nestjs-best-practices

NestJS Best Practices

Overview

Grounded in the Official NestJS Documentation, this skill enforces modular architecture, dependency injection scoping, exception filters, DTO validation with class-validator, and Drizzle ORM integration patterns.

When to Use

• Designing/refactoring NestJS modules or dependency injection
• Creating exception filters, validating DTOs, or integrating Drizzle ORM
• Reviewing code for anti-patterns or onboarding to a NestJS codebase

Instructions

1. Modular Architecture

Follow strict module encapsulation. Each domain feature should be its own @Module():

• Export only what other modules need — keep internal providers private
• Use forwardRef() only as a last resort for circular dependencies; prefer restructuring
• Group related controllers, services, and repositories within the same module
• Use a SharedModule for cross-cutting concerns (logging, configuration, caching)

See references/arch-module-boundaries.md for enforcement rules.

2. Dependency Injection

Choose the correct provider scope based on use case:

Scope	Lifecycle	Use Case
DEFAULT	Singleton (shared)	Stateless services, repositories
REQUEST	Per-request instance	Request-scoped data (tenant, user context)
TRANSIENT	New instance per injection	Stateful utilities, per-consumer caches

• Default to DEFAULT scope — only use REQUEST or TRANSIENT when justified
• Use constructor injection exclusively — avoid property injection
• Register custom providers with useClass, useValue, useFactory, or useExisting

See references/di-provider-scoping.md for enforcement rules.

3. Request Lifecycle

Understand and respect the NestJS request processing pipeline:

Middleware → Guards → Interceptors (before) → Pipes → Route Handler → Interceptors (after) → Exception Filters

• Middleware: Cross-cutting concerns (logging, CORS, body parsing)
• Guards: Authorization and authentication checks (return true/false)
• Interceptors: Transform response data, add caching, measure timing
• Pipes: Validate and transform input parameters
• Exception Filters: Catch and format error responses

4. Error Handling