Express.js Database Basics
Most real-world applications need to store data permanently – user accounts, products, orders, blog posts. This is where **databases** come in. In this chapter, we'll learn the basics of integrating databases with Express.js applications.
What is a Database?
A database is an organized collection of data stored electronically. Think of it as a digital filing cabinet where you can store, retrieve, and manipulate data efficiently.
If Express is your restaurant's kitchen, the database is your cold storage and pantry – it's where all the ingredients (data) are kept until needed.
Types of Databases
| Type | Description | Examples |
|---|---|---|
| Relational (SQL) | Data organized in tables with rows and columns. Uses structured query language (SQL). | MySQL, PostgreSQL, SQLite |
| Non-relational (NoSQL) | Flexible data models – documents, key-value pairs, graphs. | MongoDB, Firebase, Redis |
How Express Communicates with Databases
Express itself doesn't talk directly to databases. Instead, we use **database drivers** or **ODM/ORM libraries**:
- Database Driver: Low-level library that speaks the database's protocol (e.g., `mysql2`, `pg` for PostgreSQL).
- ODM (Object Document Mapper): For NoSQL databases – maps documents to JavaScript objects (e.g., Mongoose for MongoDB).
- ORM (Object Relational Mapper): For SQL databases – maps tables to JavaScript objects (e.g., Sequelize, TypeORM).
Basic Database Connection Pattern
Regardless of which database you choose, the pattern is similar:
- Install the database driver/ORM.
- Create a connection to the database.
- Use the connection in your routes to query data.
- Close the connection when your app shuts down.
Environment Variables for Database Credentials
Never hardcode database credentials! Use environment variables:
<!-- .env file -->DB_HOST=localhostDB_USER=rootDB_PASSWORD=secretDB_NAME=mydb
<!-- In your app -->require('dotenv').config();
const dbConfig = { host: process.env.DB_HOST, user: process.env.DB_USER, password: process.env.DB_PASSWORD, database: process.env.DB_NAME};Two Minute Drill
- Databases store persistent data for your Express applications.
- Two main types: SQL (relational) and NoSQL (non-relational).
- Express uses drivers/ORMs to communicate with databases.
- Always store database credentials in environment variables.
- Choose the right database based on your data structure and application needs.
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