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Provider的多种写法 ​

1. 基础写法 ​

  1. 声明一个Provider
js
@Injectable()
class AppService {

}
@Injectable()
class AppService {

}
  1. Module中注册
js
@Module({
  providers: [
    AppService
  ]
})
export class AppModule {}
@Module({
  providers: [
    AppService
  ]
})
export class AppModule {}
  1. 依赖注入
js
@Controller()
class AppController {
  constructor(private readonly appService: AppService){}
}
@Controller()
class AppController {
  constructor(private readonly appService: AppService){}
}

或者

js
@Controller()
class AppController {
  @Inject(AppService)
  private readonly appService: AppService
}
@Controller()
class AppController {
  @Inject(AppService)
  private readonly appService: AppService
}

2. provide、useClass ​

  1. 基础写法等同于以下写法：
js
@Module({
  providers: [
    {
      provide: AppService,
      useClass: AppService
    }
  ]
})
export class AppModule {}
@Module({
  providers: [
    {
      provide: AppService,
      useClass: AppService
    }
  ]
})
export class AppModule {}
  1. 字符串注入
js
@Module({
  providers: [
    {
      provide: 'app_service',
      useClass: AppService
    }
  ]
})
@Module({
  providers: [
    {
      provide: 'app_service',
      useClass: AppService
    }
  ]
})
js
@Controller()
class AppController {
  constructor(@Inject('app_service') private readonly appService: AppService){}
}
@Controller()
class AppController {
  constructor(@Inject('app_service') private readonly appService: AppService){}
}

3. useValue ​

js
@Module({
  providers: [
    {
      provide: 'app_service',
      useValue: {
        a: '123'
      }
    }
  ]
})
@Module({
  providers: [
    {
      provide: 'app_service',
      useValue: {
        a: '123'
      }
    }
  ]
})
js
@Controller()
class AppController {
  constructor(@Inject('app_service') private readonly appService: { a: string }){}
}
@Controller()
class AppController {
  constructor(@Inject('app_service') private readonly appService: { a: string }){}
}

4. useFactory ​

  1. 基础用法
js
@Module({
  providers: [
    {
      provide: 'app_service',
      useFactory() {
        return {
          a: '123'
        }
      }
    }
  ]
})
@Module({
  providers: [
    {
      provide: 'app_service',
      useFactory() {
        return {
          a: '123'
        }
      }
    }
  ]
})
js
@Controller()
class AppController {
  constructor(@Inject('app_service') private readonly appService: { a: string }){}
}
@Controller()
class AppController {
  constructor(@Inject('app_service') private readonly appService: { a: string }){}
}
  1. 参数注入

useFactory可以接受其他被注入的Service对象

js
@Module({
  providers: [
    {
      provide: 'app_service',
      useFactory(otherService, otherService1, otherService2) {
        return {
          a: '123'
        }
      },
      inject: [OtherService, 'service_xxx']
    }
  ],
})
@Module({
  providers: [
    {
      provide: 'app_service',
      useFactory(otherService, otherService1, otherService2) {
        return {
          a: '123'
        }
      },
      inject: [OtherService, 'service_xxx']
    }
  ],
})
  1. 异步useFactory
js
@Module({
  providers: [
    {
      provide: 'app_service',
      async useFactory(otherService, otherService1, otherService2) {

        await fn()...
        return {
          a: '123'
        }
      }
    }
  ]
})
@Module({
  providers: [
    {
      provide: 'app_service',
      async useFactory(otherService, otherService1, otherService2) {

        await fn()...
        return {
          a: '123'
        }
      }
    }
  ]
})

5. useExisting ​

provider 还可以通过 useExisting 来指定别名, 比如下面的，给app_service 起了个别名叫app_service_1

js
@Module({
  providers: [
    {
      provide: 'app_service_1',
      useExisting: 'app_service'
    }
  ]
})
@Module({
  providers: [
    {
      provide: 'app_service_1',
      useExisting: 'app_service'
    }
  ]
})