Mongoose¶

Mongoose is an Object Data Modeling (ODM) library for MongoDB and Node.js. It helps developers interact with MongoDB using JavaScript objects instead of writing raw database queries.

Why Use Mongoose?¶

Provides Schema-based data modeling.
Offers validation, middleware, and query helpers.
Handles relationships and data population.
Simplifies CRUD operations with a clean API.
Automatically converts JavaScript objects into MongoDB documents.

Installation¶

npm install mongoose

Connecting to MongoDB¶

import mongoose from "mongoose";

async function connectDB() {
  try {
    await mongoose.connect("mongodb://localhost:27017/myDatabase");
    console.log("MongoDB connected!");
  } catch (err) {
    console.error(err);
  }
}

connectDB();

Defining a Schema¶

A schema defines the structure of documents within a collection.

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

Creating a Model¶

A model is a wrapper around a MongoDB collection that provides CRUD methods.

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

CRUD Operations¶

1. Create¶

const newUser = new User({ name: "Luke", age: 16, email: "Luke@example.com" });
await newUser.save();

2. Read¶

const users = await User.find(); // Get all users
const user = await User.findOne({ name: "Luke" }); // Find one
const userById = await User.findById("id_here"); // Find by ID

3. Update¶

await User.updateOne({ name: "Luke" }, { age: 17 });
await User.findByIdAndUpdate("id_here", { age: 18 }, { new: true });

4. Delete¶

await User.deleteOne({ name: "Luke" });
await User.findByIdAndDelete("id_here");

Schema Types¶

Common field types:

String, Number, Boolean, Date, Array, ObjectId, Buffer

Example:

const postSchema = new mongoose.Schema({
  title: String,
  content: String,
  tags: [String],
  author: { type: mongoose.Schema.Types.ObjectId, ref: "User" },
  date: { type: Date, default: Date.now }
});

Schema Validation¶

const productSchema = new mongoose.Schema({
  name: { type: String, required: true },
  price: { type: Number, min: 0 },
  inStock: { type: Boolean, default: true }
});

Middleware (Hooks)¶

Run logic before or after actions like saving or deleting.

userSchema.pre("save", function (next) {
  console.log("Saving user:", this.name);
  next();
});

Virtuals¶

Computed fields that are not stored in the database.

userSchema.virtual("info").get(function () {
  return `${this.name} (${this.age} years old)`;
});

Populate (Relations)¶

Used to fetch related documents from another collection.

const post = await Post.find().populate("author");

Example Project Structure¶

project/
├── models/
│   └── userModel.js
├── index.js
└── package.json

userModel.js

import mongoose from "mongoose";

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

export default mongoose.model("User", userSchema);

index.js

import mongoose from "mongoose";
import User from "./models/userModel.js";

await mongoose.connect("mongodb://localhost:27017/testDB");
const user = await User.create({ name: "Luke", email: "Luke@gmail.com", age: 16 });
console.log(user);