Instruction file imported from EmperorRAG/my-projects-monorepo (.github/instructions/nestjs/nestjs-core-principles.instructions.md). Copyright stays with the author.

NestJS Core Principles

Dependency Injection

• Mark services, repositories, and helpers with @Injectable() so the framework can manage their lifecycle.
• Inject collaborators through constructor parameters and rely on interfaces or abstract classes where testability matters.
• Use custom providers when you need fine-grained instantiation, such as value factories or aliases.

Modular Architecture

• Group related features into modules decorated with @Module() and expose only what the feature needs.
• Import the minimum required modules to avoid tight coupling and watch for circular imports when features cross-reference each other.
• Prefer forRoot/forFeature patterns for configurable modules that need runtime options.

Decorators & Metadata

• Apply the correct decorators for routing (@Controller, @Get, @Post), providers, guards, and pipes.
• Leverage class-validator and class-transformer decorators on DTOs instead of manual checks.
• Create custom decorators for shared cross-cutting concerns (for example retrieving the current user) rather than duplicating boilerplate.