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.