MyBatis 如何使用set标签呢？

set标签的功能简介

set标签主要用于结合update语句动态更新列信息，
使用set标签可避免条件末尾多余的逗号

例 使用 id 修改名称或备注
UserInfoMapper.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.java265.mapper.UserInfoMapper">
    <select id="selectUserInfo" resultType="com.java265.po.UserInfo">
        SELECT id,name,notes FROM UserInfo
        <where>
            <if test="id!=null and id!=''">
                id=#{id}
            </if>
        </where>
    </select>
    <!--使用set元素动态修改一个网站记录 -->
    <update id="updateUserInfo"
        parameterType="com.java265.po.UserInfo">
        UPDATE UserInfo
        <set>
            <if test="name!=null">name=#{name}</if>
            <if test="notes!=null">notes=#{notes}</if>
        </set>
        WHERE id=#{id}
    </update>
</mapper>

UserInfoMapper 类

package com.java265.mapper;
import java.util.list;
import org.apache.ibatis.annotations.Param;
import com.java265.po.UserInfo;
public interface UserInfoMapper {
    public List<UserInfo> selectUserInfo(UserInfo site);
   
    public int updateUserInfo(UserInfo site);
}

测试类

package com.java265.test;
import java.io.IOException;
import java.io.InputStream;
import java.util.List;
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 com.java265.mapper.UserInfoMapper;
import com.java265.po.UserInfo;
public class Test {
    public static void main(String[] args) throws IOException {
        InputStream config = Resources.getResourceAsStream("mybatis-config.xml");
        SqlSessionFactory ssf = new SqlSessionFactoryBuilder().build(config);
        SqlSession ss = ssf.openSession();
        UserInfo userInfo = new UserInfo();
        userInfo.setId(1);
        userInfo.setNotes("java爱好者");
        // 执行update语句前
        List<UserInfo> userList = ss.getMapper(UserInfoMapper.class).selectUserInfo(userInfo);
        for (UserInfo t : userList) {
            System.out.println(t);
        }
        int num = ss.getMapper(UserInfoMapper.class).updateUserInfo(userInfo);
        System.out.println("影响数据库行数" + num);
        // 执行update语句后
        List<UserInfo> userList2 = ss.getMapper(UserInfoMapper.class).selectUserInfo(userInfo);
        for (UserInfo t : userList2) {
            System.out.println(t);
        }
        ss.commit();
        ss.close();
    }
}

输出结果
DEBUG [main] - ==> Preparing: SELECT * FROM UserInfo WHERE id=?
DEBUG [main] - ==> Parameters: 1(Integer)
DEBUG [main] - <== Total: 1
UserInfo[id=1,name=王二,notes=java爱好者]
DEBUG [main] - ==> Preparing: UPDATE UserInfo SET notes=? where id=?
DEBUG [main] - ==> Parameters: java爱好者(String), 1(Integer)
DEBUG [main] - <== Updates: 1
影响数据库行数1
DEBUG [main] - ==> Preparing: SELECT * FROM UserInfo WHERE id=?
DEBUG [main] - ==> Parameters: 1(Integer)
DEBUG [main] - <== Total: 1
UserInfo[id=1,name=王二,notes=java爱好者]