Databases Introduction in Node

Introduction

Persistent apps store data in databases—PostgreSQL, MySQL, MongoDB, Redis, and others. Node does not include a database engine; you install a driver or ORM and connect over the network or local socket. This chapter explains concepts and a minimal PostgreSQL-style flow without binding you to one vendor.

Prerequisites

• HTTP clients in Node
• Environment variables
• Async/await

SQL vs Document Stores (Brief)

Choose based on data relationships, team skills, and ops constraints.

Connection String in Env

DATABASE_URL=postgres://user:pass@localhost:5432/myapp

Never commit real credentials—use .env locally and secrets in production.

Raw SQL with pg (Conceptual)

npm install pg

$1 placeholders prevent SQL injection—never interpolate user strings into SQL.

ORM Example Sketch (Prisma-style)

ORMs map tables to JavaScript objects and generate migrations:

// Pseudocode — actual API depends on library
// const user = await prisma.user.create({ data: { email, name } });

Good for rapid development; learn SQL fundamentals anyway.

MongoDB Sketch

// Conceptual — mongodb driver
// const doc = await collection.findOne({ email });
// await collection.insertOne({ email, name, createdAt: new Date() });

Flexible schema; enforce shape in application code or JSON Schema.

Redis for Cache

// Cache expensive query result 60 seconds
// await redis.set(`user:${id}`, JSON.stringify(user), "EX", 60);
// const cached = await redis.get(`user:${id}`);

Not a replacement for primary storage—cache and session store use cases.

Transactions (SQL)

Mini Example: In-Memory Repo (Tests)

Swap implementation behind the same functions when adding PostgreSQL.

FAQ

SQLite for learning?

Yes—single file, zero server—great for local tutorials and tests.

Connection pooling?

Reuse pools (pg.Pool)—opening a connection per request is slow.

Migrations?

Version schema with SQL migration files or ORM tools—never edit production tables by hand without a plan.

What comes next?

Course wrap-up, then async/await and message queues.