MongoDB：就地分组嵌套数组的元素

想知道如何使用聚合管道将procedures个数组按type就地分组.

因此，将这个转变为:

[
    {
        "airport": "MSP",
        "country": "USA",
        "procedures": [
            {
                "name": "ABC1",
                "type": "DEP"
            },
            {
                "name": "JKL2",
                "type": "ARR"
            },
            {
                "name": "LMN3",
                "type": "DEP"
            },
            {
                "name": "PQR4",
                "type": "ARR"
            }
        ]
    },
    {
        "airport": "CMH",
        "country": "USA",
        "procedures": [
            {
                "name": "GHI4",
                "type": "ARR"
            },
            {
                "name": "RST3",
                "type": "ARR"
            },
            {
                "name": "TUV7",
                "type": "DEP"
            },
            {
                "name": "XYZ4",
                "type": "ARR"
            }
        ]
    }
]

进入这一阶段:

[
    {
        "airport": "MSP",
        "country": "USA",
        "procedures": {
            "ARR": [
                {
                    "name": "JKL2",
                    "type": "ARR"
                },
                {
                    "name": "PQR4",
                    "type": "ARR"
                }
            ],
            "DEP": [
                {
                    "name": "ABC1",
                    "type": "DEP"
                },
                {
                    "name": "LMN3",
                    "type": "DEP"
                },
            ]
        }
    },
    {
        "airport": "CMH",
        "country": "USA",
        "procedures": {
            "ARR": [
                {
                    "name": "GHI4",
                    "type": "ARR"
                },
                {
                    "name": "RST3",
                    "type": "ARR"
                },

                {
                    "name": "XYZ4",
                    "type": "ARR"
                }
            ],
            "DEP": [
                {
                    "name": "TUV7",
                    "type": "DEP"
                }
            ]
        }
    }
]

我已经走到了

db.collection.aggregate([
  {
    "$unwind": "$procedures"
  },
  {
    "$group": {
      _id: "$procedures.type",
      procedures: {
        $push: "$procedures"
      }
    }
  }
])

但它丢失了airport个 struct ，并将数据混合在一起:

[
  {
    "_id": "DEP",
    "procedures": [
      {
        "name": "ABC1",
        "type": "DEP"
      },
      {
        "name": "LMN3",
        "type": "DEP"
      },
      {
        "name": "TUV7",
        "type": "DEP"
      }
    ]
  },
  {
    "_id": "ARR",
    "procedures": [
      {
        "name": "JKL2",
        "type": "ARR"
      },
      {
        "name": "PQR4",
        "type": "ARR"
      },
      {
        "name": "GHI4",
        "type": "ARR"
      },
      {
        "name": "RST3",
        "type": "ARR"
      },
      {
        "name": "XYZ4",
        "type": "ARR"
      }
    ]
  }
]