MongoDB - 获取组的完整文档，同时考虑到一个属性的最小值

Question

下午好，我从MongoDB开始，我对组聚合有疑问。

来自以下一组文件;我需要得到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"}

我只获得了最便宜的价格，房间标识符和重复次数。

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}

调查我发现数据可以用$first或$last获得，但数据不是我需要的数据，因为它是根据文档的位置获得的。

我需要的是从这套文件中获取，每个文件都有最便宜的房间。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"}

我希望我已经解释了。

提前谢谢。

问候。

Answer 1

您可以在$group阶段添加 $ROOT 美元的捕获，然后使用$filter将房间列表与最小值进行比较。 $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 ] }
}
}
])

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