MongoDB - Aggregation Query want to match 2 _id - node.js

Question

I want to keep only that data in counts which will be matched with it's parent id for each individual document.
Student Schema
const StudentSchema = new mongoose.Schema(
{
name: {
type: String,
required: [true, "Please Provide Name"],
maxlength: 100,
minlength: 2,
},
email: {
type: String,
required: [true, "Please Provide Email"],
match: [
/^(([^<>()[\]\\.,;:\s#"]+(\.[^<>()[\]\\.,;:\s#"]+)*)|(".+"))#((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$/,
"Please Provide a Valid Email",
],
unique: true,
},
number: {
type: String,
required: [true, "Please Provide Number"],
match: [
/^(?:(?:\+|0{0,2})91(\s*[\-]\s*)?|[0]?)?[789]\d{9}$/,
"Please Provide a Valid Number",
],
unique: true,
},
rollNumber: {
type: Number,
required: [true, "Please Provide Roll Number"],
maxlength: 5,
},
departmentID: {
type: mongoose.Types.ObjectId,
ref: "Department",
required: [true, "Please Provide departmentID"],
},
classID: {
type: mongoose.Types.ObjectId,
ref: "Class",
required: [true, "Please Provide classID"],
},
position: {
type: String,
required: [true, "Please Provide Position"],
enum: ["Student"],
default: "Student",
},
password: {
type: String,
required: [true, "Please Provide Password"],
minlength: 6,
},
},
{ timestamps: true }
);
Attendance Schema
const AttendanceSchema = new Schema(
{
date: {
type: String,
required: [true, "Please Provide Date"],
maxlength: 15,
minlength: 5,
},
subjectID: {
type: mongoose.Types.ObjectId,
ref: "Subject",
required: [true, "Please Provide Subject"],
},
studentID: {
type: mongoose.Types.ObjectId,
ref: "Student",
required: [true, "Please Provide Student"],
},
teacherID: {
type: mongoose.Types.ObjectId,
ref: "Faculty",
required: [true, "Please Provide Teacher"],
},
classID: {
type: mongoose.Types.ObjectId,
ref: "Class",
required: [true, "Please Provide Class"],
},
departmentID: {
type: mongoose.Types.ObjectId,
ref: "Department",
required: [true, "Please Provide Department"],
},
},
{ timestamps: true }
);
My Query
const data = await StudentSchema.aggregate([
{ $match: { classID: mongoose.Types.ObjectId(`${req.params.id}`) } },
{
$lookup: {
from: "attendances",
pipeline: [
{
$match: {
subjectID: mongoose.Types.ObjectId(`${req.params.Sid}`),
},
},
{ $group: { _id: "$studentID", count: { $sum: 1 } } },
],
as: "counts",
},
},
]);
This is the data I'm getting from this query:
{
"data": [
{
"_id": "63677d2960fa65e95aef5e95",
"name": "Lavannya Urkande",
"email": "lavannya#gmail.com",
"number": "9130354519",
"rollNumber": 201,
"departmentID": "6365531fdc02a121ffeed944",
"classID": "636554e8dc02a121ffeed982",
"position": "Student",
"password": "$2a$10$mqysVgtIGrYbvMGtHE2vbu0z5g05BlwJizcc.CfWMld78VPrnvcrO",
"createdAt": "2022-11-06T09:23:53.803Z",
"updatedAt": "2022-11-06T09:23:53.803Z",
"__v": 0,
"counts": [
{
"_id": "6367819d60fa65e95aef5ea7",
"count": 2,
},
{
"_id": "63677d2960fa65e95aef5e95",
"count": 3,
}
]
},
{
"_id": "6367819d60fa65e95aef5ea7",
"name": "Sohan Shinde",
"email": "soham#gmail.com",
"number": "9130354510",
"rollNumber": 202,
"departmentID": "6365531fdc02a121ffeed944",
"classID": "636554e8dc02a121ffeed982",
"position": "Student",
"password": "$2a$10$DuXjtayCPgGwkNnpog5IYeEEkY56igtlA/m6vobT44wmlSLcXp1eK",
"createdAt": "2022-11-06T09:42:53.861Z",
"updatedAt": "2022-11-06T09:42:53.861Z",
"__v": 0,
"counts": [
{
"_id": "6367819d60fa65e95aef5ea7",
"count": 2,
},
{
"_id": "63677d2960fa65e95aef5e95",
"count": 3,
}
]
}
]
}
But I want this type of data from my query(counts)
The only data which matched with it's parent _id. Notice the _id and counts._id then you can understand my request.
{
"data": [
{
"_id": "63677d2960fa65e95aef5e95",
"name": "Lavannya Urkande",
"email": "lavannya#gmail.com",
"number": "9130354519",
"rollNumber": 201,
"departmentID": "6365531fdc02a121ffeed944",
"classID": "636554e8dc02a121ffeed982",
"position": "Student",
"password": "$2a$10$mqysVgtIGrYbvMGtHE2vbu0z5g05BlwJizcc.CfWMld78VPrnvcrO",
"createdAt": "2022-11-06T09:23:53.803Z",
"updatedAt": "2022-11-06T09:23:53.803Z",
"__v": 0,
"counts": [
{
"_id": "63677d2960fa65e95aef5e95",
"count": 3,
}
]
},
{
"_id": "6367819d60fa65e95aef5ea7",
"name": "Sohan Shinde",
"email": "soham#gmail.com",
"number": "9130354510",
"rollNumber": 202,
"departmentID": "6365531fdc02a121ffeed944",
"classID": "636554e8dc02a121ffeed982",
"position": "Student",
"password": "$2a$10$DuXjtayCPgGwkNnpog5IYeEEkY56igtlA/m6vobT44wmlSLcXp1eK",
"createdAt": "2022-11-06T09:42:53.861Z",
"updatedAt": "2022-11-06T09:42:53.861Z",
"__v": 0,
"counts": [
{
"_id": "6367819d60fa65e95aef5ea7",
"count": 2,
}
]
}
]
}

Answer 1

You can use filter method in your $project
const data = await StudentSchema.aggregate([
{ $match: { classID: mongoose.Types.ObjectId(`${req.params.id}`) } },
{
$lookup: {
from: "attendances",
pipeline: [
{
$match: {
subjectID: mongoose.Types.ObjectId(`${req.params.Sid}`),
},
},
{ $group: { _id: "$studentID", count: { $sum: 1 } } },
],
as: "counts",
},
},
{
$project: {
classID: 1,
departmentID: 1,
email: 1,
name: 1,
number: 1,
position: 1,
rollNumber: 1,
counts: {
$filter: {
input: "$counts",
cond: {
$eq: ["$$this._id", "$_id"],
},
},
},
},
},
]);