ICode9

精准搜索请尝试: 精确搜索
首页 > 数据库> 文章详细

mybatis 10: 动态sql --- part2

2022-08-15 01:03:21  阅读:199  来源: 互联网

标签:10 users 批量 update --- part2 com id String


< foreach >标签

作用

  • 用来进行循环遍历,完成循环条件的查询,批量删除,批量增加,批量更新

用法

  • 包括循环查询 + 批量删除 + 批量增加 + 批量更新的用法

UsersMapper.java

package com.example.mapper;

import com.example.pojo.User;

import java.util.List;

/**
 * 数据访问层的接口,定义对数据库完成的CRUD的操作
 */
public interface UsersMapper {


    //循环查询
    List<User> getByIds(Integer []id_array);

    //批量删除
    int deleteByIds(Integer []id_array);

    //批量插入
    int insertBatch(List<User> users);
    
    //批量更新
    int updateBatch(List<User> users);
}

UsersMapper.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">

<mapper namespace="com.example.mapper.UsersMapper">

    <!--
        //循环查询
        List<User> getByIds(Integer []id_array);
    -->
    <select id="getByIds" resultType="user">
        select
            <include refid="allColumns"/>
        from
            users
        where
            id
        in
            <foreach collection="array" item="id" open="(" close=")" separator=",">
                #{id}
            </foreach>
    </select>


    <!--
        //批量删除
        int deleteByIds(Integer []id_array);
    -->
    <delete id="deleteByIds">
        delete from
                   users
        where
            id
        in
        <foreach collection="array" item="id" separator="," open="(" close=")">
            #{id}
        </foreach>
    </delete>
    
    
    <!--
        //批量插入
        int insertBatch(List<User> users);
    -->
    <insert id="insertBatch">
        insert into
            users(username, birthday, sex, address)
        values
            <foreach collection="list" item="user" separator=",">
                (#{user.userName}, #{user.birthday}, #{user.sex}, #{user.address})
            </foreach>
    </insert>
    
    
    <!--
        //批量更新
        int updateBatch(List<User> users);
        private Integer id;
        private String userName;
        private Date birthday;
        private String sex;
        private String address;
    -->
    <update id="updateBatch">
        <foreach collection="list" item="user" separator=";">
            update
                users
            <set>
                <if test="user.userName != null and user.userName != ''">
                    username=#{user.userName},
                </if>

                <if test="user.birthday != null">
                    birthday=#{user.birthday},
                </if>

                <if test="user.sex != null and user.sex != ''">
                    sex=#{user.sex},
                </if>

                <if test="user.address != null and user.address != ''">
                    address=#{user.address},
                </if>
            </set>
            where
                id=#{user.id}
        </foreach>
    </update>
</mapper>

映射文件分析

  • 当入参是数组时,parameterType可以不写,

    • 其实只有当入参类型是实体类时,才必须指明其类型,其他类型的数据皆可不写
  • < foreach >标签的属性说明

    • collection:指明待遍历的数据容器的类型,可选的有三个:array,list,map
    • item:给遍历出的每个元素指定一个名称,便于在标签内使用
    • open 和 close:原先sql语句,in后面待遍历的数据放在括号中,这里通过标签属性的形式来实现
      • 可以将sql语句和标签的书写分隔开,使得代码更加直观
      • 注意:这是循环外层的括号,用来容纳所有的元素,循环内部的元素自身的括号不能用这对标签,要手动加上
    • 是否要使用 open 和 close标签的说明:
  <!-- 批量删除时使用 --> 
  <foreach collection="array" item="id" separator="," open="(" close=")">
       #{id}
   </foreach>
  
  <!-- 批量插入时未使用 -->
   <foreach collection="list" item="user" separator=",">
       
       <!-- 为元素手动添加括号 -->
       (#{user.userName}, #{user.birthday}, #{user.sex}, #{user.address})		
   </foreach>
  
  
  <!-- 不同选择的依据:
  	看被遍历的元素是否要放在同一个括号内,需要则使用open 和 close标签,否则不用
  	元素自身需要括号,则手动添加
  -->
  • separator:遍历出的元素之间用什么符号分隔,mybatis框架会确保间隔符号的正确使用

    • 正确使用是指:在指定需要的间隔符后,间隔符号的个数以及出现在元素之间的位置,由mybatis自动正确放置(如果有多个元素的话)
  • 进行批量更新操作时

    • 本质:由底层解析出的sql语句可知,本质执行的是多条独立的update语句
      • 这也决定了< update >标签内应该是一个 < foreach >标签,分隔符应该是";",用来间隔多条相互独立的update语句
    • 注意:这与执行一条update语句,影响多行记录是不同的,必须在jdbc.properties文件中的url的值后新增配置:allowMultiQueries=true
  jdbc.driverClassName=com.mysql.cj.jdbc.Driver
  jdbc.url=jdbc:mysql://ip:3306/ssm?useUnicode=true&characterEncoding=utf8&allowMultiQueries=true
  jdbc.username=XXXX
  jdbc.password=YYYY
  • 不修改jdbc.properties时报错
    image

