Hibernate的几种查询方式 HQL,QBC,QBE,离线查询,复合查询,分页查询
HQL查询方式
这一种我最常用，也是最喜欢用的，因为它写起来灵活直观，而且与所熟悉的SQL的语法差不太多。条件查询、分页查询、连接查询、嵌套查询，写起来与SQL语法基本一致，唯一不同的就是把表名换成了类或者对象。其它的，包括一些查询函数（count(),sum()等）、查询条件的设定等，全都跟SQL语法一样。
示例：
1: Session session = SessionFactory.getCurrentSession();
2: User user = null;
3: Transaction ts = session.beginTransaction();
4: try {
5: Query query = session.createQuery("from User as u where name='ijse'");
6: user= (User) query.list().get(0);
7: session.commit();
8: } catch (HibernateException ex) {
9: ts.rollBack();
10: ex.printStackTrace();
11: }
12: System.out.println(user.getName());
QBC(Query By Criteria) 查询方式
这种方式比较面向对象方式，重点是有三个描述条件的对象：Restrictions,Order,Projections。使用QBC查询，一般需要以下三个步骤：
- 使用Session实例 的createCriteria()方法创建Criteria对象
- 使用工具类Restrictions的方法为Criteria对象设置查询条件，Order工具类的方法设置排序方式，Projections工具类的方法进行统计和分组。
- 使用Criteria对象的list()方法进行查询并返回结果
Restrictions类的常用方法：
方法名称 |
描述 |
| Restrictions.eq | 等于 |
| Restrictions.allEq | 使用Map,Key/Valu进行多个等于的比对 |
| Restrictions.gt | 大于 |
| Restrictions.ge | 大于等于 |
| Restrictions.lt | 小于 |
| Restrictions.le | 小于等于 |
| Restrictions.between | 对应SQL的between |
| Restrictions.like | 对应SQL的like |
| Restrictions.in | 对应SQL的in |
| Restrictions.and | and关系 |
| Restrictions.or | or关系 |
| Restrictions.sqlRestriction | SQL限定查询 |
Order类的常用方法：
方法名称 |
描述 |
| Order.asc | 升序 |
| Order.desc | 降序 |
Projections类的常用方法
方法名称 |
描述 |
| Projections.avg | 求平均值 |
| Projections.count | 统计某属性的数量 |
| Projections.countDistinct | 统计某属性不同值的数量 |
| Projections.groupProperty | 指定某个属性为分组属性 |
| Projections.max | 求最大值 |
| Projections.min | 求最小值 |
| Projections.projectionList | 创建一个ProjectionList对象 |
| Projections.rowCount | 查询结果集中的记录条数 |
| Projections.sum | 求某属性的合计 |
示例：
1: Session session = SessionFactory.getCurrentSession();
2: User user = null;
3: Transaction ts = session.beginTransaction();
4: try {
5: Criteria criteria = session.createCriteria(User.class);
6: criteria.add(Restrictions.eq("name","ijse"));
7: user= (User) criteria.list().get(0);
8: session.commit();
9: } catch (HibernateException ex) {
10: ts.rollBack();
11: ex.printStackTrace();
12: }
13: System.out.println(user.getName());
1: Session session = SessionFactory.getCurrentSession();
2: User user = null;
3: Transaction ts = session.beginTransaction();
4: try {
5: Criteria criteria = session.createCriteria(User.class);
6: criteria.add(Restrictions.eq("name","ijse"));
7: user= (User) criteria.list().get(0);
8: session.commit();
9: } catch (HibernateException ex) {
10: ts.rollBack();
11: ex.printStackTrace();
12: }
13: System.out.println(user.getName());
QBE（Query By Example）查询方式
将一个对象的非空属性作为查询条件进行查询。
示例：
1: Session session = SessionFactory.getCurrentSession();
2: User user = new User();
3: user.setName("ijse");
4: Transaction ts = session.beginTransaction();
5: try {
6: Criteria criteria = session.createCriteria(User.class);
7: criteria.add(Example.create(user));
8: user= (User) criteria.list().get(0);
9: session.commit();
10: } catch (HibernateException ex) {
11: ts.rollBack();
12: ex.printStackTrace();
13: }
14: System.out.println(user.getName());
1: Session session = SessionFactory.getCurrentSession();
2: User user = new User();
