有时我们控制同一张表，但传入的参数不固定，操作表的字段不固定，就要用到mybatis动态插入。.xml如下：
<insert id="insertMessage" parameterType="com.sf.ccsp.member.client.request.MessageReq"> insert cx_customer_message (ID,MEMBERID, <if test='messageClassify != null and messageClassify != "" '> MESSAGEE_CLASSIFY, </if> <if test='messageCode != null and messageCode != "" '> MESSAGE_CODE, </if> <if test='messageContent != null and messageContent != "" '> MESSAGE_CONTENT </if> ) values ( #{id, jdbcType=VARCHAR}, #{memberId, jdbcType=VARCHAR}, <if test='messageClassify != null and messageClassify != "" '> #{messageClassify, jdbcType=VARCHAR}, </if> <if test='messageCode != null and messageCode != "" '> #{messageCode, jdbcType=VARCHAR}, </if> <if test='messageContent != null and messageContent != "" '> #{messageContent, jdbcType=VARCHAR} </if> ) </insert>问题来了，当messageClassify ！=null，但messageCode 和messageContent 为空时，会多出来逗号，以至于mybatis报错。正确的用法如下.xml：
<insert id="insertMessage" parameterType="com.sf.ccsp.member.client.request.MessageReq"> insert cx_customer_message <trim prefix="(" suffix=")" suffixOverrides="," > ID,MEMBERID, <if test='messageClassify != null and messageClassify != "" '> MESSAGEE_CLASSIFY, </if> <if test='messageCode != null and messageCode != "" '> MESSAGE_CODE, </if> <if test='messageContent != null and messageContent != "" '> MESSAGE_CONTENT, </if> </trim> <trim prefix="values (" suffix=")" suffixOverrides="," > #{id, jdbcType=VARCHAR}, #{memberId, jdbcType=VARCHAR}, <if test='messageClassify != null and messageClassify != "" '> #{messageClassify, jdbcType=VARCHAR}, </if> <if test='messageCode != null and messageCode != "" '> #{messageCode, jdbcType=VARCHAR}, </if> <if test='messageContent != null and messageContent != "" '> #{messageContent, jdbcType=VARCHAR}, </if> </trim> </insert>trim标签的属性
prefix：前缀覆盖并增加其内容。也就是给中的sql语句加上前缀；suffix：后缀覆盖并增加其内容。给包裹的sql语句加上后缀；prefixOverrides：前缀判断的条件。取消指定的前缀，如where；suffixOverrides：后缀判断的条件。取消指定的后缀，如and | or.，逗号等。