What is the nestjs error handling approach (business logic error vs. http error)?

Let’s assume your business logic throws an EntityNotFoundError and you want to map it to a NotFoundException.

For that, you can create an Interceptor that transforms your errors:

@Injectable()
export class NotFoundInterceptor implements NestInterceptor {
  intercept(context: ExecutionContext, next: CallHandler): Observable<any> {
    // next.handle() is an Observable of the controller's result value
    return next.handle()
      .pipe(catchError(error => {
        if (error instanceof EntityNotFoundError) {
          throw new NotFoundException(error.message);
        } else {
          throw error;
        }
      }));
  }
}

You can then use it by adding @UseInterceptors(NotFoundInterceptor) to your controller’s class or methods; or even as a global interceptor for all routes. Of course, you can also map multiple errors in one interceptor.

Try it out in this codesandbox.