Javascript 默认createdAt时间戳中的MongoDB Mongoose按日期分组

我有一个叫Session的模型。它具有id、设备和Mongoose默认时间戳。是这样的

{
    _id: 5da977e431e58d4e7fc1da1c,
    device: 'Galaxy M10',
    createdAt: 2019-10-18T08:29:24.498Z,
    updatedAt: 2019-10-18T08:32:10.768Z,

  }

我想按createdAt日期将此会话分组。所以我试过这个

const data = await db.Session.aggregate([
      { $match: { createdAt: { $gte: date } } },
      {
        $group: {
          _id: "$createdAt" ,
          count: { $sum: 1 }
        }
      }
    ]);

我得到的结果是

{ _id: 2019-10-17T11:32:49.346Z, count: 1 },
  { _id: 2019-10-18T07:14:45.695Z, count: 1 },
  { _id: 2019-10-17T10:49:35.434Z, count: 1 },
  { _id: 2019-10-18T08:17:05.999Z, count: 1 },
  { _id: 2019-10-17T09:56:53.574Z, count: 1 },
  { _id: 2019-10-18T07:14:15.154Z, count: 1 },
  { _id: 2019-10-18T07:07:19.346Z, count: 1 },
  { _id: 2019-10-18T07:13:57.720Z, count: 1 },
  { _id: 2019-10-17T13:09:17.721Z, count: 1 },
  { _id: 2019-10-18T07:31:59.900Z, count: 1 },
  { _id: 2019-10-18T08:29:24.498Z, count: 1 },
  { _id: 2019-10-18T08:05:54.339Z, count: 1 }

我的预期结果是

  { _id: 2019-10-18, count: 8 },
  { _id: 2019-10-17, count: 4 },

---

如果这是在SQL上，而不是在

groupbycreatedat

上，我会

groupbydate（createdAt）

。但是在MongoDB中我如何做到这一点呢？

您可以通过从日期中提取“dayOfMonth”、“month”和“year”并按三者进行分组来做到这一点。查询将变为：

db.Session.aggregate([
      { $match: { createdAt: { $gte: date } } },
      { $project: { dayOfMonth: { $dayOfMonth: $date },
                     month: { $month: $date },
                     year: { $year: $date },
     }
       },
      {
        $group: {
          _id: {    
               year: $year,
               month: $month,
               dayOfMonth: $dayOfMonth                
            } ,
          count: { $sum: 1 }
        }
      }
    ]);

---

它不起作用。错误是什么？这不是正确的答案，就像他询问输出一样…类似的…db.getCollection（'db'）。聚合（[{$match:{createdAt:{$gte:date}}，{$project:{yearMonthDayUTC:{$dateString:{format:'%Y-%m-%d'，date date:$createdAt:}}}，{$group:{id:“$yearMonthDayUTC”，计数：{$sum:1}}}]）；您是否找到了有效的解决方案？