How to fetch data from multiple collections in MongoDB? - mongodb

Question

How to fetch data from multiple collections in MongoDB by using a common field and sending data (in those fetched collections) using one response?
Employee Scheema:
const mongoose = require("mongoose");
const employeeSchema = new mongoose.Schema(
{
profilePic: {
type: String,
},
employeeID: {
type: String,
required: true,
},
employeeFirstName: {
type: String,
required: true,
},
employeeLastName: {
type: String,
required: true,
},
birthday: {
type: String,
},
streetNo: {
type: String,
},
city: {
type: String,
},
phoneNumber: {
type: String,
},
jobRole: {
type: String,
required: true,
},
NIC: {
type: String,
required: true,
unique: true,
},
companyEmail: {
type: String,
required: true,
unique: true,
},
status: {
type: String,
required: true,
},
resignDate: {
type: String,
},
jobType: {
type: String,
required: true,
},
candidateID: {
type: String,
required: true,
},
teamID: {
type: String,
},
lastSeen: {
type: String,
},
token: {
type: String,
},
},
{ timestamps: true }
);
module.exports = mongoose.model("employee", employeeSchema);
Acadamic Qualification Scheema:
const mongoose = require("mongoose");
const academicQualificaationSchema = new mongoose.Schema(
{
employeeID: {
type: String,
required: true,
},
ordinaryLevelResult: {
type: Array,
required: true,
},
advancedLevelResults: {
type: Array,
required: true,
},
achievements: {
type: Array,
required: true,
},
},
{ timestamps: true }
);
module.exports = mongoose.model(
"academicQualification",
academicQualificaationSchema
);
Professional Qualification Scheema:
const mongoose = require("mongoose");
const proffesionalQualificaationSchema = new mongoose.Schema(
{
employeeID: {
type: String,
required: true,
},
degree: {
type: Array,
required: true,
},
language: {
type: Array,
required: true,
},
course: {
type: Array,
required: true,
},
},
{ timestamps: true }
);
module.exports = mongoose.model(
"proffesionalQualification",
proffesionalQualificaationSchema
);
Controller:
exports.viewEmployees = async (req, res) => {
try {
let accQuali, profQuali;
const employees = await employeeSchema.find();
accQuali = await academicQualificaationSchema.find();
profQuali = await ProffesionalQualificationSchema.find();
if (employees || accQuali || profQuali) {
return res.status(200).json({ data: { employees, profQuali, accQuali } });
} else {
return res.status(404).json({ message: message });
}
} catch (err) {
return res.status(404).json({ err: err.message });
}
};
This controller is working properly and sends all data in 3 collections with the use of one response. But, I am comfortable if I will be able to Fetch data separately for each employee.

Answer 1

If you want to get the data from the three collections for specific employee or employees, you can use an aggregation pipeline with a $lookup stage, as suggested by #1sina1. For example:
db.employee.aggregate([
{
$match: {"employeeID": "IDA"}
},
{
$lookup: {
from: "academicQualification",
localField: "employeeID",
foreignField: "employeeID",
as: "academicQualification"
}
},
{
$lookup: {
from: "proffesionalQualification",
localField: "employeeID",
foreignField: "employeeID",
as: "proffesionalQualification"
}
}
])
As you can see on the playground