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NestJS Implementation Guide ​

Applying architectural principles in NestJS applications at Synapse Studios

Foundation: Clean Architecture | Modular Monolith | Use Cases

Overview ​

This guide demonstrates how we implement our core architectural principles in NestJS applications. NestJS provides an excellent foundation for building maintainable, testable backend services that follow Clean Architecture patterns.

Key Principles in NestJS ​

🏗️ Structure ​

We build modular monoliths using NestJS modules as bounded contexts, each containing its own Clean Architecture layers.

🧱 Separation of Concerns ​

Business logic remains framework-agnostic, with NestJS-specific code confined to the infrastructure layer.

🔌 Dependency Injection ​

NestJS's powerful DI container helps us implement the Dependency Inversion Principle and maintain loose coupling between modules.

🧪 Testing ​

Our architecture enables fast unit tests for business logic and comprehensive integration tests for APIs.

Guide Structure ​

Architecture & Design ​

Modular Monolith in NestJS ​

How to structure NestJS applications as modular monoliths with clear boundaries and independent modules.

Clean Architecture in NestJS Modules ​

Implementing the three-layer architecture (domain, use cases, infrastructure) within NestJS modules.

Repository Pattern in NestJS ​

Abstracting data persistence through domain-focused interfaces and NestJS providers.

Dependency Cruiser Configuration ​

Complete configuration and rules for enforcing architectural boundaries automatically.

Testing ​

Unit Testing in NestJS ​

Testing domain logic and use cases in isolation without framework dependencies.

Integration Testing in NestJS ​

End-to-end testing of REST APIs with real databases and full module wiring.

Quick Reference ​

Module Structure ​

src/modules/orders/
├── domain/           # Entities, value objects, domain services
├── use-cases/        # Application business logic
├── infrastructure/   # Controllers, repositories, module definition
└── tests/           # Module-specific tests

Key Patterns ​

  • Controllers → Inbound adapters (infrastructure layer)
  • Use Cases → Application services (use case layer)
  • Repositories → Outbound ports (interfaces in domain, implementations in infrastructure)
  • Entities → Core business objects (domain layer)

Common Decorators & Patterns ​

typescript
@Module()           // Define module boundaries
@Injectable()       // Mark services for DI
@Controller()       // HTTP adapters
@Get(), @Post()     // Route handlers

Getting Started ​

  1. Start with Modular Monolith in NestJS to understand module organization
  2. Review Clean Architecture in NestJS Modules for layer implementation
  3. Study Repository Pattern for data access patterns
  4. Learn testing strategies in Unit Testing and Integration Testing

Concepts ​

External ​