Retrieving different aggregated fields with mongoose - node.js

Question

I am trying to wrap my head around the query which I am trying to make with mongoose on Node JS. Here is my dataset:
{"_id":{"$oid":"5e49c389e3c23a1da881c1c9"},"name":"New York","good_incidents":{"$numberInt":"50"},"salary":{"$numberInt":"50000"},"bad_incidents":"30"}
{"_id":{"$oid":"5e49c3bbe3c23a1da881c1ca"},"name":"Cairo","bad_incidents":{"$numberInt":"59"},"salary":{"$numberInt":"15000"}}
{"_id":{"$oid":"5e49c42de3c23a1da881c1cb"},"name":"Berlin","incidents":{"$numberInt":"30"},"bad_incidents":"15","salary":{"$numberInt":"55000"}}
{"_id":{"$oid":"5e49c58ee3c23a1da881c1cc"},"name":"New York","good_incidents":{"$numberInt":"15"},"salary":{"$numberInt":"56500"}}
What I am trying to do is get these values:
The most repeated city in collection
The average of bad_incidents
The maximum value of good_incidents
Maximum salary where there are no bad_incidents
I am trying to wrap my head around how I can do this in one query, because I only need one value per field. I would be glad if somebody would lead me on the right track. No need for full solution
Regards!

Answer 1

You may perform MongoDB aggregation with $facet operator which allows compute several aggregation at once.
db.collection.aggregate([
{
$facet: {
repeated_city: [
{
$group: {
_id: "$name",
name: {
$first: "$name"
},
count: {
$sum: 1
}
}
},
{
$match: {
count: {
$gt: 1
}
}
},
{
$sort: {
count: -1
}
},
{
$limit: 1
}
],
bad_incidents: [
{
$group: {
_id: null,
avg_bad_incidents: {
$avg: {
$toInt: "$bad_incidents"
}
}
}
}
],
good_incidents: [
{
$group: {
_id: null,
max_good_incidents: {
$max: {
$toInt: "$good_incidents"
}
}
}
}
],
max_salary: [
{
$match: {
bad_incidents: {
$exists: false
}
}
},
{
$group: {
_id: null,
max_salary: {
$max: {
$toInt: "$salary"
}
}
}
}
]
}
},
{
$replaceWith: {
$mergeObjects: [
{
$arrayElemAt: [
"$repeated_city",
0
]
},
{
$arrayElemAt: [
"$bad_incidents",
0
]
},
{
$arrayElemAt: [
"$good_incidents",
0
]
},
{
$arrayElemAt: [
"$max_salary",
0
]
}
]
}
}
])
MongoPlayground
[
{
"_id": null,
"avg_bad_incidents": 34.666666666666664,
"count": 2,
"max_good_incidents": 50,
"max_salary": 56500,
"name": "New York"
}
]