MongoDB

Question

下午好，我从MongoDB开始，我对组聚合有疑问。

来自以下一组文档；我需要获得所有类似房间中最便宜的房间（按标识符房间分组）。

{"_id":"874521035","provider":{"id":{"$numberInt":"2"},"name":"HotelBeds"},"accommodation":{"id":{"$numberInt":"36880"},"name":"Hotel Goya"},"room":{"id":{"$numberInt":"1"},"name":"Doble"},"board":{"id":{"$numberInt":"1"},"name":"Sólo alojamiento"},"fare":{"id":"NRF","name":"No reembolsable"},"price":{"cost":{"$numberInt":"115"},"net":{"$numberInt":"116"},"pvp":{"$numberInt":"126"}},"fees":{"agency":{"$numberInt":"10"},"cdv":{"$numberInt":"1"}},"cancellation-deadeline":"2019-12-31","payment-deadeline":"2019-12-30"}
{"_id":"123456789","provider":{"id":{"$numberInt":"2"},"name":"HotelBeds"},"accommodation":{"id":{"$numberInt":"36880"},"name":"Hotel Goya"},"room":{"id":{"$numberInt":"1"},"name":"Doble"},"board":{"id":{"$numberInt":"2"},"name":"Alojamiento y desayuno"},"fare":{"id":"NOR","name":"Reembolsable"},"price":{"cost":{"$numberInt":"120"},"net":{"$numberInt":"121"},"pvp":{"$numberInt":"131"}},"fees":{"agency":{"$numberInt":"10"},"cdv":{"$numberInt":"1"}},"cancellation-deadeline":"2019-12-31","payment-deadeline":"2019-12-30"}
{"_id":"987654321","provider":{"id":{"$numberInt":"2"},"name":"HotelBeds"},"accommodation":{"id":{"$numberInt":"36880"},"name":"Hotel Goya"},"room":{"id":{"$numberInt":"2"},"name":"Triple"},"board":{"id":{"$numberInt":"1"},"name":"Sólo alojamiento"},"fare":{"id":"NOR","name":"Reembolsable"},"price":{"cost":{"$numberInt":"125"},"net":{"$numberInt":"126"},"pvp":{"$numberInt":"136"}},"fees":{"agency":{"$numberInt":"10"},"cdv":{"$numberInt":"1"}},"cancellation-deadeline":"2019-12-31","payment-deadeline":"2019-12-30"}
{"_id":"852963147","provider":{"id":{"$numberInt":"2"},"name":"HotelBeds"},"accommodation":{"id":{"$numberInt":"36880"},"name":"Hotel Goya"},"room":{"id":{"$numberInt":"3"},"name":"Doble uso individual"},"board":{"id":{"$numberInt":"1"},"name":"Sólo alojamiento"},"price":{"cost":{"$numberInt":"99"},"net":{"$numberInt":"100"},"pvp":{"$numberInt":"110"}},"fees":{"agency":{"$numberInt":"10"},"cdv":{"$numberInt":"1"}},"cancellation-deadeline":"2019-12-31","payment-deadeline":"2019-12-30"}

我只获取了最便宜的价格、房间标识和重复次数。

db.consolidation.aggregate ([
{
    $group: {
        _id: "$ room.id",
        "cheapest": {$ min: "$ price.pvp"},
        "qty": {$ sum: 1}
    }
}]);

{"_id": 2, "cheapest": 136, "qty": 1}
{"_id": 3, "cheapest": 110, "qty": 1}
{"_id": 1, "cheapest": 126, "qty": 2}

查了一下发现用$first或者$last都可以得到数据，但是根据文档的位置得到的数据不是我需要的数据

我需要的是从文档集合中获取最便宜房间的每个文档。这是我期望的结果：

{"_id":"874521035","provider":{"id":{"$numberInt":"2"},"name":"HotelBeds"},"accommodation":{"id":{"$numberInt":"36880"},"name":"Hotel Goya"},"room":{"id":{"$numberInt":"1"},"name":"Doble"},"board":{"id":{"$numberInt":"1"},"name":"Sólo alojamiento"},"fare":{"id":"NRF","name":"No reembolsable"},"price":{"cost":{"$numberInt":"115"},"net":{"$numberInt":"116"},"pvp":{"$numberInt":"126"}},"fees":{"agency":{"$numberInt":"10"},"cdv":{"$numberInt":"1"}},"cancellation-deadeline":"2019-12-31","payment-deadeline":"2019-12-30"}
{"_id":"987654321","provider":{"id":{"$numberInt":"2"},"name":"HotelBeds"},"accommodation":{"id":{"$numberInt":"36880"},"name":"Hotel Goya"},"room":{"id":{"$numberInt":"2"},"name":"Triple"},"board":{"id":{"$numberInt":"1"},"name":"Sólo alojamiento"},"fare":{"id":"NOR","name":"Reembolsable"},"price":{"cost":{"$numberInt":"125"},"net":{"$numberInt":"126"},"pvp":{"$numberInt":"136"}},"fees":{"agency":{"$numberInt":"10"},"cdv":{"$numberInt":"1"}},"cancellation-deadeline":"2019-12-31","payment-deadeline":"2019-12-30"}
{"_id":"852963147","provider":{"id":{"$numberInt":"2"},"name":"HotelBeds"},"accommodation":{"id":{"$numberInt":"36880"},"name":"Hotel Goya"},"room":{"id":{"$numberInt":"3"},"name":"Doble uso individual"},"board":{"id":{"$numberInt":"1"},"name":"Sólo alojamiento"},"price":{"cost":{"$numberInt":"99"},"net":{"$numberInt":"100"},"pvp":{"$numberInt":"110"}},"fees":{"agency":{"$numberInt":"10"},"cdv":{"$numberInt":"1"}},"cancellation-deadeline":"2019-12-31","payment-deadeline":"2019-12-30"}

希望我已经解释清楚了。

提前致谢。

此致。

Answer 1

您可以添加捕获 $$ROOT as part of your $group stage and then use $filter to compare a list of your rooms against min value. $replaceRoot 将允许您获得原始形状：

db.collection.aggregate([
    {
        $group: {
            _id: "$room.id",
            "cheapest": {
                $min: "$price.pvp"
            },
            "qty": { $sum: 1 },
            docs: { $push: "$$ROOT" }
        }
    },
    {
        $replaceRoot: {
            newRoot: { $arrayElemAt: [ { $filter: { input: "$docs", cond: { $eq: [ "$$this.price.pvp", "$cheapest" ] } } }, 0 ] }
        }
    }
])

Mongo Playground

MongoDB - 获取一个组的完整文档，考虑到一个属性的最小值

MongoDB - Obtain full document of a group taking into account the minimum value of one property

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