3: user.setName("ijse");
4: Transaction ts = session.beginTransaction();
5: try {
6: Criteria criteria = session.createCriteria(User.class);
7: criteria.add(Example.create(user));
8: user= (User) criteria.list().get(0);
9: session.commit();
10: } catch (HibernateException ex) {
11: ts.rollBack();
12: ex.printStackTrace();
13: }
14: System.out.println(user.getName());
离线查询
离线查询就是建立一个DetachedCriteria对象，将查询的条件等指定好，然后在session.beginTransaction()后将这个对象传入。通常这个对象可以在表示层建立，然后传入业务层进行查询。
示例：
1: DetachedCriteria detachedCriteria = DetachedCriteria.forClass(User.class);
2: detachedCriteria.add(Restrictions.eq("name","ijse");
3:
4: Session session = SessionFactory.getCurrentSession();
5: User user = new User();
6: Transaction ts = session.beginTransaction();
7: try {
8: Criteria criteria = detachedCriteria.getExecutableCriteria(session);
9: user= (User) criteria.list().get(0);
10: session.commit();
11: } catch (HibernateException ex) {
12: ts.rollBack();
13: ex.printStackTrace();
14: }
15: System.out.println(user.getName());
1: DetachedCriteria detachedCriteria = DetachedCriteria.forClass(User.class);
2: detachedCriteria.add(Restrictions.eq("name","ijse");
3:
4: Session session = SessionFactory.getCurrentSession();
5: User user = new User();
6: Transaction ts = session.beginTransaction();
7: try {
8: Criteria criteria = detachedCriteria.getExecutableCriteria(session);
9: user= (User) criteria.list().get(0);
10: session.commit();
11: } catch (HibernateException ex) {
12: ts.rollBack();
13: ex.printStackTrace();
14: }
15: System.out.println(user.getName());
复合查询
复合查询就是在原有查询的基础上再进行查询，可以调用Criteria对象的createCriteria()方法在这个Criteria对象的基础上再进行查询。
示例：
1: Session session = SessionFactory.getCurrentSession();
2: User user = new
3: User();
4: Transaction ts = session.beginTransaction();
5: try
6: {
7: Criteria criteria1 =
8: session.createCriteria(Room.class);
9: Criteria
10: criteria2 =criterial1.createCriteria("User");
11:
12: criteria2.add(Restrictions.eq("name",new String("ijse"));
13:
14: user= (User) criteria.list().get(0);
15:
16: session.commit();
17: } catch (HibernateException ex) {
18:
19: ts.rollBack();
20:
21: ex.printStackTrace();
22: }
23: System.out.println(user.getName());
分页查询
分页查询主要是要指定两个参数：从第几条数据开始，取多少条数据。可以通过调用Query或者Criteria对象的setFirstResult()和setMaxResults()方法分别进行设定。
示例：
1: Session session = SessionFactory.getCurrentSession();
2: List userList = null;
3: Transaction ts = session.beginTransaction();
4: try {
5: Criteria criteria = session.createCriteria(User.class);
6: criteria.setFirstResult(0);//从第一个数据开始
7: criteria.setMaxResults(10);//取10条记录
8: userList = (List) criterial.list();
9: session.commit();
10: } catch (HibernateException ex) {
11: ts.rollBack();
12: ex.printStackTrace();
13: }
1: Session session = SessionFactory.getCurrentSession();
2: List userList = null;
3: Transaction ts = session.beginTransaction();
4: try {
5: Criteria criteria = session.createCriteria(User.class);
6: criteria.setFirstResult(0);//从第一个数据开始
7: criteria.setMaxResults(10);//取10条记录
8: userList = (List) criterial.list();
9: session.commit();
10: } catch (HibernateException ex) {
11: ts.rollBack();
12: ex.printStackTrace();
13: }