云开发（学习笔记）聚合分组查询group()

按商品分类展示商品

return dbRes.match({
        shopID: event.shopId
      })
      .group({
        _id: {
          sortName: '$sortItem.sortName'
        },
        list: $.push({
          _id: '$_id',
          goodsName: '$goodsName',
          goodsDesc: '$goodsDesc',
          goodsPrice: '$goodsPrice',
          imgUrl: '$imgUrl'
        })
      })
      .end().then(res => {
        console.log(res);
        return res
      })