MongoDB with Node.js

Mongoose adds models and application-level schemas on top of the MongoDB driver. Its validation is not a substitute for collection validation when other clients also write data.

MongoDB can be accessed in Node.js using a powerful Object Data Modeling (ODM) library called Mongoose. It allows you to define schemas, models, and provides a convenient API to interact with the database — making your code clean and manageable.

Before working through the examples, make sure you can connect with mongosh and select your database. Use a practice database for writes and deletions.

Mongoose is an npm package that acts as a bridge between MongoDB and your Node.js application. It lets you define models with a schema and provides methods to perform CRUD operations.

Question: Why not use the native MongoDB driver?

Answer: While the native driver works fine, Mongoose offers schema validation, middleware, and a more developer-friendly API, especially for beginners.

Installing Mongoose

Before we begin, let’s set up a new Node.js project and install Mongoose.

    mkdir mongoose-demo
    cd mongoose-demo
    npm init -y
    npm install mongoose

Connecting to MongoDB

Create a file called app.js and add the following connection code:

// app.js
const mongoose = require('mongoose');

mongoose.connect('mongodb://127.0.0.1:27017/mongoose_course')
  .then(() => console.log("Connected to MongoDB"))
  .catch(err => console.error("Connection failed", err));

    Connected to MongoDB

Explanation: The URI points to a local MongoDB instance on port 27017. If you’re using MongoDB Atlas, replace the URI with your cluster's connection string.

Let’s define a simple User model with fields like name, email, and age.

const userSchema = new mongoose.Schema({
  name: String,
  email: { type: String, required: true, unique: true },
  age: Number
});

const User = mongoose.model('User', userSchema);

Explanation: The schema defines the structure of a document. User becomes a model which represents the users collection in MongoDB.

Inserting a Document

Add this code in app.js after the model declaration to create a new user.

async function createUser() {
  const user = new User({
    name: "Alice",
    email: "alice@example.com",
    age: 28
  });

  const result = await user.save();
  console.log(result);
}

createUser();

    {
      _id: ObjectId("..."),
      name: 'Alice',
      email: 'alice@example.com',
      age: 28,
      __v: 0
    }

Question: What is __v in the output?

Answer: Mongoose adds a version key __v by default for internal versioning. It helps with concurrency control and can be ignored in most beginner cases.

To find all users:

async function getUsers() {
  const users = await User.find();
  console.log(users);
}

getUsers();

    [ { _id: ObjectId("..."), name: 'Alice', email: 'alice@example.com', age: 28, __v: 0 } ]

To filter users by age:

const youngUsers = await User.find({ age: { $lt: 30 } });

Updating a Document

Let’s update Alice’s age.

async function updateUser() {
  const result = await User.updateOne({ name: "Alice" }, {
    $set: { age: 29 }
  });
  console.log(result);
}

updateUser();

    { acknowledged: true, modifiedCount: 1, matchedCount: 1 }

Question: What does matchedCount mean?

Answer: It shows how many documents matched the filter condition. modifiedCount tells how many were actually updated.

To delete Alice from the database:

async function deleteUser() {
  const result = await User.deleteOne({ name: "Alice" });
  console.log(result);
}

deleteUser();

    { acknowledged: true, deletedCount: 1 }

Mongoose adds models and application-level schemas on top of the MongoDB driver. Its validation is not a substitute for collection validation when other clients also write data.

Summary

In this lesson, you learned how to:

• Set up Mongoose in a Node.js project
• Define a schema and create a model
• Perform CRUD operations with ease

Mongoose abstracts away the complexity of dealing with raw MongoDB queries, making it easier to build full-stack applications. In the next topic, we'll use MongoDB Atlas to connect your application to a cloud-hosted MongoDB cluster.

• Separate authentication from permissions