How to intercept the methods of service and repository and obtain the context?

[skypesky]

What's the problem?

When I use global interceptors, class level interceptors and method level interceptors, I find that I can only control the controller, not the service and repository fields.

Reproduce

loopback4 test project: https://github.com/skypesky/interceptor-test-reproduce

git clone https://github.com/skypesky/interceptor-test-reproduce
cd interceptor-test-reproduce
npm install
npm start

• UserController

export class UserController {
  constructor(
    @service()
    private userService: UserService,
  ) { }

  @get('/users/existsByUsername/${username}')
  public async existsByUsername(
    @param.path.string('username', {
      example: 'username1'
    })
    username: string
  ): Promise<boolean> {
    console.log('user controller loaded');
    return this.userService.existsByUsername(username);
  }

}

• UserService

@injectable({scope: BindingScope.TRANSIENT})
export class UserService {
  constructor(
    @repository(UserRepository)
    private userRepository: UserRepository,
  ) { }

  public async existsByUsername(username: string): Promise<boolean> {
    console.log('user service loaded');
    return this.userRepository.existsByUsername(username);
  }
}

• UserRepository

export class UserRepository extends DefaultCrudRepository<
  User,
  typeof User.prototype.username,
  UserRelations
> {
  constructor(
    @inject('datasources.Test') dataSource: TestDataSource,
  ) {
    super(User, dataSource);
  }

  public async existsByUsername(username: string): Promise<boolean> {
    console.log('user repository loaded');
    if (!(await this.exists(username))) {
      await this.create(new User({
        username,
        password: '123456',
      }));
    }
    return this.exists(username);
  }
}

The expected behaviour

call: http://localhost:3000/explorer/#/UserController/UserController.existsByUsername

UserController#existsByUsername() interceptor success!
user controller loaded
UserService#existsByUsername() interceptor success!
user service loaded
UserRepository#existsByUsername() interceptor success!
user repository loaded

Actual result

call: http://localhost:3000/explorer/#/UserController/UserController.existsByUsername

UserController#existsByUsername() interceptor success!
user controller loaded
user service loaded
user repository loaded