Having issue with aggregation in MongoDB - node.js

Question

I'm using MongoDb with Node.js. And I'm having trouble with aggregation.This is the Example of data in Collection in Database:
{
"name": "abcdef",
"address": ghijk,
"reli":"A",
"prov:"a" ,
}
{
"name": "xyz",
"address": "vwz",
"reli":"B",
"prov:"b" ,
}
{
"name": "qwe",
"address": "rty",
"reli":'C',
"prov:"c" ,
},
{
"name": "abcdef",
"address": ghijk,
"reli":"A",
"prov:"a" ,
}
{
"name": "hat",
"address": "ate",
"reli":'C',
"prov:"c" ,
},
This is my query to count:
const count = await db.aggregate([
{
$facet: {
"reli": [
{ $group: { _id: '$reli', count: { $sum: 1 } } }
],
"prov": [
{ $group: { _id: '$prov', count: { $sum: 1 } } }
],
This is my result of the query:
[
{
"reli": [
{
"_id": "A",
"count": 2
},
{
"_id": "B",
"count": 1
},
{
"_id": "C",
"count": 2
}
"prov": [
{
"_id": "a",
"count": 2
},
{
"_id": "b",
"count": 1
},
{
"_id": "c",
"count": 2
}
}]
I want to aggregate this data. And only want values for every reli and prov and it's count in my results.
Expecting Output:
[
"reli":{
A:2 // As my Collection has 2 "A" And 2 is it's count
C:2 // As there is 2 "C" in Collection.
}
"prov":{
c:2 //As there are 2 "c" in Collection.
b:1 //As there are 1 "b" in Collection
}
]

Answer 1

You can use $arrayToObject to get what you want here, creating keys from your values. For example:
db.collection.aggregate([
{
$facet: {
reli: [
{$group: { _id: "$reli", v: {$sum: 1}}},
{$project: {v: 1, k: "$_id", _id: 0}}
],
prov: [
{$group: {_id: "$prov", v: {$sum: 1}}},
{$project: {v: 1, k: "$_id", _id: 0}}
]
}
},
{
$project: {
prov: {$arrayToObject: "$prov"},
reli: {$arrayToObject: "$reli"}
}
}
])
Playground example
If there is a correlation between the reli and prov group, as in your example, you can avoid the $facet, group once, count once and only project twice.

Answer 2

You may try to use $group like this, the output isn't exactly like expected, but it may help you :
const reli = await db.collection.aggregate([
{
'$group': {
'_id': '$reli',
'count': {
'$sum': 1
}
}
}, {
'$project': {
'_id': 0,
'reli': '$_id',
'count': 1
}
}
])
const prov = await db.collection.aggregate([
{
'$group': {
'_id': '$prov',
'count': {
'$sum': 1
}
}
}, {
'$project': {
'_id': 0,
'prov': '$_id',
'count': 1
}
}
])
const res = {
reli,
prov
};
output :
{
"prov": [
{ "count": 2, "prov": "a" },
{ "count": 1, "prov": "b" },
{ "count": 2, "prov": "c" }
],
"reli": [
{ "count": 2, "reli": "A" },
{ "count": 2, "reli": "C" },
{ "count": 1, "reli": "B" }
]
}
From this data, if you need it, you could re write key:value, for exact data model as you asked.