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