hibernate HQL

1.HQL

HQL是Hibernate Query Language的缩写，HQL的语法很像SQL的语法，

但HQL是一种面向对象的查询语言。因此，SQL的操作对象是数据表和列等数据对象，

而HQL的操作对象是类、实例、属性等

List list =session.createQuery("from Dept").list();
		System.out.println(list.size());

返回一个数组

List<Object[]> list = session.createQuery(
				"select d.dname,1 from Dept as d").list();
		System.out.println(list.get(0)[0]);

返回一个类型，查询单列

List<String> list = session.createQuery(
				"select d.dname from Dept as d").list();
		System.out.println(list.get(0));

返回一个对象 uniqueResult() 查询出来必须是一条

Dept dept = (org.ymm.entity.Dept) session.createQuery(
				"select d from Dept as d where d.deptno=10").uniqueResult();
		System.out.println(dept.getDname());

语句中传参（?）和（：名字）

Query q= session.createQuery(
				"select d from Dept as d where d.deptno=?");
		q.setString(0,"10");
		Dept d= (Dept) q.uniqueResult();
		System.out.println(d.getDname());

Query q= session.createQuery(
				"select d from Dept as d where d.deptno=:dno");
		q.setString("dno", "10");
		Dept d= (Dept) q.uniqueResult();
		System.out.println(d.getDname());

多表查询 笛卡儿积，表连接

Query q= session.createQuery(
				"from Dept as d,Emp as e where d.deptno =e.dept.deptno");
		List<Object[]> list= q.list();//得到数据储存两个表数据的数组
		for (int i = 0; i < list.size(); i++) {
			Object[] o = list.get(i);
			Dept d=(Dept)o[0];
			Emp e=(Emp)o[1];
			System.out.println("部门name："+d.getDname()+"\t\t员工name："+e.getEname());
		}

Query q= session.createQuery(
				"select d,1 from Dept as d right join d.emps");
		List<Object[]> list= q.list();
		for (int i = 0; i < list.size(); i++) {
			Object[] o = list.get(i);
			Dept d=(Dept)o[0];
			//Emp e=(Emp)o[1];
			System.out.println("部门name："+d.getDname());
		}