Clean Architecture & Domain-Driven Design in NestJS

Most NestJS tutorials stop at controllers calling services calling a database. This course is about what comes after that: how to structure a real backend so business logic lives in one place, is fully unit-testable, and doesn't fall apart when requirements change.

Together we build a complete e-commerce system from scratch - products, customers, orders, and payments - as four autonomous bounded contexts, applying Domain-Driven Design and Clean Architecture patterns to every layer.

What you'll learn to build:

• Rich domain models with aggregates, entities, and value objects — where invalid state is unrepresentable, and every state change goes through behavior methods

• CQRS with commands, queries, and handlers using @nestjs/cqrs

• Domain events emitted from business logic — and sagas that orchestrate workflows across bounded contexts (order placed → payment created → order confirmed)

• Ports and adapters: swap PostgreSQL (Drizzle) for MongoDB, or console notifications for real email notifications via Mailtrap, by changing a single line

• Child entities with their own state machines whose status drives the parent aggregate

• Real integrations: Stripe payments with webhook handling & Mailtrap email notifications

• A clean REST API layer with DTOs and validation that dispatches commands and never touches domain objects directly

Every concept is introduced in order: value objects first, then entities, aggregates, collection invariants, and finally cross-context orchestration. You never see a pattern before you have the foundation for it.