Shared Modules and Exports

A provider is visible only inside its own module. To use ProductsService in OrdersService, two things are needed: ProductsModule must export it, and OrdersModule must import ProductsModule.

src/orders/orders.module.ts

import { Module } from '@nestjs/common';
import { ProductsModule } from '../products/products.module';
import { OrdersController } from './orders.controller';
import { OrdersService } from './orders.service';

@Module({
  imports: [ProductsModule],            // gives access to exported ProductsService
  controllers: [OrdersController],
  providers: [OrdersService],
})
export class OrdersModule {}

If you forget the import or the export, the app fails on start with a clear message:

npm run start:dev

[Nest] 20112  - ERROR [ExceptionHandler] Nest can't resolve dependencies of the OrdersService (?).
Please make sure that the argument ProductsService at index [0] is available in the OrdersModule context.

Potential solutions:
- Is OrdersModule a valid NestJS module?
- If ProductsService is a provider, is it part of the current OrdersModule?
- If ProductsService is exported from a separate @Module, is that module imported within OrdersModule?