MongoDB Connection in Node.js

Learn how to connect Node.js with MongoDB, create collections, insert documents, retrieve data, update records, delete records, and build a simple REST API.

1. Why Use MongoDB with Node.js?

Node.js handles application logic and HTTP requests, while MongoDB stores the application's data.

2. MongoDB vs MySQL

3. Install MongoDB

You can use either a local MongoDB installation or MongoDB Atlas.

4. Create a Node.js Project

Create a folder named node-mongodb-app.

mkdir node-mongodb-app
cd node-mongodb-app
npm init -y

The npm init -y command creates a default package.json file.

5. Install MongoDB and Express

Install the official MongoDB driver and Express:

npm install mongodb express

6. Understand Databases, Collections, and Documents

MongoDB organizes data using three important concepts:

Example Student Document

{
    "name": "Rahul Kumar",
    "email": "rahul@example.com",
    "course": "Node.js",
    "age": 20
}

MongoDB stores documents in BSON, a binary representation of JSON-like data. The driver converts documents to and from JavaScript objects.

7. Connect Node.js with MongoDB

Create a file named db.js.

const { MongoClient } = require("mongodb");

const uri = process.env.MONGODB_URI ||
    "mongodb://127.0.0.1:27017";

const client = new MongoClient(uri);

let db;

async function connectDB() {
    if (!db) {
        await client.connect();

        db = client.db("school_db");

        console.log("MongoDB connected successfully!");
    }

    return db;
}

module.exports = {
    connectDB,
    client
};

Explanation

• MongoClient is used to connect to MongoDB.
• uri contains the database connection string.
• client.connect() establishes the connection.
• client.db("school_db") selects the database.
• connectDB() returns the database object.

8. Test the MongoDB Connection

Create a file named test-db.js.

const { connectDB, client } = require("./db");

async function testConnection() {
    try {
        const db = await connectDB();

        await db.command({ ping: 1 });

        console.log("Database is ready!");
    } catch (error) {
        console.error("MongoDB connection failed:", error.message);
    } finally {
        await client.close();
    }
}

testConnection();

Run the file:

node test-db.js

Expected Output

MongoDB connected successfully!
Database is ready!

9. Insert a Document into MongoDB

Use insertOne() to add one student document to the collection.

const { connectDB, client } = require("./db");

async function addStudent() {
    try {
        const db = await connectDB();

        const result = await db.collection("students").insertOne({
            name: "Rahul Kumar",
            email: "rahul@example.com",
            course: "Node.js",
            age: 20
        });

        console.log("Student added successfully!");
        console.log("Inserted ID:", result.insertedId);
    } catch (error) {
        console.error("Error:", error.message);
    } finally {
        await client.close();
    }
}

addStudent();

Important Methods

• db.collection("students") selects a collection.
• insertOne() inserts one document.
• result.insertedId returns the new document's ID.

10. Retrieve All Documents

Use find() and toArray() to retrieve the documents from a collection.

const { connectDB, client } = require("./db");

async function getStudents() {
    try {
        const db = await connectDB();

        const students = await db
            .collection("students")
            .find({})
            .toArray();

        console.log(students);
    } catch (error) {
        console.error("Error:", error.message);
    } finally {
        await client.close();
    }
}

getStudents();

Example Output

[
    {
        _id: ObjectId("..."),
        name: "Rahul Kumar",
        email: "rahul@example.com",
        course: "Node.js",
        age: 20
    }
]

MongoDB automatically assigns an _id field to a document when you do not provide one.

11. Find a Student by Name

Use findOne() to retrieve the first document matching a condition.

const { connectDB, client } = require("./db");

async function findStudent() {
    try {
        const db = await connectDB();

        const student = await db.collection("students").findOne({
            name: "Rahul Kumar"
        });

        if (!student) {
            console.log("Student not found");
        } else {
            console.log(student);
        }
    } catch (error) {
        console.error("Error:", error.message);
    } finally {
        await client.close();
    }
}

findStudent();

12. Update a Document

Use updateOne() with $set to change selected fields in an existing document.

const { connectDB, client } = require("./db");

async function updateStudent() {
    try {
        const db = await connectDB();

        const result = await db.collection("students").updateOne(
            { email: "rahul@example.com" },
            {
                $set: {
                    course: "Full Stack Development"
                }
            }
        );

        if (result.matchedCount === 0) {
            console.log("Student not found");
        } else {
            console.log("Matched:", result.matchedCount);
            console.log("Modified:", result.modifiedCount);
        }
    } catch (error) {
        console.error("Error:", error.message);
    } finally {
        await client.close();
    }
}

updateStudent();

The first argument identifies the document. The second argument contains the update operation.

13. Delete a Document

Use deleteOne() to remove one matching document.

const { connectDB, client } = require("./db");

async function deleteStudent() {
    try {
        const db = await connectDB();

        const result = await db.collection("students").deleteOne({
            email: "rahul@example.com"
        });

        if (result.deletedCount === 0) {
            console.log("Student not found");
        } else {
            console.log("Student deleted successfully!");
        }
    } catch (error) {
        console.error("Error:", error.message);
    } finally {
        await client.close();
    }
}

deleteStudent();

14. Create a REST API with Express and MongoDB

Now let's create an Express API that connects to MongoDB and provides endpoints for student records.

Create a file named server.js.

const express = require("express");
const { connectDB, client } = require("./db");

const app = express();

app.use(express.json());

// GET all students
app.get("/students", async (req, res) => {
    try {
        const db = await connectDB();

        const students = await db
            .collection("students")
            .find({})
            .toArray();

        res.json(students);
    } catch (error) {
        console.error(error);

        res.status(500).json({
            message: "Unable to retrieve students"
        });
    }
});

// POST a new student
app.post("/students", async (req, res) => {
    try {
        const { name, email, course } = req.body;

        if (
            typeof name !== "string" || !name.trim() ||
            typeof email !== "string" || !email.trim() ||
            typeof course !== "string" || !course.trim()
        ) {
            return res.status(400).json({
                message: "Name, email, and course are required"
            });
        }

        const db = await connectDB();

        const result = await db.collection("students").insertOne({
            name: name.trim(),
            email: email.trim(),
            course: course.trim()
        });

        res.status(201).json({
            message: "Student added successfully",
            id: result.insertedId
        });
    } catch (error) {
        console.error(error);

        res.status(500).json({
            message: "Unable to add student"
        });
    }
});

// Start the server after connecting to MongoDB
async function startServer() {
    try {
        await connectDB();

        const PORT = process.env.PORT || 5000;

        app.listen(PORT, () => {
            console.log(`Server running on port ${PORT}`);
        });
    } catch (error) {
        console.error("Unable to start server:", error.message);
        process.exitCode = 1;
    }
}

startServer();

Run the server:

node server.js

15. Test the API Using Postman

For a POST request, select Body → raw → JSON and enter:

{
    "name": "Priya Sharma",
    "email": "priya@example.com",
    "course": "React"
}

Click Send. A successful insertion should return HTTP status code 201 Created.

16. MongoDB Query Methods

17. Common MongoDB Connection Errors

18. Practical Assignment

{
    "name": "Aman Kumar",
    "email": "aman@example.com",
    "course": "Node.js"
}

19. Lesson Summary