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61 lines
2.0 KiB
Markdown
61 lines
2.0 KiB
Markdown
---
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id: async-configuration
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title: Async configuration
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sidebar_label: Async configuration
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slug: /async-configuration
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---
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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.
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One technique is to use a factory function:
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```typescript
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TelegrafModule.forRootAsync({
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useFactory: () => ({
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token: 'TELEGRAM_BOT_TOKEN',
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}),
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});
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```
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Like other [factory providers](https://docs.nestjs.com/fundamentals/custom-providers#factory-providers-usefactory), our factory function can be async and can inject dependencies through inject.
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```typescript
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TelegrafModule.forRootAsync({
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imports: [ConfigModule.forFeature(telegrafModuleConfig)],
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useFactory: async (configService: ConfigService) => ({
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token: configService.get<string>('TELEGRAM_BOT_TOKEN'),
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}),
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inject: [ConfigService],
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});
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```
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Alternatively, you can configure the TelegrafModule using a class instead of a factory, as shown below:
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```typescript
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TelegrafModule.forRootAsync({
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useClass: TelegrafConfigService,
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});
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```
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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.
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```typescript
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@Injectable()
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class TelegrafConfigService implements TelegrafOptionsFactory {
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createTelegrafOptions(): TelegrafModuleOptions {
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return {
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token: 'TELEGRAM_BOT_TOKEN',
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};
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}
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}
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```
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If you want to reuse an existing options provider instead of creating a private copy inside the `TelegrafModule`, use the `useExisting` syntax.
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```typescript
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TelegrafModule.forRootAsync({
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imports: [ConfigModule.forFeature(telegrafModuleConfig)],
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useExisting: ConfigService,
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});
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```
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