Projecting flat values from nested objects - node.js

Question

I am writing a small aggregation in mongoose to filter values from db and return them in order of frequency they occur.
For example:
Say multiple documents have partners array as a field, which is an array of objects, each having two values "partner_id" and "passed_tests". I want to return all the unique partners from all the documents sorted according to their frequency in the collection in decreasing order.
Here is a sample document:
{
"location": "eindhoven",
"partners": [
{
"partner_id": 3,
"passed_tests": true
},
{
"partner_id": 2,
"passed_tests": false
}
],
"_id": "3136323031333066306d4438",
"uid": "d95f2e446c052514c097e6c925408774",
"__v": 0,
"is_approved": true
}
My code is as follows:
function returnAll(callback) {
TestService.aggregate([
{
$match: { "is_approved": true }
},
{
$unwind: "$partners"
}, {
$group: {
"_id": {
partner: { $objectToArray: "$partners" },
partner_id: { $arrayElemAt: ["$partner", 0] }
},
"count": { "$sum": 1 }
}
},
{
$sort: { "count": -1 }
},
{
$project: {
"partner_values": {
$map: {
input: "$_id.partner",
as: "el",
in: {
$cond: {
if: {
$or: [{ $eq: ["$$el.v", true] },
{ $eq: ["$$el.v", false] }]
}, then: {
"passed_tests": "$$el.v"
}, else: {
"id": "$$el.v"
}
}
}
}
},
"count": "$count,
"_id": 0
}
},
], function (error, data) {
if (error) {
logger.error(error);
callback(null);
} else {
callback(data);
}
});
}
Which returns this JSON to my node app:
"data": [
{
"partner_values": [
{
"id": 2
},
{
"passed_tests": false
}
],
"count": 3
},
{
"partner_values": [
{
"id": 6
},
{
"passed_tests": true
}
],
"count": 1
},
{
"partner_values": [
{
"id": 3
},
{
"passed_tests": true
}
],
"count": 1
},
{
"partner_values": [
{
"id": 1
},
{
"passed_tests": true
}
],
"count": 1
}
]
If I don't use the projection pipeline in my aggregation, I get this:
"data": [
{
"_id": {
"partner": [
{
"k": "partner_id",
"v": 2
},
{
"k": "passed_tests",
"v": false
}
],
"partner_id": null
},
"count": 3
},
{
"_id": {
"partner": [
{
"k": "partner_id",
"v": 6
},
{
"k": "passed_tests",
"v": true
}
],
"partner_id": null
},
"count": 1
},
{
"_id": {
"partner": [
{
"k": "partner_id",
"v": 3
},
{
"k": "passed_tests",
"v": true
}
],
"partner_id": null
},
"count": 1
},
{
"_id": {
"partner": [
{
"k": "partner_id",
"v": 1
},
{
"k": "passed_tests",
"v": true
}
],
"partner_id": null
},
"count": 1
}
]
which is quite understandable as I am introducing "_id" and other extra fields to look into the array and find the value. However, the output I want is:
"data": {
"partners": [{
"id": 2,
"passed_tests": false,
"count": 3
}, {
"id": 6,
"passed_tests": false,
"count": 1
}, {
"id": 3,
"passed_tests": false,
"count": 1
}, {
"id": 1,
"passed_tests": false,
"count": 1
}]
}
Can I get some help on this, please? Thanks.

Answer 1

You can use below aggregation query.
TestService.aggregate([
{"$match":{"is_approved":true}},
{"$unwind":"$partners"},
{"$group":{
"_id":{"partner_id":"$partners.partner_id","passed_tests":"$partners.passed_tests"},
"count":{"$sum":1}
}},
{"$sort":{"count":-1}},
{"$group":{
"_id":null,
"partners":{"$push":{"id":"$_id.partner_id","passed_tests":"$_id.passed_tests","count":"$count"}}
}},
{"$project":{"partners":1}}
])