mybatis更新学习笔记

import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;

import org.apache.ibatis.session.SqlSession;

import cn.itcast.javaee.mybatis.util.MybatisUtil;

/**
 * 持久层 
 * @author AdminTC
 */
public class StudentDao {
    /**
     * 有条件更新学生
     */
    public void dynaUpdate(Integer id,String name,Double sal) throws Exception{
        SqlSession sqlSession = null;
        try{
            sqlSession = MybatisUtil.getSqlSession();

            Map<String,Object> map = new HashMap<String, Object>();
            map.put("pid",id);
            map.put("pname",name);
            map.put("psal",sal);
            sqlSession.update("studentNamespace.dynaUpdate",map);
            sqlSession.commit();
        }catch(Exception e){
            e.printStackTrace();
            sqlSession.rollback();
            throw e;
        }finally{
            MybatisUtil.closeSqlSession();
        }
    }

    public static void main(String[] args) throws Exception{
        StudentDao dao = new StudentDao();
        //关注SQL的变化
        //dao.dynaUpdate(1,null,9000D);//update students set sal=? where id=?
        //dao.dynaUpdate(1,"笨笨",null);//update students set name=? where id=?
        dao.dynaUpdate(1,"笨笨",10000D);//update students set name=? and sal=? where id=?
    }
}

<?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="studentNamespace">   

    <resultMap type="cn.itcast.javaee.mybatis.app12.Student" id="studentMap">
        <id property="id" column="students_id"/>
        <result property="name" column="students_name"/>
        <result property="sal" column="students_sal"/>
    </resultMap>

    <!-- set标签自动判断哪个是最后一个字段，会自动去掉最后一个,号 -->
    <update id="dynaUpdate" parameterType="map">
        update students 
        <set>
            <if test="pname!=null">
                students_name = #{pname},
            </if>
            <if test="psal!=null">
                students_sal = #{psal},         
            </if>
        </set>
        where students_id = #{pid}
    </update>

</mapper>