Can't understand modules. Service imports don't work.

I get that I should ask on StackOverflow, but it’s a weird place where none of my questions ever get answered, aside from myself.

The documentation is lacking for someone like me, mentally challenged.

I cannot get any of this to work either… app.module.ts

@Module({
  imports: [
    HttpModule,
    AuthenticationModule,
    UserModule,
  ],
  controllers: [AppController],
})
export class AppModule {}

user.module.ts

@Module({
  providers: [UserService],
  exports: [UserService],
})
export class UserModule {}

auth.module.ts

@Module({
  imports: [
    HttpModule,
    UserModule,
    PassportModule,
    JwtModule.register({ secret: process.env.JWT_SECRET }),
  ],
  providers: [AuthenticationService, LocalStrategy],
  controllers: [AuthenticationController],
  exports: [AuthenticationService],
})
export class AuthenticationModule {}

auth.service.ts

@Injectable()
export class AuthenticationService implements IAuthenticationService {

  constructor(
    protected readonly userService: IUserService,
    protected readonly jwtService: JwtService,
  ) {}


  /**
   * Attempts to authenticate a user with a given email and password combination.
   * 
   * @param email 
   * @param password 
   */
  public async authenticate(email: string, password: string): Promise<Session> {
    try {
      const user = await this.userService.getAuthenticationDetails(email);

      if (isNil(user)) {
        throw new Error(NOT_FOUND_ERR);
      }

      if (!comparePassword(password, user.password, user.salt)) {
        throw new Error(MISMATCH_ERR);
      }

      return sessionFactory(user._id.toString(), user.email, user.userType);
    } catch (err) {
      throw err;
    } 
  }

  /**
   * Creates a JWT from a session
   * 
   * @param session Session object to produce the JWT out of
   */
  public signJWT(session: ISession): string {
    return this.jwtService.sign(session);
  }
}

Now, when I try to run npm start I get this:

Nest can't resolve dependencies of the AuthenticationService (?, JwtService). Please make sure that the argument at index [0] is available in the AuthenticationModule context. +16ms

The docs say that I just need to import the module. Yet nothing is working. So are the docs wrong? What do I do here? Do I need to set authentication module providers to have UserService in there? If so, what’s the point of modules in that case if I can dump EVERYTHING into the main app.module.ts instead? Because this seems to be way easier.

Edit:

is the auth.module.ts supposed to look like this then?

@Module({
  imports: [
    HttpModule,
    UserModule,
    PassportModule,
    JwtModule.register({ secret: process.env.JWT_SECRET }),
  ],
  // Added User Service bellow at index [1]
  providers: [AuthenticationService, UserService, LocalStrategy],
  controllers: [AuthenticationController],
  exports: [AuthenticationService],
})
export class AuthenticationModule {}

Doesn’t it beat the purpose of modules?

Edit 2:

Well that didn’t work.

[BrunnerLivio]

@TheImpressionist more on the interface vs class thing.

From the docs:

We could determine the DTO schema by using TypeScript interfaces, or by simple classes. Interestingly, we recommend using classes here. Why? Classes are part of the JavaScript ES6 standard, and therefore they are preserved as real entities in the compiled JavaScript. On the other hand, since TypeScript interfaces are removed during the transpilation, Nest can’t refer to them at runtime.

Plus further elaboration #1228

tl;dr: Not a Nest problem, it is a TS/JS problem because interfaces do not exist on run-time.

[DogAndHerDude]

Apparently the constructor needs to look like THIS:

  constructor(
    protected readonly userService: UserService,
    protected readonly jwtService: JwtService,
  ) {}

Instead of:

  constructor(
    protected readonly userService: IUserService,
    protected readonly jwtService: JwtService,
  ) {}

Means I cannot have interfaces in the constructor. Weird flex, but ok.