session.close();
	

三、一对多与多对多结合

班级(1)->(多)学生->(多)课程

/**
	 * 查询所有的班级的所有的学生的所有的课程
	 */
	@Test
	public void testQuery1()
		Session session = HibernateUtils.openSession();
		List<Classes> classes = session.createQuery("from Classes c inner join " +
											"fetch c.students s inner join " +
											"fetch s.courses cc").list();
		session.close();
	
	
	@Test
	public void testQuery2()
		Session session = HibernateUtils.openSession();
		List<Student> classes = session.createQuery("from Student s inner join fetch s.classes c inner join fetch s.courses cc").list();
		session.close();
	

实用场景:

用户登录系统,判断该用户所拥有的权限，并进行显示权限范围内的菜单

根据username查用户根据用户查角色再根据角色查权限

createQuery("from Privilege p inner join fetch p.roles r inner join fetch r.users u where u.username=?")

当表与表之间的关系过于复杂的时候，就不能使用hibernate了,hql的书写会相当相当麻烦，可以采用视图来解决这一问题，使用JDBC拼SQL