为什么nestj不能解析依赖关系

Question

所以我有一个Nest应用程序，遇到了一个非常基本的问题。

我需要使用PlaceService中的PlaceVerificationRequestService，但如果不收到以下错误，则无法正确注入：

Nest无法解析PlaceService的依赖项(PlaceRepository、ClientService，？(。请确保索引[2]处的参数依赖项在PlaceModule上下文中可用。

我的方法是遵循与导入&将ClientService注入PlaceService，但它仍然不起作用，我不知道为什么。

这是我的密码。

放置模块.ts

@Module({
imports: [
MikroOrmModule.forFeature({
entities: [Place, Client, PlaceVerificationRequest],
}),
],
providers: [PlaceService, ClientService, PlaceVerificationRequestService],
controllers: [PlaceController],
exports: [PlaceService],
})

放置验证请求.module.ts

@Module({
imports: [
MikroOrmModule.forFeature({
entities: [PlaceVerificationRequest, Client, Place],
}),
],
providers: [PlaceVerificationRequestService, ClientService, PlaceService],
controllers: [PlaceVerificationRequestController],
exports: [PlaceVerificationRequestService],
})

place.service.ts

@Injectable()
export class PlaceService {
constructor(
@InjectRepository(Place)
private readonly placeRepo: EntityRepository<Place>,
private readonly clientService: ClientService,
private readonly reqService: PlaceVerificationRequestService,
) {}

感觉我好像错过了眼前的东西，因为它感觉很基本，但我似乎找不到。有人知道吗？感谢

Answer 1

好吧，5小时后，诀窍是…阅读文档。

Nest can't resolve dependencies of the <provider> (?). Please make sure that the argument <unknown_token> at index [<index>] is available in the <module> context.
Potential solutions:
- If <unknown_token> is a provider, is it part of the current <module>?
- If <unknown_token> is exported from a separate @Module, is that module imported within <module>?
@Module({
imports: [ /* the Module containing <unknown_token> */ ]
})

If the unknown_token above is the string dependency, you might have a circular file import. 

(必须承认他们本可以想出一个更清晰的错误信息(

所以基本上问题是PlaceService被注入PlaceVerificationRequestService，而PlaceVerificationRequest Service被注入到PlaceService，所以诀窍是使用forwardRef:

PlaceVerificationRequestService

@Inject(forwardRef(() => PlaceService))
private readonly placeService: PlaceService,

PlaceService

@Inject(forwardRef(() => PlaceVerificationRequestService))
private readonly reqService: PlaceVerificationRequestService,

Answer 2

Nest无法找到如何创建PlaceService的副本，因为您没有提供PlaceService的所有不同依赖项。

这就是为什么它问<unknown_token>是提供者吗？换句话说，PlaceService是否需要此unknown_token的副本？现在，这对我来说没有意义，所以它可能想问你的是，它需要一份位置验证请求服务的副本吗？但你写这封信的方式给了你一个令人困惑的提示，你知道，我们从中得到了我们投入的东西，所以这个错误并不令人困惑，我们只是给了它一些东西，让它给了我们一个令人混淆的提示。

你可以试着通过做这样的事情来写一个测试，例如：

import { Test } from '@nestjs/testing';
import { PlaceService } from './place/service';
import { PlaceVerificationRequestService } from './place-verification-request.service';
it('can create an instance of place service', async () => {
// Create a fake copy of the place verification request service
const fakePlaceVerificationRequestService = {
find: () => Promise.resolve([])
// add properties of the service as arguments
create: () => Promise.resolve()
};
const module = await Test.createTestingModule({
providers: [
PlaceService, 
{ 
provide: PlaceVerificationRequestService, 
useValue: fakePlaceVerificationRequestService
}
],
}).compile();
const service = module.get(PlaceService);
expect(service).toBeDefined();
});