NestJS Cannot resolve dependencies of the UsersModule

问题

NestJS Cannot resolve dependencies of the UsersModule. Error: Error: Nest can't resolve dependencies of the UsersModule (?). Please verify whether [0] argument is available in the current context.

app.module.ts:

@Module({
  imports: [
    ConfigModule,
    DatabaseModule,
    GraphQLModule,
    UsersModule,
  ],
  providers: [
    ErrorService,
  ],
  exports: [
    DatabaseModule,
    ErrorService,
  ],
})
export class AppModule implements NestModule {}

users.module.ts:

@Module({
    imports: [
        DatabaseModule,
        ErrorService,
    ],
    providers: [
        UsersService,
        ...usersProviders,
        UserResolver,
    ],
})
export class UsersModule {
    constructor(private readonly errorService: ErrorService) {}
}

Problem is this ErrorService, but for instance Database module is used in similar way, and it works without any error. I'm little confused) Maybe somebody would help. Thank you.

回答1:

ErrorService is not properly injected in UsersModule.

It should either be:

In the providers of UsersModule
In the exports of one module imported by UsersModule

Otherwise, Nest won't be able to resolve it. And adding it to the exports of AppModule doesn't make it globally available, either.

I can see three solutions:

1 - Adding ErrorService to the providers of UsersModule. But it doesn't look a proper way, as I think/guess that you will reuse this service in many other parts of the code (right?). Thus, better:
2 - Create a ErrorsModule which exports the ErrorService, then UsersModule will import ErrorsModule and will be able to inject the service.

Like:

// errors.module.ts
@Module({
  providers: [ ErrorService ],
  exports: [ ErrorService ],
})
export class ErrorsModule {}

// users.module.ts
@Module({
  imports: [ErrorsModule],
})
export class UsersModule {
  constructor(private readonly errorService: ErrorService) {}
}

3 - My favorite, if your service is supposed to be reused (would LoggerService be a better name? If my guess is correct), use a @Global module that you'll import only once in your main module (AppModule)

Example:

@Global()
@Module({
  providers: [LoggerService],
  exports: [LoggerService],
})
export class LoggerModule {
  constructor(private readonly loggerService: LoggerService) { /* initialize logger, or whatever */ }
}

Then you must add LoggerModule to the imports of AppModule, and LoggerService will be injectable anywhere without having to re-declare it.

来源：https://stackoverflow.com/questions/50822301/nestjs-cannot-resolve-dependencies-of-the-usersmodule

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typescript

nestjs