Mybatis动态插入数据（使用trim标签）

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>


    &lt;trim prefix=<span class="hljs-string">"values ("</span> suffix=<span class="hljs-string">")"</span> suffixOverrides=<span class="hljs-string">","</span> &gt;</br>
      #{id, jdbcType=VARCHAR},</br>
      #{memberId, jdbcType=VARCHAR},</br>
      &lt;<span class="hljs-keyword">if</span> test='messageClassify != <span class="hljs-keyword">null</span> <span class="hljs-keyword">and</span> messageClassify != <span class="hljs-string">""</span> '&gt;</br>
        #{messageClassify, jdbcType=VARCHAR},</br>
      &lt;/<span class="hljs-keyword">if</span>&gt;</br>
      &lt;<span class="hljs-keyword">if</span> test='messageCode != <span class="hljs-keyword">null</span> <span class="hljs-keyword">and</span> messageCode != <span class="hljs-string">""</span> '&gt;</br>
        #{messageCode, jdbcType=VARCHAR},</br>
      &lt;/<span class="hljs-keyword">if</span>&gt;</br>
      &lt;<span class="hljs-keyword">if</span> test='messageContent != <span class="hljs-keyword">null</span> <span class="hljs-keyword">and</span> messageContent != <span class="hljs-string">""</span> '&gt;</br>
        #{messageContent, jdbcType=VARCHAR},</br>
      &lt;/<span class="hljs-keyword">if</span>&gt;</br>
    &lt;/trim&gt;  </br>

</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。