Node.js with MongoDB: Database, Collections, and CRUD

What is MongoDB?

MongoDB is a NoSQL, document-oriented database. Instead of tables and rows, it stores data as flexible JSON-like documents (BSON) grouped into collections inside a database.

Connecting Node.js to MongoDB

npm install mongodb

const { MongoClient } = require('mongodb');
const uri = 'mongodb://localhost:27017';
const client = new MongoClient(uri);

async function main() {
    await client.connect();
    console.log('Connected to MongoDB');

    // Create/select a database
    const db = client.db('schoolDB');

    // Create/select a collection
    const students = db.collection('students');

    // ... CRUD operations go here

    await client.close();
}

main().catch(console.error);

MongoDB creates the database and collection automatically the first time data is written to them — no explicit CREATE DATABASE step is required.

Insert

// Insert one document
await students.insertOne({ name: 'Alice', age: 20, course: 'CSE' });

// Insert many documents
await students.insertMany([
    { name: 'Bob', age: 22, course: 'IT' },
    { name: 'Carol', age: 21, course: 'CSE' }
]);

Query (Find)

// Find all documents
const all = await students.find({}).toArray();

// Find with a filter
const cseStudents = await students.find({ course: 'CSE' }).toArray();

// Find one document
const alice = await students.findOne({ name: 'Alice' });

// Query operators
const adults = await students.find({ age: { $gte: 18 } }).toArray();

Common Query Operators

Update

// Update one document
await students.updateOne(
    { name: 'Alice' },
    { $set: { age: 21 } }
);

// Update many documents
await students.updateMany(
    { course: 'CSE' },
    { $set: { department: 'Computer Science' } }
);

Delete

// Delete one document
await students.deleteOne({ name: 'Bob' });

// Delete many documents
await students.deleteMany({ course: 'IT' });

Sort

// Sort by age ascending (1) or descending (-1)
const byAgeAsc = await students.find({}).sort({ age: 1 }).toArray();
const byAgeDesc = await students.find({}).sort({ age: -1 }).toArray();

Join (Aggregation with $lookup)

MongoDB is not relational, but it supports join-like operations using $lookup in the aggregation pipeline:

const results = await db.collection('orders').aggregate([
    {
        $lookup: {
            from: 'students',       // collection to join
            localField: 'studentId', // field in "orders"
            foreignField: '_id',     // field in "students"
            as: 'studentDetails'
        }
    }
]).toArray();

Full CRUD Example

async function run() {
    const db = client.db('schoolDB');
    const students = db.collection('students');

    await students.insertOne({ name: 'Dave', age: 23, course: 'ECE' });
    const found = await students.find({ course: 'ECE' }).sort({ age: -1 }).toArray();
    await students.updateOne({ name: 'Dave' }, { $set: { age: 24 } });
    await students.deleteOne({ name: 'Dave' });

    console.log(found);
}

Key Takeaway: MongoDB stores flexible JSON-like documents in collections rather than rigid tables. The official mongodb driver exposes insertOne/Many, find, updateOne/Many, deleteOne/Many, .sort(), and $lookup (for join-like queries) — all through simple, promise-based async calls.