常用HQL(Hibernate Query Language)查询

时间:2022-03-03 08:34:49

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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@Test
public 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]);
}