对象DO与数据库字段间的映射

<resultMap id="UserResult" type="UserDO">
<result property="id" column="id" jdbcType="BIGINT"/>
<result property="gmtCreate" column="gmt_create" jdbcType="TIMESTAMP"/>
<result property="gmtModified" column="gmt_modified" jdbcType="TIMESTAMP"/>
<result property="userName" column="user_name" jdbcType="VARCHAR"/>
<result property="deleted" column="deleted" jdbcType="DECIMAL"/>
</resultMap>
2、定义sql语句字段模版
字符类型判断null和' '，其他类型只判null

Integer，Long之类的类型传0，如果是id要加判断''或者判断是否等于0,这样对于0值，会直接跳过判断语句

如果是状态类型的数值，只要判null，不然会过滤掉0这个条件判断
    <sql id="baseColumns">
    //sql语句前置DO对象字段模版
    gmt_create,
    gmt_modified,
    user_name,
    deleted
<sql id="insertColumns">
  //插入sql语句后置传入对象模版
    #{id},
    now(),
    now(),
    #{userName},
    #{deleted}
<sql id="batchInsertColumns">
      /批量插入sql语句后置传入对象模版，配合foreach使用
    #{item.id},
    now(),
now(),
    #{item.userName},
    #{item.deleted}
<!--动态更新列-->
<sql id="updateColumns">
  //sql语句更新列模版
    <if test="userName != null and userName != ''">,
        user_name = #{userName},
  <if test="deleted != null">,
        deleted = #{deleted}
<!--批量动态更新列-->
<sql id="batchUpdateColumns">
  //sql语句批量更新列模版
    <if test="item.userName != null and item.userName != ''">,
        user_name = #{item.userName}
<sql id="whereParam">
  //sql语句查询条件模版
    <where>
        <if test="id != null and id != ''">
          //基础模版
            AND id = #{id}
        <if test="start != null">
          //日期格式模版
            <![CDATA[
            AND  gmt_create >= #{start} ]]>
        <if test="end != null">
          // <![CDATA[]]> 不让xml编译内部语句
            <![CDATA[
            AND  gmt_create <= #{end} ]]>
        <if test="userName != null and userName != ''">
          //模糊查询模版
            AND user_name like CONCAT('%',#{userName},'%')
       <if test="userName != null and userName != ''">
          //模糊查询使用bind标签 https://www.cnblogs.com/youmingDDD/p/9435422.html
          <bind name="userNameLike" value=" '%' + userName + '%' "/>
            and user_name like  #{userNameLike}
    </where>
//基础实例
<insert id="insert" parameterType="UserDO">
    insert into sx_user (<include refid="baseColumns"/>)
    values (<include refid="insertColumns"/>)
</insert>
<insert id="batchInsert" parameterType="java.util.List">
    INSERT INTO sx_user (<include refid="baseColumns"/>)
    VALUES
    <foreach collection="list" item="item" index="index" separator=",">
        (<include refid="batchInsertColumns"/>)
    </foreach>
</insert>
<update id="updateById" parameterType="UserDO">
    update sx_user set gmt_modified=now(),
    <include refid="updateColumns"/>
    where id = #{id}
</update>
<update id="batchUpdateById" parameterType="java.util.List">
    <foreach collection="list" item="item" index="index" open="" close="" separator=";">
        update sx_user set gmt_modified=now(),
        <include refid="batchUpdateColumns"/>
        where id = #{item.id}
    </foreach>
</update>
<select id="countPageByCondition" parameterType="QueryCondition" resultType="java.lang.Long">
    SELECT COUNT(*)
    FROM sx_user
    <include refid="whereParam"/>
</select>
<select id="selectList" resultMap="UserResult">
    select
    <include refid="baseColumns"/>
    from sx_user
    where id = #{id}
</select>
<select id="listByIds" resultMap="UserResult">
    select
    <include refid="baseColumns"/>
    from sx_user
    where id IN
    <foreach item="item" index="index" collection="array" open="(" separator="," close=")">
      //in中多个参数拼接
        <!-- 如果直接传String ids (case:1,2,3,4) 
            <foreach collection="ids .split(',')" item="id" open="(" separator="," close=")">
            #{id}
        </foreach>
        #{item}
    </foreach>
</select>
<delete id="deleteById">
    delete from sx_user  where id = #{id}
</delete>
参考学习：https://blog.csdn.net/lu1024188315/article/details/78758943

    update table
    <trim prefix="set" suffixOverrides=",">
        <trim prefix="user_name = case" suffix="end,">
            <foreach collection="list" item="item" index="index">
                <if test="item.userName!=null">
                    when id=#{item.id} then #{item.userName}
            </foreach>
        </trim>
        <trim prefix="phone = case" suffix="end,">
            <foreach collection="list" item="item" index="index">
                when id=#{item.id} then ''
            </foreach>
        </trim>
        <trim prefix="num = case" suffix="end,">
            <foreach collection="list" item="item" index="index">
                when id=#{item.id} then null
            </foreach>
        </trim>
    </trim>
    where
    <foreach collection="list" separator="or" item="item" index="index">
        id=#{item.id}
    </foreach>
</update>