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.