MongoDB + Mongoose

Now we’re diving into MongoDB (a NoSQL database) and Mongoose (an ODM for Node.js). This is a core part of building backend apps with Node.js for flexible, schema-based data handling. Let’s go step by step.

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1️⃣ What is MongoDB?

• NoSQL database → stores data as documents (JSON-like objects) instead of tables.

• Flexible schema → fields can vary between documents.

• Great for scalable, dynamic applications.

Example document:

{
  "_id": "64f72e4f12b34abc12345def",
  "name": "Tyson",
  "email": "tyson@example.com",
  "age": 30
}

• Collections = tables (e.g., users, posts)

• Documents = rows (individual entries)

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2️⃣ Mongoose Overview

• Mongoose = ODM (Object Data Modeling) library for MongoDB.

• Provides schemas, models, and validation on top of MongoDB.

• Lets you interact with MongoDB using JS objects instead of raw queries.

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3️⃣ Install MongoDB + Mongoose

npm install mongoose

Make sure you have a MongoDB instance running (local or cloud e.g., MongoDB Atlas).

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4️⃣ Connecting to MongoDB

const mongoose = require("mongoose");
 
mongoose.connect("mongodb://localhost:27017/myapp", {
  useNewUrlParser: true,
  useUnifiedTopology: true,
})
  .then(() => console.log("MongoDB connected"))
  .catch((err) => console.error("DB connection error:", err));

• useNewUrlParser and useUnifiedTopology are recommended options.

• Connection returns a Promise → use async/await if preferred.

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5️⃣ Defining a Schema & Model

const { Schema, model } = mongoose;
 
// Define schema
const userSchema = new Schema({
  name: { type: String, required: true },
  email: { type: String, required: true, unique: true },
  age: { type: Number, min: 0 },
  createdAt: { type: Date, default: Date.now }
});
 
// Create model
const User = model("User", userSchema);

• Schema = structure + validation rules

• Model = interface to query and manipulate data

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6️⃣ CRUD Operations with Mongoose

Create

const newUser = await User.create({ name: "Tyson", email: "tyson@example.com", age: 30 });
console.log(newUser);

Read

const users = await User.find(); // all users
const singleUser = await User.findOne({ email: "tyson@example.com" });

Update

const updatedUser = await User.findByIdAndUpdate(newUser._id, { age: 31 }, { new: true });

Delete

await User.findByIdAndDelete(newUser._id);

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7️⃣ Querying & Filtering

// Filter + sort + limit
const result = await User.find({ age: { $gte: 18 } }) // age >= 18
  .sort({ name: 1 })   // ascending by name
  .limit(10);

• $gte, $lte, $in, $ne → MongoDB query operators

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8️⃣ Relationships (References)

• One-to-Many example: Users → Posts

const postSchema = new Schema({
  title: String,
  content: String,
  author: { type: Schema.Types.ObjectId, ref: "User" }
});
 
const Post = model("Post", postSchema);
 
// Populate author details
const posts = await Post.find().populate("author");

• populate() = fetch related documents

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✅ Summary

Concept	MongoDB	Mongoose
Type	NoSQL, document-oriented	ODM (Object Data Modeling) library
Data	Collections & Documents	Schema + Model abstraction
Queries	JSON-like	Chainable JS methods (find, create)
Validation	Optional	Built-in schema validation
Relationships	References & embedding	populate() for references

Key Takeaways:

• MongoDB = flexible, scalable NoSQL database

• Mongoose = adds schemas, validation, and easy queries

• Combine with Node.js + Express for full REST APIs

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