nestjs-best-practices

Avoid circular dependencies by extracting shared logic into a third module that both modules import, or by using event-driven communication with @nestjs/event-emitter. Forward references exist but indicate architectural problems and are the leading cause of runtime crashes.

Organize by feature modules rather than technical layers, keeping each feature's controllers, services, entities, and DTOs together in one directory. This enables faster onboarding and development compared to grouping all controllers or services separately.

Yes, constructor injection is the preferred pattern because dependencies are explicit, testable, and visible in the class signature. Property injection hides dependencies and complicates mocking in unit tests with the NestJS testing module.

Use DTOs with class-validator decorators and a global ValidationPipe configured with whitelist and transform options. Built-in pipes like ParseUUIDPipe and ParseIntPipe handle common type conversions and reject invalid input automatically.

Use custom repositories when services contain complex query logic such as query builders with joins, grouping, or conditional filters. This keeps services focused on business logic, simplifies mocking in tests, and isolates database implementation details.

Providing a service in multiple modules creates separate instances with independent state, causing memory waste and inconsistent behavior. Instead, define the service in one dedicated module, export it, and import that module wherever the service is needed.