Getting Started with MongoDB and Mongoose

MongoDB is a popular NoSQL database that stores data in flexible, JSON-like documents. Mongoose is an elegant MongoDB object modeling tool for Node.js.

Why Use MongoDB?

Schema-less and flexible
High performance and scalability
Easily handles large volumes of unstructured data
Built-in replication and sharding support

Why Use Mongoose?

Mongoose adds structure and convenience on top of MongoDB:

Schema definitions
Data validation
Middleware support (pre/post hooks)
Simple API for querying and updating documents

Installing MongoDB and Mongoose

npm install mongoose

Make sure you have MongoDB installed and running locally or use MongoDB Atlas.

Connecting to MongoDB

// db.js
const mongoose = require("mongoose");

mongoose.connect("mongodb://localhost:27017/myapp", {
  useNewUrlParser: true,
  useUnifiedTopology: true,
});

const db = mongoose.connection;
db.on("error", console.error.bind(console, "connection error:"));
db.once("open", () => {
  console.log("Connected to MongoDB");
});

Defining a Schema and Model

// models/User.js
const mongoose = require("mongoose");

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

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

Creating and Saving Documents

const User = require("./models/User");

const newUser = new User({
  name: "Alice",
  email: "alice@example.com",
  age: 25,
});

newUser
  .save()
  .then((user) => console.log("User saved:", user))
  .catch((err) => console.error(err));

Querying Documents

User.find().then((users) => console.log(users));

User.findOne({ email: "alice@example.com" }).then((user) => console.log(user));

User.findById("someId").then((user) => console.log(user));

Updating Documents

User.updateOne({ email: "alice@example.com" }, { age: 30 }).then((result) =>
  console.log(result)
);

User.findByIdAndUpdate("someId", { name: "Alice Updated" }, { new: true }).then(
  (updated) => console.log(updated)
);

Deleting Documents

User.deleteOne({ email: "alice@example.com" }).then((result) =>
  console.log(result)
);

User.findByIdAndDelete("someId").then((deleted) => console.log(deleted));

Schema Validation and Defaults

Mongoose allows built-in validation:

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

Middleware (Hooks)

Pre-save hook example:

userSchema.pre("save", function (next) {
  this.name = this.name.trim();
  next();
});

Relationships (References)

const blogPostSchema = new mongoose.Schema({
  title: String,
  body: String,
  author: { type: mongoose.Schema.Types.ObjectId, ref: "User" },
});

const BlogPost = mongoose.model("BlogPost", blogPostSchema);

BlogPost.find()
  .populate("author")
  .then((posts) => console.log(posts));

Indexes and Performance

userSchema.index({ email: 1 });

Testing with MongoDB Memory Server

npm install --save-dev mongodb-memory-server

Use in tests:

const { MongoMemoryServer } = require("mongodb-memory-server");

Project Structure Example

src/
│
├── models/
│   └── User.js
├── db.js
├── app.js
└── routes/
    └── userRoutes.js