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.

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🍃 Why Use MongoDB?

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

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🧰 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

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🔧 Installing MongoDB and Mongoose

npm install mongoose

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

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🌐 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");
});

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🧱 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;

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📦 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));

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🔍 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));

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✏️ 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)
);

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❌ Deleting Documents

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

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

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⚙️ 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 },
});

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🧠 Middleware (Hooks)

Pre-save hook example:

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

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🔗 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));

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🛡️ Indexes and Performance

userSchema.index({ email: 1 });

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🧪 Testing with MongoDB Memory Server

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

Use in tests:

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

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📁 Project Structure Example

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

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