如何使用组过滤mongo db中的数据？

Question

我正在尝试使用$group对数据进行$group ，但没有得到预期的输出。 这是我的代码https://codesandbox.io/s/lively-tree-hd0fo

app.get("/filter", async (req, res) => {
  try {
    BlogPostModel.aggregate([
      {
        $group: {
          _id: { empid: "$empid" },
          data: {
            $addToSet: { attendence: "$attendence", date: "$date", id: "$id" }
          }
        }
      }
    ]).then(function(re) {
      console.log(re); // [ { maxBalance: 98000 } ]
      res.send(re);
    });
  } catch (error) {
    console.log(error);
  }
});

得到输出

[
    {
        "_id": {
            "empid": "a2"
        },
        "data": [
            {
                "attendence": "P",
                "date": "2019-07-02T00:00:00.000Z",
                "id": "ec8d2107f1ec9c509845232f5aeeadd4"
            },
            {
                "attendence": "A",
                "date": "2019-07-01T00:00:00.000Z",
                "id": "c91a157c038328d0a9a9d501b2322ee4"
            }
        ]
    },
    {
        "_id": {
            "empid": "a1"
        },
        "data": [
            {
                "attendence": "A",
                "date": "2019-07-03T00:00:00.000Z",
                "id": "e85904145b5c104f108a701ab4a7d511"
            },
            {
                "attendence": "P",
                "date": "2019-07-02T00:00:00.000Z",
                "id": "75f8f4bd1db70519d90e740a89d5b77d"
            },
            {
                "attendence": "P",
                "date": "2019-07-01T00:00:00.000Z",
                "id": "a1e428379285f56c021f4792e74ed520"
            }
        ]
    }
]

预期产量

[
    {
        "empid": "a2",
        "name": "rajat",
        "data": [
            {
                "attendence": "P",
                "date": "2019-07-02T00:00:00.000Z",
                "id": "ec8d2107f1ec9c509845232f5aeeadd4"
            },
            {
                "attendence": "A",
                "date": "2019-07-01T00:00:00.000Z",
                "id": "c91a157c038328d0a9a9d501b2322ee4"
            }
        ]
    },
    {
        "empid": "a1",
        name:"ravi",
        "data": [
            {
                "attendence": "A",
                "date": "2019-07-03T00:00:00.000Z",
                "id": "e85904145b5c104f108a701ab4a7d511"
            },
            {
                "attendence": "P",
                "date": "2019-07-02T00:00:00.000Z",
                "id": "75f8f4bd1db70519d90e740a89d5b77d"
            },
            {
                "attendence": "P",
                "date": "2019-07-01T00:00:00.000Z",
                "id": "a1e428379285f56c021f4792e74ed520"
            }
        ]
    }
]

Answer 1

    BlogPostModel.aggregate(
  [
    {$group: {_id: '$empid', data: {$addToSet: { attendence: "$attendence", date: "$date", id: "$id" }}}}, 
    {$project: {empid: '$_id', _id: 0, data: 1}}
  ])