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[英]MongoDB: How to merge all documents into a single document in an aggregation pipeline
[英]How to regroup (or merge) objects in aggregation pipeline in MongoDB?
我目前有一個聚合管道:
db.getCollection('forms').aggregate([
{ $unwind: //unwind },
{
$match: {
//some matches
}
},
{
$project: {
//some projections
}
},
{
//Finally, im grouping the results
$group: {
_id: {
year: { $year: '$createdAt' },
month: { $month: '$createdAt' },
raceEthnicity: '$demographic.raceEthnicity'
},
count: { $sum: 1 },
}
]
我目前的結果類似於:
[{
"_id" : {
"year" : 2020,
"month" : 11,
"raceEthnicity" : "Asian"
},
"count" : 1.0
},
{
"_id" : {
"year" : 2020,
"month" : 11,
"raceEthnicity" : "Multiracial"
},
"count" : 3.0
},
{
"_id" : {
"year" : 2020,
"month" : 11,
"raceEthnicity" : "White"
},
"count" : 3.0
},
{
"_id" : {
"year" : 2020,
"month" : 10,
"raceEthnicity" : "White"
},
"count" : 33.0
}]
有沒有辦法在管道上添加一個新階段以將同一年/月的結果“合並”到一個對象中? 我想實現以下目標:
{
"_id" : {
"year" : 2020,
"month" : 11,
},
"Asian" : 1.0,
"Multiracial": 3.0,
"White": 1.0
},
{
"_id" : {
"year" : 2020,
"month" : 10,
},
"White": 33
}
是否可以? 我怎樣才能做到這一點?
將此添加到您的聚合管道中。
db.collection.aggregate([
{ $set: { "data": { k: "$_id.raceEthnicity", v: "$count" } } },
{ $group: { _id: { year: "$_id.year", month: "$_id.month" }, data: { $push: "$data" } } },
{ $set: { "data": { $arrayToObject: "$data" } } },
{ $replaceRoot: { newRoot: { $mergeObjects: ["$$ROOT", "$data"] } } },
{ $unset: "data" }
])
與@wak786 的解決方案不同,您不需要在設計時了解所有種族。 它適用於任意種族。
將這些階段添加到您的管道中。
db.collection.aggregate([
{
$replaceRoot: {
newRoot: {
"$mergeObjects": [
"$$ROOT",
{
$arrayToObject: [
[
{
k: "$_id.raceEthnicity",
v: "$count"
}
]
]
}
]
}
}
},
{
"$group": {
"_id": {
year: "$_id.year",
month: "$_id.month",
},
"Asian": {
"$sum": "$Asian"
},
"Multiracial": {
"$sum": "$Multiracial"
},
"White": {
"$sum": "$White"
}
}
}
])
下面是 mongo 游樂場鏈接。 我已將您管道的當前結果作為查詢的輸入。
在這里試試
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