查询一个对象（实体类必须有一个不带参数的构造方法）
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@Testpublic void test01() {
Session session = null;
try {
session = HibernateUtil.openSession();
/**
* 对于HQL而言，都是基于对象进行查询的
*/
Query query = session.createQuery("from Special");
List<Special> spes = query.list();
for(Special spe:spes) {
System.out.println(spe.getName());
}
} catch (Exception e) {
e.printStackTrace();
} finally {
HibernateUtil.close(session);
}
} |
使用select查询
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//不能使用select *进行查询//Query query = session.createQuery("select * from Special");/** * 可以使用链式查询的方式
*/
List<Special> spes = session.createQuery("select spe from Special spe").list();
for(Special spe:spes) {
System.out.println(spe.getName());
} |
条件查询
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List<Student> stus = session .createQuery("from Student where name like '%张%'")
.list();
for(Student stu:stus) {
System.out.println(stu.getName());
}-------------------------------------------------/** * 基于?的条件的查询
* 特别注意：jdbc设置参数的最小下标是1，hibernate是0
*/
List<Student> stus = session .createQuery("from Student where name like ?")
.setParameter(0, "%李%")
.list();
for(Student stu:stus) {
System.out.println(stu.getName());
}------------------------------------------------/** * 还可以基于别名进行查询，使用:xxx来说明别名的名称
*/
List<Student> stus = session .createQuery("from Student where name like :name and sex=:sex")
.setParameter("name", "%刘%")
.setParameter("sex", "男")
.list();
for(Student stu:stus) {
System.out.println(stu.getName());
} |
使用uniqueResult可以返回唯一的一个值/对象
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Long stus = (Long)session .createQuery("select count(*) from Student " +
"where name like :name and sex=:sex")
.setParameter("name", "%刘%")
.setParameter("sex", "男")
.uniqueResult();
System.out.println(stus);------------------------------------------------------Student stu = (Student)session .createQuery("select stu from Student stu where id=:id")
.setParameter("id", 1)
.uniqueResult();
System.out.println(stu.getName()); |
基于投影的查询，通过在列表中存储一个对象的数组
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List<Object[]> stus = session .createQuery("select stu.sex,count(*) from Student stu " +
"group by stu.sex")
.list();
for(Object[] obj:stus) {
System.out.println(obj[0]+":"+obj[1]);
} |
如果对象中相应的导航对象，可以直接导航完成查询
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List<Student> stus = session .createQuery("select stu from Student stu " +
"where stu.classroom.name=? and stu.name like ?")
.setParameter(0, "计算机教育班").setParameter(1, "%张%")
.list();
for(Student stu:stus) {
System.out.println(stu.getName());
} |
可以使用in来设置基于列表的查询，此处的查询需要使用别名进行查询
特别注意，使用in的查询必须在其他的查询之后
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List<Student> stus = session .createQuery("select stu from Student stu " +
"where stu.name like ? and stu.classroom.id in (:clas)")
.setParameter(0, "%张%")
.setParameterList("clas", new Integer[]{1,2})
.list();
for(Student stu:stus) {
System.out.println(stu.getName());
} |
使用setFirstResult和setMaxResult可以完成分页的offset和pageSize的设置
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List<Student> stus = session .createQuery("select stu from Student stu " +
"where stu.classroom.id in (:clas)")
.setParameterList("clas", new Integer[]{1,2})
.setFirstResult(0).setMaxResults(15)
.list();
for(Student stu:stus) {
System.out.println(stu.getName());
} |
可以通过is null来查询为空的对象,和sql一样不能使用=来查询null的对象
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List<Student> stus = session .createQuery("select stu from Student stu " +
"where stu.classroom is null")
.setFirstResult(0).setMaxResults(15)
.list();
for(Student stu:stus) {
System.out.println(stu.getName());
} |
连接查询
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/** * 使用对象的导航可以完成连接，但是是基于Cross JOIN，效率不高，
* 可以直接使用JOIN来完成连接
*/
List<Student> stus = session .createQuery("select stu from Student stu " +
"left join " +
"stu.classroom cla where cla.id=2")
.setFirstResult(0).setMaxResults(15)
.list();
for(Student stu:stus) {
System.out.println(stu.getName());
} |
统计班级学生的人数
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List<Object[]> stus = session .createQuery("select cla.name,count(stu.classroom.id) from Student stu " +
"right join stu.classroom cla group by cla.id")
.list();
for(Object[] stu:stus) {
System.out.println(stu[0]+","+stu[1]);
} |
把查询出来的数据封装成一个对象。
定义一个学生对象DTO
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package org.zttc.itat.model;
/** * DTO对象没有存储的意义，仅仅是用来进行数据的传输的
*
*/
public class StudentDto {
private int sid;
private String sname;
private String sex;
private String cname;
private String spename;
//省去set get方法
public StudentDto(int sid, String sname,
String sex, String cname,String spename) {
super();
this.sid = sid;
this.sname = sname;
this.sex = sex;
this.cname = cname;
this.spename = spename;
}
public StudentDto() {
}
} |
查询
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/** * 直接可以使用new XXObject完成查询，
* 注意，一定要加上Object的完整包名
* 这里使用的new XX，必须在对象中加入相应的构造函数
*/
List<StudentDto> stus = session .createQuery("select new org.zttc.itat.model.StudentDto" +
"(stu.id as sid,stu.name as sname,stu.sex as sex," +
"cla.name as cname,spe.name as spename) " +
"from Student stu left join stu.classroom cla " +
"left join cla.special spe")
.list();
for(StudentDto stu:stus) {
System.out.println(stu.getSid()+","+stu.getSname()+","+
stu.getSex()+","+stu.getCname()+","+stu.getSpename());
} |
having是为group来设置条件的
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List<Object[]> stus = session.createQuery("select spe.name," +
"(count(stu.classroom.special.id)) from Student stu right join " +
"stu.classroom.special spe group by spe " +
"having count(stu.classroom.special.id)>150")
.list();
for(Object[] obj:stus) {
System.out.println(obj[0]+":"+obj[1]);
} |