Hibernate中的Criteria查询

第一、前言 阅读本篇文章之前，请先阅读：Hibernate中的HQL查询 第二、QBC简介 QBC：Query By Criteria,它是一种更加面向对象的查询方式，它把生成语句的过程全都融入到方法之中了。效率比HQL低。 第三、代码演示 1、基本查询

package com.demo; import java.util.List; import org.hibernate.Criteria; import org.hibernate.Session; import org.hibernate.Transaction; import com.demo.dto.Teacher; import com.demo.util.HibernateUtil; /** * 测试类 * @author shixiangcheng * 2020-07-04 */ public class Test { public static void main(String[] args) { Session s=HibernateUtil.getCurrentSession(); Transaction tx=s.beginTransaction(); //1.获取Criteria对象 Criteria c=s.createCriteria(Teacher.class); //2.获取结果 List<Teacher> list=c.list(); for(Teacher t:list) { System.out.println(t); } tx.commit(); } }

运行结果

Hibernate: select this_.id as id1_0_0_,this_.name as name2_0_0_ from t_teacher this_ [id=1,name=王一] [id=2,name=王二] [id=3,name=王三] [id=4,name=王四] [id=5,name=王五] [id=6,name=王六] [id=7,name=王七]

2、条件查询

//1.获取Criteria对象 Criteria c=s.createCriteria(Teacher.class); c.add(Restrictions.eq("id", 5));

运行结果

Hibernate: select this_.id as id1_0_0_,this_.name as name2_0_0_ from t_teacher this_ where this_.id=? [id=5,name=王五]

3、排序分页和统计查询 排序

//按id降序 c.addOrder(Order.desc("id")); //设置分页条件 c.setFirstResult(2);//设置查询的开始记录索引 c.setMaxResults(2);//设置每次查询的条数

运行结果

Hibernate: select this_.id as id1_0_0_,this_.name as name2_0_0_ from t_teacher this_ order by this_.id desc limit ?,? [id=5,name=王五] [id=4,name=王四]

统计

//1.获取Criteria对象 Criteria c=s.createCriteria(Teacher.class); //设置聚合函数 //c.setProjection(Projections.rowCount()); //按照某一字段统计 c.setProjection(Projections.count("id")); //2.获取结果 Long count=(Long)c.uniqueResult(); System.out.println(count);

运行结果

Hibernate: select count(this_.id) as y0_ from t_teacher this_ 7

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