  • 各sql标签在底层分别被解析为

//批量查询

==>  Preparing: select id, username, birthday, sex, address from users where id in ( ? , ? , ? )
//批量删除

==>  Preparing: delete from users where id in ( ? , ? )
//批量插入

==>  Preparing: insert into users(username, birthday, sex, address) values (?, ?, ?, ?) , (?, ?, ?, ?) , (?, ?, ?, ?)
//批量更新

==>  Preparing: 
update users SET username=?, birthday=?, sex=?, address=? where id=? ;
update users SET username=?, birthday=?, sex=?, address=? where id=? ; 
update users SET username=?, birthday=?, sex=?, address=? where id=?

测试代码

package com.example.mapper;

import com.example.pojo.User;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;

import java.io.IOException;
import java.io.InputStream;
import java.lang.reflect.Array;

import java.util.List;


public class TestUsersMapper {

    //时间刷
    SimpleDateFormat date = new SimpleDateFormat("yyyy-MM-dd");

    //SqlSession对象
    SqlSession sqlSession;

    //mybatis动态代理对象
    UsersMapper usersMapper;

    //获取SqlSession
    @Before
    public void getSqlSession() throws IOException {
        //读取核心配置文件
        InputStream in = Resources.getResourceAsStream("SqlMapConfig.xml");
        //创建SqlSessionFactory对象
        SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(in);
        //获取SqlSession
        sqlSession = factory.openSession();
        //获取mybatis动态代理对象
        usersMapper = sqlSession.getMapper(UsersMapper.class);
    }

    //归还SqlSession
    @After
    public void closeSession(){
        sqlSession.close();
    }

    //循环查询测试
    @Test
    public void testGetByIds(){
        Integer []id_array = {1, 3, 5};
        List<User> users = usersMapper.getByIds(id_array);
        users.forEach(System.out::println);
    }

    //批量删除测试
    @Test
    public void testDeleteByIds(){
        Integer []id_array = {3, 29};
        int num = usersMapper.deleteByIds(id_array);
        if(num == 2){
            System.out.println("批量删除成功!");
            sqlSession.commit();
        }else{
            System.out.println("批量删除失败!");
        }
    }
    
    //批量插入测试
    @Test
    public void testInsertBatch() throws ParseException {
        User u1 = new User("西决", date.parse("2001-01-01"), "男", "北京");
        User u2 = new User("南音", date.parse("2002-02-02"), "女", "北京");
        User u3 = new User("北北", date.parse("2003-03-03"), "男", "北京");

        List<User> users = new ArrayList<>();
        users.add(u1);
        users.add(u2);
        users.add(u3);

        int num = usersMapper.insertBatch(users);
        if(num == 3){
            System.out.println("批量插入成功!");
            sqlSession.commit();
        }else{
            System.out.println("批量插入失败!");
        }
    }
    
    //批量更新测试
    @Test
    public void testUpdateBatch() throws ParseException {
        User u1 = new User(31,"西决2", date.parse("2001-01-01"), "男", "北京");
        User u2 = new User(32,"南音2", date.parse("2002-02-02"), "女", "北京");
        User u3 = new User(33,"北北2", date.parse("2003-03-03"), "男", "北京");

        List<User> users = new ArrayList<>();
        users.add(u1);
        users.add(u2);
        users.add(u3);

        int num = usersMapper.updateBatch(users);
        if(num == 1){
            System.out.println("批量更新成功!");
            sqlSession.commit();
        }else{
            System.out.println("批量更新失败!");
        }
    }
}

测试代码分析(着重分析一下批量更新)

  • 在执行批量更新操作时,为什么数据表的记录明明修改了3条,输出结果中更新结果的返回值却是1呢?
  • 更新后的数据表,修改了3条记录

image

  • 批量更新后的返回结果
<==    Updates: 1
批量更新成功!
  • 原因:

    • 首先要区别< update >标签和update语句:在 < update >标签中有一个< foreach >标签,他循环了3条相互独立的update语句
    • 注意:每条update语句恰巧都只是修改了一条记录,所以< update >标签返回3次1后结束,因为循环3次后循环标签结束了
    • 对于如下测试代码,num其实被赋值3次,num的值是最后一次赋值的结果,本次测试恰好是:1
      • 其实笔者不太确定num是否被赋值了3,但是根据底层输出的结果可知,起作用的一定是最后一条update语句影响的记录条数
      • 不是循环的3条update语句影响条数的和,因为输出结果:是1,而不是3
   int num = usersMapper.updateBatch(users);

