Hibernate学习笔记(十) — HQL查询

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的查询同一时候存在
	 * 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

/**
	 * 查询全部的班级的全部的学生的全部的课程
	 */
	@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();
	}

有用场景:

用户登录系统,推断该用户所拥有的权限。并进行显示权限范围内的菜单

依据username查用户依据用户查角色再依据角色查权限

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，能够採用视图来解决这一问题。使用JDBC拼SQL