由于另一个服务注入，服务找不到依赖项

Question

我有一个 NestJs 应用程序，在我对另外两个服务（PmsConnectionService -> UserService）使用依赖注入后，以前工作的服务会引发错误（ReviewService 找不到 DoctorLoaderService）。所有这些都来自不同的模块。

我的 nestjs 版本是 5.1.0。 PmsConnectionService 是我新创建的模块的一部分。我不得不使用 forwardRef 连接到持有 DoctorLoaderService 的模块。 请注意，在下面的代码中，PmsConnectionService 注入了 DoctorClinicService，它正在注入 DoctorLoaderService。当我在 PmsConnectionService 中注释掉 DoctorClinicService 时，错误消失了。但是我仍然不知道为什么会首先发生错误。

服务

@Injectable()
export class PmsConnectionService {
    constructor(
        private clinicService: DoctorClinicService,
    ) {}

@Injectable()
export class UserService {
  constructor(
    private readonly connectionService: PmsConnectionService,
  ) { }

@Injectable()
export class DoctorLoaderService {
  constructor(
    @Inject(forwardRef(() => ReviewService))
    private readonly reviewService: ReviewService,
  ) {}

@Injectable()
export class ReviewService {
  constructor(
    private readonly doctorLoader: DoctorLoaderService,
    private readonly reviewManager: ReviewManagerService,
  ) { }

模块：

@Module({
    imports: [
        forwardRef(() => DoctorModule),
        TypeOrmModule.forFeature([
            ...
          ]),
    ],
    providers: [
        PmsConnectionService,
    ],
    exports: [
        PmsConnectionService,
    ],
})
export class PmsModule {}

@Module({
  imports: [
    PmsModule,
    TypeOrmModule.forFeature([
      User,
      ...
    ]),
  ],
  controllers: [
    UserController,
  ],
  providers: [
    UserService,
  ],
  exports: [UserService],
})
export class UserModule {
  public configure(consumer: MiddlewareConsumer) {
    consumer
      .apply(ActivityMiddleware)
      .exclude({
        path: '*',
        method: RequestMethod.OPTIONS,
      })
      .forRoutes({ path: '*', method: RequestMethod.ALL });
  }
}

@Module({
  imports: [
    UserModule,
    TypeOrmModule.forFeature([
      User,
      DoctorProfile,
      DoctorClinic,
      ...
    ]),
    forwardRef(() => BookingModule),
  ],
  controllers: [
    DoctorProfileController,
  ],
  providers: [
    DoctorLoaderService,
    DoctorClinicService,
  ],
  exports: [
    DoctorClinicService,
    DoctorLoaderService,
  ],
})
export class DoctorModule { }

Module({
  imports: [
    PmsModule,
    UserModule,
    DoctorModule,
    TypeOrmModule.forFeature([
      ...
    ]),
  ],
  controllers: [
   ...
  ],
  providers: [
    ReviewService,
  ],
  exports: [
    ReviewService,
  ],
})
export class BookingModule { }

应用程序在启动时抛出以下错误：

[Nest] 17921   - 9/26/2019, 9:44:15 PM   [NestFactory] Starting Nest application...
[Nest] 17921   - 9/26/2019, 9:44:15 PM   [ExceptionHandler] Nest can't resolve dependencies of the ReviewService (?, ReviewManagerService, NotiIssuerService). Please make sure that the argument at index [0] is available in the current context. +90ms
Error: Nest can't resolve dependencies of the ReviewService (?, ReviewManagerService, NotiIssuerService). Please make sure that the argument at index [0] is available in the current context.
    at Injector.resolveSingleParam (/Users/dude/Documents/lekar/unexpected_koala_backend/node_modules/@nestjs/core/injector/injector.js:115:19)
    at Promise.all.dependencies.map (/Users/dude/Documents/lekar/unexpected_koala_backend/node_modules/@nestjs/core/injector/injector.js:85:49)
    at Array.map (<anonymous>)
    at Injector.resolveConstructorParams (/Users/dude/Documents/lekar/unexpected_koala_backend/node_modules/@nestjs/core/injector/injector.js:83:58)
    at Injector.loadInstance (/Users/dude/Documents/lekar/unexpected_koala_backend/node_modules/@nestjs/core/injector/injector.js:63:20)
    at Injector.loadInstanceOfComponent (/Users/dude/Documents/lekar/unexpected_koala_backend/node_modules/@nestjs/core/injector/injector.js:40:20)
    at Promise.all.map (/Users/dude/Documents/lekar/unexpected_koala_backend/node_modules/@nestjs/core/injector/instance-loader.js:39:102)
    at Array.map (<anonymous>)
    at InstanceLoader.createInstancesOfComponents (/Users/dude/Documents/lekar/unexpected_koala_backend/node_modules/@nestjs/core/injector/instance-loader.js:39:59)
    at Promise.all.map (/Users/dude/Documents/lekar/unexpected_koala_backend/node_modules/@nestjs/core/injector/instance-loader.js:26:24)

虽然我认为问题出在 PmsConnectionService 和 DoctorClinicService 之间的连接上，但我不知道如何解决这个问题。

Answer 1

看起来你只设置了一半的前锋裁判。由于您的 ReviewService（BookingModule 的一部分）取决于您的 DoctorLoaderService（DoctorModule 的一部分）并且您的 DoctorLoaderService 取决于您的 ReviewService，因此您需要在模块和每个受影响班级的服务。在这种情况下，DocotrModule 需要 forwardRef(() => BookingModule) 和 BookingModule 需要 forwardRef(() => DoctorModule) 以及 ReviewService 和 DoctorLoadingService 具有类似的 @Inject(forwardRef(() => ) 设置。

一般来说，最好避免这些循环依赖，因为它们会造成难以调试的麻烦。也许看看是否可以改变架构，使代码更简单/更少依赖其他部分。