Hibernate中的Criteria查詢

第一、前言

閱讀本篇文章之前，請先閱讀：Hibernate中的HQL查詢

第二、QBC簡介

QBC：Query By Criteria,它是一種更加面向對象的查詢方式，它把生成語句的過程全都融入到方法之中了。效率比HQL低。

第三、代碼示範

1、基本查詢

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;
/**
 * 測試類
 * @author shixiangcheng
 * 2020-07-04
 */
public class Test {
	public static void main(String[] args) {
		Session s=HibernateUtil.getCurrentSession();
		Transaction tx=s.beginTransaction();
		//1.擷取Criteria對象
		Criteria c=s.createCriteria(Teacher.class);
		//2.擷取結果
		List<Teacher> list=c.list();
		for(Teacher t:list) {
			System.out.println(t);
		}
		tx.commit();
	}
}
           

運作結果

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、條件查詢

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

運作結果

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、排序分頁和統計查詢

排序

//按id降序
c.addOrder(Order.desc("id"));
//設定分頁條件
c.setFirstResult(2);//設定查詢的開始記錄索引
c.setMaxResults(2);//設定每次查詢的條數
           

運作結果

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]
           

統計

//1.擷取Criteria對象
Criteria c=s.createCriteria(Teacher.class);
//設定聚合函數
//c.setProjection(Projections.rowCount());
//按照某一字段統計
c.setProjection(Projections.count("id"));
//2.擷取結果
Long count=(Long)c.uniqueResult();
System.out.println(count);
           

運作結果

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

歡迎大家積極留言交流學習心得，點贊的人最美麗，謝謝