mongodb数组聚合提取到父级

Question

我正在尝试从 mongodb 对象的内部数组中获取第一个日期，并将其添加到它的父级聚合中。示例：

car: {
  "model": "Astra",
  "productions": [
    "modelOne": {
      "dateOfCreation": "2019-09-30T10:15:25.026+00:00",
      "dateOfEstimation": "2017-09-30T10:15:25.026+00:00",
      "someOnterInfo": "whatever"
    },
    "modelTwo": {
      "dateOfCreation": "2017-09-30T10:15:25.026+00:00",
      "dateOfEstimation": "2019-09-30T10:15:25.026+00:00",
      "someOnterInfo": "whatever"
    }
  ]
}

待交

car: {
  "model": "Astra",
  "earliestDateOfEstimation": "2017-09-30T10:15:25.026+00:00",
  "earliestDateOfCreation": "2017-09-30T10:15:25.026+00:00"
}

我怎样才能做到这一点？

Answer 1

我假设在您开始聚合时 modelOne 和 modelTwo 是未知的。关键步骤是运行$map 和$objectToArray 以消除这两个值。然后你可以使用$min 来获取“最早”的值：

db.collection.aggregate([
    {
        $addFields: {
            dates: {
                $map: {
                    input: "$car.productions",
                    in: {
                        $let: {
                            vars: { model: { $arrayElemAt: [ { $objectToArray: "$$this" }, 0 ] } },
                            in: "$$model.v"
                        }
                    }
                }
            }
        }
    },
    {
        $project: {
            _id: 1,
            "car.model": 1,
            "car.earliestDateOfEstimation": { $min: "$dates.dateOfEstimation" },
            "car.earliestDateOfCreation": { $min: "$dates.dateOfCreation" },
        }
    }
])

Mongo Playground

编辑：

如果总是有modelOne, 'modelTwo'...（固定数字），第一步可以简化

db.collection.aggregate([
    {
        $addFields: {
            dates: { $concatArrays: [ "$car.productions.modelOne", "$car.productions.modelTwo" ] }
        }
    },
    {
        $project: {
            _id: 1,
            "car.model": 1,
            "car.earliestDateOfEstimation": { $min: "$dates.dateOfEstimation" },
            "car.earliestDateOfCreation": { $min: "$dates.dateOfCreation" },
        }
    }
])

Mongo Playground (2)