在 MongoDB 中分组并添加到 Group
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【中文标题】在 MongoDB 中分组并添加到 Group【英文标题】：Grouping in MongoDB and adding to Group 【发布时间】：2021-03-14 07:14:59 【问题描述】：我有一个MeterReadings 集合，如下所示。
"_id" : ObjectId("5fc768b33561870a262813c6"),
"installedAppId" : "A",
"readings" : [
"n" : "daf43d66-6c3b-4553-80af-6a0b1cf97418:power",
"t" : 1606902984662,
"u" : "W",
"v" : 100
]
"_id" : ObjectId("5fc768c73561870a262813c7"),
"installedAppId" : "B",
"readings" : [
"n" : "daf43d66-6c3b-4553-80af-6a0b1cf97418:power",
"t" : 1606902984662,
"u" : "W",
"v" : 200
]
"_id" : ObjectId("5fc768e43561870a262813c8"),
"installedAppId" : "A",
"readings" : [
"n" : "daf43d66-6c3b-4553-80af-6a0b1cf97418:power",
"t" : 1606902984672,
"u" : "W",
"v" : 300
]
我想要的输出是按installedAppId 分组，然后将每个readings 从所有匹配的installedAppId 中附加到一个条目中。下面显示的是我的目标。
"_id" : ObjectId("5fc768b33561870a262813c6"),
"installedAppId" : "A",
"readings" : [
"n" : "daf43d66-6c3b-4553-80af-6a0b1cf97418:power",
"t" : 1606902984662,
"u" : "W",
"v" : 100
,
"n" : "daf43d66-6c3b-4553-80af-6a0b1cf97418:power",
"t" : 1606902984672,
"u" : "W",
"v" : 300
]
"_id" : ObjectId("5fc768c73561870a262813c7"),
"installedAppId" : "B",
"readings" : [
"n" : "daf43d66-6c3b-4553-80af-6a0b1cf97418:power",
"t" : 1606902984662,
"u" : "W",
"v" : 200
]
按installedAppId 分组确实会使用上述数据返回两个组。
> db.MeterReadings.aggregate([ $group: _id: installedAppId: "$installedAppId" ])
"_id" : "installedAppId" : "B"
"_id" : "installedAppId" : "A"
由于每个读数都不同，尽管在 $group 中添加 readings 作为另一个条目与查询整个数据库相同。
> db.MeterReadings.aggregate([ $group: _id: installedAppId: "$installedAppId", readings: "$readings" ]).pretty()
"_id" :
"installedAppId" : "A",
"readings" : [
"n" : "daf43d66-6c3b-4553-80af-6a0b1cf97418:power",
"t" : 1606902984672,
"u" : "W",
"v" : 10.2
]
"_id" :
"installedAppId" : "B",
"readings" : [
"n" : "daf43d66-6c3b-4553-80af-6a0b1cf97418:power",
"t" : 1606902984662,
"u" : "W",
"v" : 10.2
]
"_id" :
"installedAppId" : "A",
"readings" : [
"n" : "daf43d66-6c3b-4553-80af-6a0b1cf97418:power",
"t" : 1606902984662,
"u" : "W",
"v" : 10.2
]
欢迎任何帮助！
【问题讨论】：
【参考方案1】：$push 或 $addToSet 似乎都可以解决问题，但是为每个添加数组。如果可以只推送到一个数组会更好。
addToSet
> db.MeterReadings.aggregate([$group : _id : "$installedAppId", readings: $addToSet : "$readings"]).pretty()
"_id" : "B",
"readings" : [
[
"n" : "daf43d66-6c3b-4553-80af-6a0b1cf97418:power",
"t" : 1606902984672,
"u" : "W",
"v" : 200
]
]
"_id" : "A",
"readings" : [
[
"n" : "daf43d66-6c3b-4553-80af-6a0b1cf97418:power",
"t" : 1606902984672,
"u" : "W",
"v" : 300
],
[
"n" : "daf43d66-6c3b-4553-80af-6a0b1cf97418:power",
"t" : 1606902984672,
"u" : "W",
"v" : 100
]
]
推
> db.MeterReadings.aggregate([$group : _id : "$installedAppId", readings: $push: "$readings"]).pretty()
"_id" : "B",
"readings" : [
[
"n" : "daf43d66-6c3b-4553-80af-6a0b1cf97418:power",
"t" : 1606902984672,
"u" : "W",
"v" : 200
]
]
"_id" : "A",
"readings" : [
[
"n" : "daf43d66-6c3b-4553-80af-6a0b1cf97418:power",
"t" : 1606902984672,
"u" : "W",
"v" : 100
],
[
"n" : "daf43d66-6c3b-4553-80af-6a0b1cf97418:power",
"t" : 1606902984672,
"u" : "W",
"v" : 300
]
]
【讨论】：
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