【HQL】属性查询、条件查询

单一属性：

//返回结果集属性列表，元素类型和实体类中的属性类型一致
            List students = session.createQuery("select name from Student").list();
            for (Iterator iter=students.iterator(); iter.hasNext();) {
                String name = (String)iter.next();
                System.out.println(name);
            }

多个属性：

//查询多个属性，返回对象数组集合
            //数组元素的类型与查询的属性类型一致
            //数组的长度与select中查询的属性个数一致
            List students = session.createQuery("select id, name from Student").list();
            for (Iterator iter=students.iterator(); iter.hasNext();) {
                Object[] obj = (Object[])iter.next();
                System.out.println(obj[0] + ", " + obj[1]);
            }

多个属性查询,返回Student：

//可以使用hql返回Student对象
            //需要提供构造函数
            List students = session.createQuery("select new Student(id, name) from Student").list();
            for (Iterator iter=students.iterator(); iter.hasNext();) {
                Student student = (Student)iter.next();
                System.out.println(student.getId() + ", " + student.getName());
            }

可以使用别名：

// 可以使用别名
            List students = session.createQuery("select s.id, s.name from Student s").list();
            for (Iterator iter=students.iterator(); iter.hasNext();) {
                Object[] obj = (Object[])iter.next();
                System.out.println(obj[0] + ", " + obj[1]);
            }

实体对象查询：

//返回Student对象的集合
            //可以忽select关键字
            List students = session.createQuery("from Student").list();
            for (Iterator iter=students.iterator(); iter.hasNext();) {
                Student student = (Student)iter.next();
                System.out.println(student.getName());
            }

//返回Student对象的集合
            //可以忽select关键字，可以加入别名
            List students = session.createQuery("from Student s").list();
            for (Iterator iter=students.iterator(); iter.hasNext();) {
                Student student = (Student)iter.next();
                System.out.println(student.getName());
            }

//返回Student对象的集合
            //如果使用select查询实体对象，必须使用别名
            List students = session.createQuery("select s from Student s").list();
            for (Iterator iter=students.iterator(); iter.hasNext();) {
                Student student = (Student)iter.next();
                System.out.println(student.getName());
            }

条件查询

//可以拼串
            List students = session.createQuery("select s.id, s.name from Student s where s.name like '%0%'").list();
            for (Iterator iter=students.iterator(); iter.hasNext();) {
                Object[] obj = (Object[])iter.next();
                System.out.println(obj[0] + ", " + obj[1]);
            }

//可以使用？方式传递参数
            //索引从0开始，不同于jdbc从1开始
            //值能使用单引号引起来
            //List students = session.createQuery("select s.id, s.name from Student s where s.name like ?").list();
//            Query query  = session.createQuery("select s.id, s.name from Student s where s.name like ?");
//            query.setParameter(0, "%0%");
//            List students = query.list();
            
            //方法链编程，建议采用此种方式
            List students = session.createQuery("select s.id, s.name from Student s where s.name like ?")
                    .setParameter(0, "%0%")
                    .list();
            for (Iterator iter=students.iterator(); iter.hasNext();) {
                Object[] obj = (Object[])iter.next();
                System.out.println(obj[0] + ", " + obj[1]);
            }

//可以采用 :参数名 的方式传递参数
            List students = session.createQuery("select s.id, s.name from Student s where s.name like :myname")
                    .setParameter("myname",  "%0%")
                    .list();
            for (Iterator iter=students.iterator(); iter.hasNext();) {
                Object[] obj = (Object[])iter.next();
                System.out.println(obj[0] + ", " + obj[1]);
            }

//采用 ？方式，查询学号为1,2,3,4,5的学生
            List students = session.createQuery("select s.id, s.name from Student s where s.id in(?, ?, ?, ?, ?)")
                    .setParameter(0, 1)
                    .setParameter(1, 2)
                    .setParameter(2, 3)
                    .setParameter(3, 4)
                    .setParameter(4, 5)
                    .list();
            for (Iterator iter=students.iterator(); iter.hasNext();) {
                Object[] obj = (Object[])iter.next();
                System.out.println(obj[0] + ", " + obj[1]);
            }

//采用 :参数名 方式，查询学号为1,2,3,4,5的学生
            List students = session.createQuery("select s.id, s.name from Student s where s.id in(:ids)")
                    .setParameterList("ids", new Object[]{1, 2, 3, 4, 5})
                    .list();
            for (Iterator iter=students.iterator(); iter.hasNext();) {
                Object[] obj = (Object[])iter.next();
                System.out.println(obj[0] + ", " + obj[1]);
            }

//查询2009-08的学生，可以调用mysql的日期格式化函数
            List students = session.createQuery("select s.id, s.name from Student s where date_format(s.createTime, '%Y-%m')=?")
                    .setParameter(0,  "2009-08")
                    .list();
            for (Iterator iter=students.iterator(); iter.hasNext();) {
                Object[] obj = (Object[])iter.next();
                System.out.println(obj[0] + ", " + obj[1]);
            }

SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
            //查询2009-08-01 到2009-08-20的学生，可以调用mysql的日期格式化函数
            List students = session.createQuery("select s.id, s.name from Student s where s.createTime between ? and ?")
                    .setParameter(0, sdf.parse("2009-08-01 00:00:00"))
                    .setParameter(1, sdf.parse("2009-08-20 23:59:59"))
                    .list();
            for (Iterator iter=students.iterator(); iter.hasNext();) {
                Object[] obj = (Object[])iter.next();
                System.out.println(obj[0] + ", " + obj[1]);
            }