Session session = null; try { session = HibernateSessionFactory.getSessionFactory().getCurrentSession(); session.beginTransaction(); //FROM子句 //简单的查询,Employee为实体名而不是数据库中的表名(面向对象特性) //hql = "FROM Employee"; //hql = "FROM Employee AS e"; // 使用别名 //hql = "FROM Employee e"; // 使用别名,as关键字可省略 String hql = "FROM User"; Query query = session.createQuery(hql); List results = query.list(); System.out.println(results.size()); //WHERE子句 // 带上过滤条件的(可以使用别名) //hql = "FROM Employee WHERE id < 10"; //hql = "FROM Employee e WHERE e.id < 10"; //hql = "FROM Employee e WHERE e.id < 10 AND e.id > 5"; hql = "FROM Role r WHERE r.id = 1"; query = session.createQuery(hql); results = query.list(); if(results != null & results.size() > 0) System.out.println(((Role) results.get(0)).getRoleName()); //ORDER BY 子句 //带上排序条件的: //hql = "FROM Employee e WHERE e.id < 10 ORDER BY e.name"; //hql = "FROM Employee e WHERE e.id < 10 ORDER BY e.name DESC"; //hql = "FROM Employee e WHERE e.id < 10 ORDER BY e.name DESC, e.id ASC"; hql = "FROM Role r WHERE r.id > 0 " + "ORDER BY r.id DESC, r.roleName ASC "; query = session.createQuery(hql); results = query.list(); System.out.println(results.size()); //指定select子句(不可以使用select *) //hql = "SELECT e FROM Employee e"; // 相当于"FROM Employee e" //hql = "SELECT e.name FROM Employee e"; // 只查询一个列,返回的集合的元素类型就是这个属性的类型 //hql = "SELECT e.id, e.name FROM Employee e"; // 查询多个列,返回的集合的元素类型是Object数组 //hql = "SELECT new Employee(e.id, e.name) FROM Employee e"; // 可以使用new语法,指定把查询出的部分属性封装到对象中 hql = "SELECT u.userName FROM User u"; query = session.createQuery(hql); //分页查询 query.setFirstResult(0); query.setMaxResults(10); results = query.list(); for (Object obj : results) { String str = (String) obj; System.out.println(str); } //聚集函数:count(), max(), min(), avg(), sum() //hql = "SELECT COUNT(*) FROM Employee"; // 返回的结果是Long型的 //hql = "SELECT min(id) FROM Employee"; // 返回的结果是id属性的类型 //GROUP BY Having /** hql = "SELECT e.name, COUNT(e.id) FROM Employee e GROUP BY e.name"; hql = "SELECT e.name, COUNT(e.id) FROM Employee e GROUP BY e.name " + "HAVING count(e.id) > 1"; hql = "SELECT e.name, COUNT(e.id) FROM Employee e WHERE id < 9 " + "GROUP BY e.name HAVING count(e.id) > 1"; hql = "SELECT e.name, COUNT(e.id) FROM Employee e " + "WHERE e.id < 9 " + "GROUP BY e.name " + "HAVING count(e.id) > 1 " + "ORDER BY count(e.id) ASC"; hql = "SELECT e.name,COUNT(e.id) AS c FROM Employee e " + "WHERE e.id < 9 " + "GROUP BY e.name " + "HAVING count(e.id) > 1 " + // 在having子句中不能使用列别名 "ORDER BY c ASC"; // 在orderby子句中可以使用列别名 */ hql = "SELECT COUNT(*), u.userName FROM User u GROUP BY u.userName "; query = session.createQuery(hql); results = query.list(); Object[] arr = (Object[]) results.get(0); System.out.println(arr[0] + ", " + arr[1]); //连接查询 // HQL是面向对象的查询 //>> 内连接(inner关键字可以省略) //hql = "SELECT e.id, e.name, d.name FROM Employee e JOIN e.department d"; //hql = "SELECT e.id, e.name, d.name FROM Employee e INNER JOIN e.department d"; //>> 左外连接(outer关键字可以省略) //hql = "SELECT e.id, e.name, d.name FROM Employee e LEFT OUTER JOIN e.department d"; //>> 右外连接(outer关键字可以省略) //hql = "SELECT e.id, e.name, d.name FROM Employee e RIGHT JOIN e.department d"; //可以使用更方便的方法 //hql = "SELECT e.id, e.name, e.department.name FROM Employee e"; //查询时使用参数 // >> 方式一:使用'?'占位 /** hql = "FROM Employee e WHERE id BETWEEN ? AND ?"; List list = session.createQuery(hql) .setParameter(0, 5) // 设置参数,第1个参数的索引为0。 .setParameter(1, 15) .list(); // >> 方式二:使用变量名 hql = "FROM Employee e WHERE id BETWEEN :idMin AND :idMax"; List list = session.createQuery(hql) .setParameter("idMax", 15) .setParameter("idMin", 5) .list(); // 当参数是集合时,一定要使用setParameterList()设置参数值 hql = "FROM Employee e WHERE id IN (:ids)"; List list = session.createQuery(hql) .setParameterList("ids", new Object[] { 1, 2, 3, 5, 8, 100 }) .list(); */ //update与delete,不会通知Session缓存 /** // >> Update int result = session.createQuery( "UPDATE Employee e SET e.name = ? WHERE id > 15") .setParameter(0, "无名氏") .executeUpdate(); // 返回int型的结果,表示影响了多少行。 // >> Delete int result1 = session.createQuery( "DELETE FROM Employee e WHERE id > 15") .executeUpdate(); // 返回int型的结果,表示影响了多少行。 */ session.getTransaction().commit(); } catch(Exception e) { e.printStackTrace(); session.getTransaction().rollback(); } finally { HibernateSessionFactory.closeSession(); }
* HQL: Hibernate Query Language.
* 特点:
* >> 1,与SQL相似,SQL中的语法基本上都可以直接使用。
* >> 2,SQL查询的是表和表中的列;HQL查询的是对象与对象中的属性。
* >> 3,HQL的关键字不区分大小写,类名与属性名是区分大小写的。
* >> 4,SELECT可以省略.