1.映射

<!--app返回结果封装-->
<resultMap id="AppMap" type="java.util.HashMap">
  <!--不加这个映射 返回无id-->
  <id column="id" jdbcType="BIGINT" property="id" />
  <collection property="childsList" column="id" select="getChildrenModues">
  </collection>
</resultMap>

2.sql

<select id="commentList" parameterType="java.lang.Long" resultMap="AppMap">
  SELECT a.`id` as id,a.`username` AS username,a.`create_time` AS createTime,a.`goods_rank` AS goodsRank, a.`content`,a.`imgs`
    FROM t_comment a
  WHERE a.goods_id=#{goodsId}
</select>

<select id="getChildrenModues" parameterType="java.lang.Long" resultType="java.util.HashMap">
  SELECT b.`id` as id,b.create_time AS createTime,b.`username` AS username,b.content AS content,b.imgs AS imgs
    FROM t_comment b
  WHERE b.p_id=#{pId}
</select>

3.结果

 "success":true,
    "data":[
        {
            "imgs":"/2018/06/22/d681967ec2b8464e99206642b11a340a.jpg",
            "createTime":"2018-06-25 01:56:52",
            "childsList":[
                {
                    "imgs":"b.jpg",
                    "createTime":"2018-06-22 03:09:29",
                    "id":2,
                    "content":"哪里不好",
                    "username":"商家"
                },
                {
                    "imgs":"c.jpg",
                    "createTime":"2018-06-22 03:09:30",
                    "id":3,
                    "content":"你看",
                    "username":"小明"
                },
                {
                    "imgs":"d.jpg",
                    "createTime":"2018-06-22 03:09:33",
                    "id":4,
                    "content":"哦",
                    "username":"商家"
                }
            ],
            "id":1,
            "goodsRank":5,
            "content":"商品不好",
            "username":"小明"
        },
        {
            "imgs":"/2018/06/22/d681967ec2b8464e99206642b11a340a2.jpg",
            "createTime":"2018-06-25 01:56:52",
            "childsList":[

            ],
            "id":40,
            "goodsRank":5,
            "content":"商品不好2",
            "username":"小明2"
        }
    ],
    "message":"success"
}