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]);} |