node.js - 使用 $group(aggregation) 返回多个对象

Question

我有一个与此类似的集合:

[
  {
    "_id":1,
    "name":"breakfast",
    "time":"10.00"
  },
  {
    "_id":3,
    "name":"lunch",
    "time":"12.07"
  },
  {
    "_id":2,
    "name":"breakfast",
    "time":"10.10"
  },
  {
    "_id":4,
    "name":"lunch",
    "time":"12.45"
  }
]

我想聚合成这样的东西:

{
  "breakfast":[
    {
      "_id":1,
      "name":"breakfast",
      "time":"10.00"
    },
    {
      "_id":2,
      "name":"breakfast",
      "time":"10.10"
    }
  ],
  "lunch":[
    {
      "_id":3,
      "name":"lunch",
      "time":"12.07"
    },
    {
      "_id":4,
      "name":"lunch",
      "time":"12.45"
    }
  ]
}                

我只能将它们分组，但无法根据膳食将主餐更改为早餐或午餐。名称(组名称)

$group: {
    _id: { meal: '$meal.name' },
    meals: { $push: '$meal' },
}

使用上面的代码我成功地产生了下面的输出。我唯一的挑战是将主要膳食更改为早餐或午餐，如上面在子组中所述。

{
  "meals":[
    {
      "_id":1,
      "name":"breakfast",
      "time":"10.00"
    },
    {
      "_id":2,
      "name":"breakfast",
      "time":"10.10"
    }
  ],
  "meals":[
    {
      "_id":3,
      "name":"lunch",
      "time":"12.07"
    },
    {
      "_id":4,
      "name":"lunch",
      "time":"12.45"
    }
  ]
}

Answer 1

在这里你可以得到答案。
在“分组”添加到数组后，您同样可以通过 "name" 分组键将所有内容 $push 到数组中，然后使用 $arrayToObject 将其转换为 $replaceRoot 中文档的键:

db.collection.aggregate([
  { "$group": {
    "_id": "$name",
    "data": { "$push": "$$ROOT" }
  }},
  { "$group": {
    "_id": null,
    "data": {
      "$push": {
        "k": "$_id",
        "v": "$data"
      }
    }
  }},
  { "$replaceRoot": {
    "newRoot": { "$arrayToObject": "$data" }
  }}
])

输出

[
  {
    "breakfast": [
      {
        "_id": 1,
        "name": "breakfast",
        "time": "10.00"
      },
      {
        "_id": 2,
        "name": "breakfast",
        "time": "10.10"
      }
    ],
    "lunch": [
      {
        "_id": 3,
        "name": "lunch",
        "time": "12.07"
      },
      {
        "_id": 4,
        "name": "lunch",
        "time": "12.45"
      }
    ]
  }
]

您可以在这个LINK中查看上述查询的结果