**Course Title:** Modern JavaScript Programming: From Fundamentals to Full-Stack Development **Section Title:** Back-End Development with Node.js and Express **Topic:** Connecting to a database (MongoDB or PostgreSQL) and handling CRUD operations **Overview** ----------- In this topic, we'll explore how to connect to a database and perform CRUD (Create, Read, Update, Delete) operations using Node.js and Express. We'll cover two popular databases, MongoDB and PostgreSQL, and learn how to interact with them using popular Node.js libraries. **Why Databases Matter** ------------------------ Databases are a crucial part of any web application, as they store and manage data that's used to provide a rich user experience. In this topic, we'll learn how to connect to a database, perform CRUD operations, and integrate our Express application with the database to store and retrieve data. **Connecting to a MongoDB Database** ------------------------------------- For MongoDB, we'll use the Mongoose library, which provides a simple and intuitive way to interact with MongoDB. ### Installing Mongoose ```bash npm install mongoose ``` ### Connecting to a MongoDB Database ```javascript // Import Mongoose const mongoose = require('mongoose'); // Connection string const mongoUrl = 'mongodb://localhost:27017/mydatabase'; // Connect to MongoDB mongoose.connect(mongoUrl, { useNewUrlParser: true, useUnifiedTopology: true }); // Create a schema const userSchema = new mongoose.Schema({ name: String, age: Number }); // Create a model const User = mongoose.model('User', userSchema); ``` **Connecting to a PostgreSQL Database** -------------------------------------- For PostgreSQL, we'll use the pg library, which provides a simple and efficient way to interact with PostgreSQL. ### Installing pg ```bash npm install pg ``` ### Connecting to a PostgreSQL Database ```javascript // Import pg const { Pool } = require('pg'); // Connection string const pgUrl = 'postgresql://username:password@localhost:5432/mydatabase'; // Create a pool const pool = new Pool({ connectionString: pgUrl }); ``` **CRUD Operations** ------------------- Once we've connected to our database, we can perform CRUD operations to manage data. Let's use Mongoose to perform CRUD operations on a MongoDB database. ### Create ```javascript // Create a new user const user = new User({ name: 'John Doe', age: 30 }); user.save((err, user) => { if (err) console.error(err); console.log(user); }); ``` ### Read ```javascript // Find all users User.find((err, users) => { if (err) console.error(err); console.log(users); }); // Find a user by ID User.findById('5f676a1a34b76f0ec0a76a7d', (err, user) => { if (err) console.error(err); console.log(user); }); ``` ### Update ```javascript // Update a user User.findByIdAndUpdate('5f676a1a34b76f0ec0a76a7d', { name: 'Jane Doe' }, (err, user) => { if (err) console.error(err); console.log(user); }); ``` ### Delete ```javascript // Delete a user User.findByIdAndRemove('5f676a1a34b76f0ec0a76a7d', (err, user) => { if (err) console.error(err); console.log(user); }); ``` **Integrating with Express** --------------------------- Once we've connected to our database and performed CRUD operations, we can integrate our Express application with the database to store and retrieve data. ### Adding a User ```javascript // Import Express const express = require('express'); const app = express(); // Import Mongoose const User = require('./models/user'); // Create a new user app.post('/users', (req, res) => { const user = new User({ name: req.body.name, age: req.body.age }); user.save((err, user) => { if (err) console.error(err); res.json(user); }); }); ``` ### Getting All Users ```javascript // Get all users app.get('/users', (req, res) => { User.find((err, users) => { if (err) console.error(err); res.json(users); }); }); ``` **Conclusion** ---------- In this topic, we've learned how to connect to a database (MongoDB or PostgreSQL) and perform CRUD operations using Node.js and Express. We've also seen how to integrate our Express application with the database to store and retrieve data. For more information on MongoDB and Mongoose, please visit the [Mongoose documentation](https://mongoosejs.com/docs/). For more information on PostgreSQL and pg, please visit the [pg documentation](https://node-postgres.com). **Practical Takeaways** ------------------------ * Connect to a database using Mongoose or pg * Perform CRUD operations using Mongoose or pg * Integrate an Express application with a database * Use Express to create, read, update, and delete data in a database **What's Next?** ----------------- In the next topic, we'll learn about the importance of testing in modern JavaScript applications. **Do you have any questions or need help with anything? Please leave a comment below.**

npm install mongoose

// Import Mongoose
const mongoose = require('mongoose');

// Connection string
const mongoUrl = 'mongodb://localhost:27017/mydatabase';

// Connect to MongoDB
mongoose.connect(mongoUrl, { useNewUrlParser: true, useUnifiedTopology: true });

// Create a schema
const userSchema = new mongoose.Schema({
  name: String,
  age: Number
});

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

npm install pg

// Import pg
const { Pool } = require('pg');

// Connection string
const pgUrl = 'postgresql://username:password@localhost:5432/mydatabase';

// Create a pool
const pool = new Pool({
  connectionString: pgUrl
});

// Create a new user
const user = new User({ name: 'John Doe', age: 30 });
user.save((err, user) => {
  if (err) console.error(err);
  console.log(user);
});

// Find all users
User.find((err, users) => {
  if (err) console.error(err);
  console.log(users);
});

// Find a user by ID
User.findById('5f676a1a34b76f0ec0a76a7d', (err, user) => {
  if (err) console.error(err);
  console.log(user);
});

// Update a user
User.findByIdAndUpdate('5f676a1a34b76f0ec0a76a7d', { name: 'Jane Doe' }, (err, user) => {
  if (err) console.error(err);
  console.log(user);
});

// Delete a user
User.findByIdAndRemove('5f676a1a34b76f0ec0a76a7d', (err, user) => {
  if (err) console.error(err);
  console.log(user);
});

// Import Express
const express = require('express');
const app = express();

// Import Mongoose
const User = require('./models/user');

// Create a new user
app.post('/users', (req, res) => {
  const user = new User({ name: req.body.name, age: req.body.age });
  user.save((err, user) => {
    if (err) console.error(err);
    res.json(user);
  });
});

// Get all users
app.get('/users', (req, res) => {
  User.find((err, users) => {
    if (err) console.error(err);
    res.json(users);
  });
});