Hibernate（4）hibernate的HQL详解
1 为什么需要学习HQL（hibernate query language）？
面向对象的查询语言，与SQL不同，HQL中的对象名是区分大小写的（除了Java类和属性，其他部分不区分大小写）；
HQL中查的是对象而不是表，并且支持多态；
HQL**主要通过Query来操作**Query q = session.createQuery(hql);
2 Hibernate HQL
Hibernate 工具类
http://blog.csdn.net/u013943420/article/details/70908878#t1使用的表结构和测试数据
create table student(
sid number primary key,
sname varchar2(45) not null,
ssex char(2) not null,
sdept varchar2(10) not null,
sage number(3),
saddress varchar2(45)
);
insert into student values(2004001, '林青霞', 'F', '计算机系', 22, '上海');
insert into student values(2004002, '刘德华', 'M', '外语系', 23, '南京');
insert into student values(2004003, '成龙', 'M', '化学系', 21, '山东');
insert into student values(2004004, '林可心', 'F', '计算机系', 22, '北京');
insert into student values(2004005, '周华健', 'M', '生物系', 24, '山东');
insert into student values(2004006, '周润发', 'M', '数学系', 20, '湖北');
create table course(
cid number primary key,
cname varchar2(50) not null,
ccredit number(3)
);
insert into course values(11, 'java编程', 6);
insert into course values(21, 'c++课程', 4);
insert into course values(31, 'oracle', 3);
insert into course values(41, 'javaEE', 100);
insert into course values(51, 'linux', 1);
create table studCourse(
stuCourseId number primary key,
sid number references student(sid),
cid number references course(cid),
grade number not null
);
insert into studCourse values(stucourse_seq.nextval, 2004001, 11, 90);
insert into studCourse values(stucourse_seq.nextval, 2004001, 21, 19);
insert into studCourse values(stucourse_seq.nextval, 2004003, 21, 45);
insert into studCourse values(stucourse_seq.nextval, 2004004, 41, 99);
insert into studCourse values(stucourse_seq.nextval, 2004006, 11, 39);
create sequence stucourse_seq
start with 1
increment by 1
minvalue 1
nomaxvalue
nocycle
nocache①数据库表映射
使用Hibernate工具，自动生成domain对象和映射文件，如果表有主外键的关系，则应当先映射主表，再映射从表。
②检索Student的全部属性
查询全部属性：from Student
查询部分属性：select sid, sname, saddress from Student
Session session = null;
Transaction ts = null;
try {
session = HibernateUtil.getCurrentSession();
ts = session.beginTransaction();
// 检索所有学生信息
List list = session.createQuery("from Student").list();
for(Student stu: list) {
System.out.println(stu.getSid() + " " + stu.getSname() + " " +
stu.getSaddress());
}
Iterator it = list.iterator();
while(it.hasNext()) {
System.out.println(it.next().getSid() + " " + it.next().getSname() + " " +
it.next().getSaddress());
}
ts.commit();
} catch (Exception e) {
e.printStackTrace();
if(ts!=null) {
ts.rollback();
}
throw new RuntimeException(e.getMessage());
} finally {
if(session!=null && session.isOpen()) {
session.close();
}
} ③检索Student的部分属性
检索学生的部分属性信息（Hibernate建议我们把整个对象的所有属性都查询出来）
// 核心代码
List list = session.createQuery("select sid, sname, saddress from Student").list();
for(int i=0; i<list.size(); i++) {
Object objs[] = (Object[]) list.get(i);
System.out.println(objs[0].toString() + " " + objs[1].toString() + " " +
objs[2].toString());
}
//------------------当查询只返回一列数据时----------
List list = session.createQuery("select count(*) from Student group by sdept").list();
// list中放置的是一个对象，而不是对象数组
for(int i=0; i<list.size(); i++) {
Object objs = list.get(i);
System.out.println(objs);
}④uniqueResult
uniqueResult:返回结果顶多有一个对象时，可以使用*uniqueResult()得到结果；但是，如果结果是多条，使用该方法就会抛出异常。*
Student stu = (Student) session.createQuery("from Student where sid='2004003'").uniqueResult();
if(stu!=null) {
System.out.println(stu.getSid() + " " + stu.getSname() + " " + stu.getSaddress());
}⑤过滤重复值distinct 及 between…and 和 in 与 not in的使用
// distinct
List list = session.createQuery("select distinct sage, ssex from Student").list();
// between...and
List list = session.createQuery("select distinct sage, ssex from Student where sage between 20 and 22").list();
// in 和 not in
List list = session.createQuery("select sage, ssex, sname from Student where sdept in ('计算机系', '外语系')").list();
for(int i=0; i<list.size(); i++) {
Object objs[] = (Object[]) list.get(i);
System.out.println(objs[0].toString() + " " + objs[1].toString());
}⑥分组查询group by 与 order by 及 having
List list = session.createQuery("select avg(sage), sdept from Student group by sdept").list();
List list = session.createQuery("select count(*), sdept from Student group by sdept having count(*) > 1").list();
// 女生多于1人的系
List list = session.createQuery("select count(*), sdept from Student where ssex='F' group by sdept having count(*) > 1").list(); ⑦其他常用查询
查询选修11号课程的最低分和最高分
List list = session.createQuery("select 11, max(grade), min(grade) from Studcourse where course.cid = 11").list();
for(int i=0; i
Object objs[] = (Object[]) list.get(i);
System.out.println(objs[0].toString() + " " + objs[1].toString() + " " +
objs[2].toString());
} 显示各科考试不及格学生的姓名，科目和分数
List list = session.createQuery("select student.sname, course.cname, grade from Studcourse where grade < 60").list();
for(int i=0; i
Object objs[] = (Object[]) list.get(i);
