MyBatis动态添加—trim标签

做添加时，部分字段有值，没值的字段不添加，这就是动态添加，使用 trim 标签就可以实现。

<insert id="insertSysUser" parameterType="com.mydemo.entity.SysUser">
        insert into sys_user
        <trim prefix="(" suffix=")" suffixOverrides=",">
            <if test="id != null and id != ''">
                id,
            </if>
            <if test="username != null and username != ''">
                username,
            </if>
            <if test="realName != null and realName != ''">
                real_name,
            </if>
            <if test="idcard != null and idcard != ''">
                idcard,
            </if>
            create_time
        </trim>
        <trim prefix="values(" suffix=")" suffixOverrides=",">
               <if test="id != null and id != ''">
                #{id, jdbcType = VARCHAR},
            </if>
            <if test="username != null and username != ''">
                #{username, jdbcType = VARCHAR},
            </if>
            <if test="realName != null and realName != ''">
                #{realName, jdbcType = VARCHAR},
            </if>
            <if test="idcard != null and idcard != ''">
                #{idcard, jdbcType = VARCHAR},
            </if>
            now()
        </trim>
    </insert>

最终结果：insert into sys_user ( id, username, real_name, idcard, create_time ) values( ?, ?, ?, ?, now() ) 

trim标签属性含义：

属性	描述
prefix	给sql语句拼接的前缀
suffix	给sql语句拼接的后缀
prefixesToOverride	去除sql语句前面的关键字或者字符，该关键字或者字符由prefixesToOverride属性指定，假设该属性指定为”AND”，当sql语句的开头为”AND”，trim标签将会去除该”AND”
suffixesToOverride	去除sql语句后面的关键字或者字符，该关键字或者字符由suffixesToOverride属性指定