Async configuration

When you need to pass module options asynchronously instead of statically, use the forRootAsync() method. As with most dynamic modules, Nest provides several techniques to deal with async configuration.

One technique is to use a factory function:

TelegrafModule.forRootAsync({
  useFactory: () => ({
    token: 'TELEGRAM_BOT_TOKEN',
  }),
});

Like other factory providers, our factory function can be async and can inject dependencies through inject.

TelegrafModule.forRootAsync({
  imports: [ConfigModule.forFeature(telegrafModuleConfig)],
  useFactory: async (configService: ConfigService) => ({
    token: configService.get<string>('TELEGRAM_BOT_TOKEN'),
  }),
  inject: [ConfigService],
});

Alternatively, you can configure the TelegrafModule using a class instead of a factory, as shown below:

TelegrafModule.forRootAsync({
  useClass: TelegrafConfigService,
});

The construction above instantiates TelegrafConfigService inside TelegrafModule, using it to create the required options object. Note that in this example, the TelegrafConfigService has to implement the TelegrafOptionsFactory interface, as shown below. The TelegrafModule will call the createTelegrafOptions() method on the instantiated object of the supplied class.

@Injectable()
class TelegrafConfigService implements TelegrafOptionsFactory {
  createTelegrafOptions(): TelegrafModuleOptions {
    return {
      token: 'TELEGRAM_BOT_TOKEN',
    };
  }
}

If you want to reuse an existing options provider instead of creating a private copy inside the TelegrafModule, use the useExisting syntax.

TelegrafModule.forRootAsync({
  imports: [ConfigModule.forFeature(telegrafModuleConfig)],
  useExisting: ConfigService,
});