数据库中：device表的id_user列参照users表的主键id

    <resultMap type="User" id="userResultMap">
        <id column="id" property="id"/>
        <result column="tel" property="tel"/>
        <result column="num_fan" property="numFan"/>
        <result column="type" property="type"/>
        <result column="is_accept_faned" property="isAcceptFaned"/>
    </resultMap>

    <resultMap type="Device" id="deviceResultMap">
        <id column="id" property="id" />
        <result column="imei" property="imei" />
        <result column="imsi" property="imsi" />
        <result column="channel" property="channel" />
        <association column="id_user" property="user" select="queryUser"/>
    </resultMap>

    <select id="queryUser" resultMap="userResultMap">
        select * from users where id=#{id}
    </select>

在deviceResultMap中添加
<association column="id_user" property="user" select="queryUser"/>
意思是，在device表中查询id_user列，映射为user属性，在映射时通过queryUser查询，select * from users where id=#{id}这里的#{id}可以为任意字符串，#{xxx}，也是可以的。实际上执行的是

select * from users where id = id_user(此处为查询出来的id_user列的值)