System.out.println(objs[0].toString() + " " + objs[1].toString() + " " +
objs[2].toString());
} 显示各个科目不及格学生数量
List list = session.createQuery("select course.cname, count(*) from Studcourse where grade < 60 group by course.cname").list();
for(int i=0; i
Object objs[] = (Object[]) list.get(i);
System.out.println(objs[0].toString() + " " + objs[1].toString());
} ⑧分页查询
setFirstResult(i) 从第几个开始取
setMaxResults(j) 最多取出多少个
按照年龄从小到大取出1~3个学生
List list = session.createQuery("from Student order by sage").setFirstResult(2).setMaxResults(3).list();
for(Student stu: list) {
System.out.println(stu.getSid() + " " + stu.getSname() + " " +
stu.getSage());
} 分页显示所有学生信息
private static void showResultByPage(int pageSize) {
// 设置分页变量
int pageNow = 1;
int pageCount = 1;
int rowCount = 1;
Session session = null;
Transaction ts = null;
try {
session = HibernateUtil.getCurrentSession();
ts = session.beginTransaction();
rowCount = Integer.parseInt(session.createQuery("select count(*) from Student").uniqueResult().toString());
pageCount = (rowCount - 1)/pageSize + 1;
for(int i=1; i<=pageCount; i++) {
System.out.println("******第"+i+"页**********");
List list = session.createQuery("from Student").setFirstResult((i-1)*pageSize).setMaxResults(pageSize).list();
for(Student stu: list) {
System.out.println(stu.getSid() + " " + stu.getSname() + " " +
stu.getSage());
}
}
ts.commit();
} catch (Exception e) {
e.printStackTrace();
if(ts!=null) {
ts.rollback();
}
throw new RuntimeException(e.getMessage());
} finally {
if(session!=null && session.isOpen()) {
session.close();
}
}
} ⑨参数绑定
setParameter();
使用参数绑定：
- 可读性好
- 性能提高
- 防止sql注入
参数绑定有两种形式：
？ ：这种方式使用位置绑定；
:xxx：这种方式采用参数名绑定；
如果两种方式同时使用，参数名绑定只能放在位置绑定之后
List list = session.createQuery("from Student where sage>? and saddress=:address")
.setString(0, "20")
.setString("address", "山东").list();
for(Student stu: list) {
System.out.println(stu.getSid() + " " + stu.getSname() + " " +
stu.getSage());
} ⑩ 在映射文件中得到hql语句
可以从映射文件中得到hql，执行查询语句，这样可以更加灵活，在某些情况下，可以考虑使用：比如在Student.hbm.xml中配置：
name="myquerytest">
from Student where sage>26
使用方式：
List list = session.getNamedQuery("myquerytest").list(); ⑪子查询、多表查询
⑫Criteria 使用
Session session = HibernateUtil.getCurrentSession();
Criteria cri = session.createCriteria(Student.class);
cri.add(Restrictions.gt("sage", (Integer)10));
List list = cri.list();
for(Student stu: list) {
System.out.println(stu.getSname() + " " + stu.getSage()+ " " +
stu.getSaddress());
} 3 Hibernate工具类扩展
public final class HibernateUtil {
private static SessionFactory sessionFactory = null;
// 线程局部模式
private static ThreadLocal threadLoacal = new ThreadLocal();
private HibernateUtil() {}
static {
sessionFactory = new Configuration().configure().buildSessionFactory();
}
// 获取全新的session
public static Session openSession() {
return sessionFactory.openSession();
}
// 获取和线程关联的session
public static Session getCurrentSession() {
Session session = threadLoacal.get();
// 判断是否得到
if(session==null) {
session = sessionFactory.openSession();
// 将session放入threadLocal
threadLoacal.set(session);
}
return session;
}
/// 分页
public static List executeQueryByPage(String hql, String[] paras, int pageSize, int pageNow) {
Session session = null;
List list = null;
try {
session = openSession();
Query query = session.createQuery(hql);
if(paras!=null && paras.length>0) {
for(int i=0; i///
query.setFirstResult((pageNow-1)*pageSize).setMaxResults(pageSize);
list = query.list();
} catch (Exception e) {
e.printStackTrace();
throw new RuntimeException(e.getMessage());
} finally {
if(session!=null && session.isOpen()) {
session.close();
}
}
return list;
}
/// 查询接口
public static List executeQuery(String hql, String[] paras) {
Session session = null;
List list = null;
try {
session = openSession();
Query query = session.createQuery(hql);
if(paras!=null && paras.length>0) {
for(int i=0; icatch (Exception e) {
e.printStackTrace();
throw new RuntimeException(e.getMessage());
} finally {
if(session!=null && session.isOpen()) {
session.close();
}
}
return list;
}
/// 修改和删除 批量sql
public static void executeUpdate(String hql, String[] paras) {
Session session = null;
Transaction ts = null;
try {
session = openSession();
ts = session.beginTransaction();
Query query = session.createQuery(hql);
if(paras!=null && paras.length>0) {
for(int i=0; icatch (Exception e) {
if(ts!=null) {
ts.rollback();
}
e.printStackTrace();
throw new RuntimeException(e.getMessage());
} finally {
if(session!=null && session.isOpen()) {
session.close();
}
}
}
// 添加
public static void save(Object obj) {
Session session = null;
Transaction ts = null;
try {
session = openSession();
ts = session.beginTransaction();
session.save(obj);
ts.commit();
} catch (Exception e) {
if(ts!=null) {
ts.rollback();
}
e.printStackTrace();
throw new RuntimeException(e.getMessage());
} finally {
if(session!=null && session.isOpen()) {
session.close();
}
}
}
}