输出结果

//批量查询结果

Checking to see if class com.example.mapper.TestUsersMapper matches criteria [is assignable to Object]
Checking to see if class com.example.mapper.UsersMapper matches criteria [is assignable to Object]
Opening JDBC Connection
Created connection 16148478.
Setting autocommit to false on JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@f667fe]
==>  Preparing: select id, username, birthday, sex, address from users where id in ( ? , ? , ? )
==> Parameters: 1(Integer), 3(Integer), 5(Integer)
<==    Columns: id, username, birthday, sex, address
<==        Row: 1, 荷包蛋, 2002-08-23, 女, 黑河市
<==        Row: 3, 小张, 1999-02-22, 1, 长沙
<==        Row: 5, 段, 2001-03-10, 1, 太原
<==      Total: 3
Users{id=1, userName='荷包蛋', birthday=Fri Aug 23 00:00:00 CST 2002, sex='女', address='黑河市'}
Users{id=3, userName='小张', birthday=Mon Feb 22 00:00:00 CST 1999, sex='1', address='长沙'}
Users{id=5, userName='段', birthday=Sat Mar 10 00:00:00 CST 2001, sex='1', address='太原'}
Resetting autocommit to true on JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@f667fe]
Closing JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@f667fe]
Returned connection 16148478 to pool.

Process finished with exit code 0
//批量删除结果

Checking to see if class com.example.mapper.TestUsersMapper matches criteria [is assignable to Object]
Checking to see if class com.example.mapper.UsersMapper matches criteria [is assignable to Object]
Opening JDBC Connection
Created connection 544966217.
Setting autocommit to false on JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@207b8649]
==>  Preparing: delete from users where id in ( ? , ? )
==> Parameters: 3(Integer), 29(Integer)
<==    Updates: 2
批量删除成功!
Committing JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@207b8649]
Resetting autocommit to true on JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@207b8649]
Closing JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@207b8649]
Returned connection 544966217 to pool.

Process finished with exit code 0
//批量增加结果

Checking to see if class com.example.mapper.TestUsersMapper matches criteria [is assignable to Object]
Checking to see if class com.example.mapper.UsersMapper matches criteria [is assignable to Object]
Opening JDBC Connection
Created connection 749604930.
Setting autocommit to false on JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@2cae1042]
==>  Preparing: insert into users(username, birthday, sex, address) values (?, ?, ?, ?) , (?, ?, ?, ?) , (?, ?, ?, ?)
==> Parameters: 西决(String), 2001-01-01 00:00:00.0(Timestamp), 男(String), 北京(String), 南音(String), 2002-02-02 00:00:00.0(Timestamp), 女(String), 北京(String), 北北(String), 2003-03-03 00:00:00.0(Timestamp), 男(String), 北京(String)
<==    Updates: 3
批量插入成功!
Committing JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@2cae1042]
Resetting autocommit to true on JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@2cae1042]
Closing JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@2cae1042]
Returned connection 749604930 to pool.

Process finished with exit code 0
//批量更新结果

Checking to see if class com.example.mapper.TestUsersMapper matches criteria [is assignable to Object]
Checking to see if class com.example.mapper.UsersMapper matches criteria [is assignable to Object]
Opening JDBC Connection
Created connection 1718322084.
Setting autocommit to false on JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@666b83a4]
==>  Preparing: update users SET username=?, birthday=?, sex=?, address=? where id=? ; update users SET username=?, birthday=?, sex=?, address=? where id=? ; update users SET username=?, birthday=?, sex=?, address=? where id=?
==> Parameters: 西决2(String), 2001-01-01 00:00:00.0(Timestamp), 男(String), 北京(String), 31(Integer), 南音2(String), 2002-02-02 00:00:00.0(Timestamp), 女(String), 北京(String), 32(Integer), 北北2(String), 2003-03-03 00:00:00.0(Timestamp), 男(String), 北京(String), 33(Integer)
<==    Updates: 1
批量更新成功!
Committing JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@666b83a4]
Resetting autocommit to true on JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@666b83a4]
Closing JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@666b83a4]
Returned connection 1718322084 to pool.

Process finished with exit code 0

标签:10,users,批量,update,---,part2,com,id,String
来源: https://www.cnblogs.com/nefu-wangxun/p/16586821.html

本站声明: 1. iCode9 技术分享网(下文简称本站)提供的所有内容,仅供技术学习、探讨和分享;
2. 关于本站的所有留言、评论、转载及引用,纯属内容发起人的个人观点,与本站观点和立场无关;
3. 关于本站的所有言论和文字,纯属内容发起人的个人观点,与本站观点和立场无关;
4. 本站文章均是网友提供,不完全保证技术分享内容的完整性、准确性、时效性、风险性和版权归属;如您发现该文章侵犯了您的权益,可联系我们第一时间进行删除;
5. 本站为非盈利性的个人网站,所有内容不会用来进行牟利,也不会利用任何形式的广告来间接获益,纯粹是为了广大技术爱好者提供技术内容和技术思想的分享性交流网站。

专注分享技术,共同学习,共同进步。侵权联系[81616952@qq.com]

Copyright (C)ICode9.com, All Rights Reserved.

ICode9版权所有