class User: VettyProtocol { // <--- STEP1: Inherit VettyProtocol
    
    var uniqueKey: VettyIdentifier {
        return userId // <--- STEP2: return model uniqueKey
    }
    
    var userId: Int = -1
    var username: String = ""
    var profileURL: URL?
    
    enum CodingKeys: String, CodingKey {
        case userId = "id"
        case username = "login"
        case profileURL = "avatar_url"
    }
    
    func commitSubModelIfNeeds() { // <---- STEP3: (Optional) 
        // Will pass, user model doen't has VettyProtocol Sub-Model
    }
}

let userIdForVetty: VettyIdentifier = Vetty.shared.commit(user)

let userIdForVettyObservable: Observable<VettyIdentifier> =
  Observable.just(user)
            .asObservable()
            .map({ $0.map({ $0 as VettyProtocol }) })
            .commits(ignoreSubModel: false)

let user: User? = Vetty.shared.read(type: User.self, uniqueKey: 12345)

let userObservable: Observable<User?> = Vetty.rx.observer(type: User.self, uniqueKey: 12345)

guard let user = Vetty.shared.read(type: User.self, uniqueKey: 12345) else { return }
user.profileURL = URL(string: "https://avatars1.githubusercontent.com/u/19504988?s=460&v=4")
Vetty.shared.commit(user, ignoreSubModel: true)

let observable: Observable<User?> = Vetty.rx.observer(type: User.self, uniqueKey: 12345)
Observable.just(URL(string: "https://avatars1.githubusercontent.com/u/19504988?s=460&v=4"))
          .mutate(with: observable,
                  { user, newURL -> User? in
                      user?.profileURL = newURL
                      return user
            })
            .disposed(by: disposeBag)

let repoObservable = Vetty.rx.observer(type: Repository.self, uniqueKey: repoId)
        
let userObservable = repoObservable
            .filterNil()
            .map { $0.user?.uniqueKey }
            .asObserver(type: User.self)

let observable: Observable<User?> = Vetty.rx.observer(type: User.self, uniqueKey: 12345)
Observable.just(URL(string: "https://avatars1.githubusercontent.com/u/19504988?s=460&v=4"))
          .mutate(with: observable,
                  ignoreSubModel: true) <--- Default is true!
                  { user, newURL -> User? in
                      user?.profileURL = newURL
                      return user
            })
            .disposed(by: disposeBag)

class Repository: VettyProtocol {
    
    var uniqueKey: VettyIdentifier {
        return id
    }
    
    var id: Int = -1
    var user: User?
    var repositoryName: String?
    var desc: String?
    var isPrivate: Bool = false
    var isForked: Bool = false
    
    enum CodingKeys: String, CodingKey {
        case id = "id"
        case user = "owner"
        case repositoryName = "full_name"
        case desc = "description"
        case isPrivate = "private"
        case isForked = "fork"
    }
    
    func commitSubModelIfNeeds() {
        
        Vetty.shared.commitIfNeeds(user)
    }
}

class User: VettyProtocol {
    
    var uniqueKey: VettyIdentifier {
        return userId
    }
    
    var userId: Int = -1
    var username: String = ""
    var profileURL: URL?
    
    enum CodingKeys: String, CodingKey {
        case userId = "id"
        case username = "login"
        case profileURL = "avatar_url"
    }
    
    func commitSubModelIfNeeds() {
        
    }
}

let observable: Observable<Repository?> = Vetty.rx.observer(type: Repository.self, uniqueKey: "repo-23")
Observable.just("New Repository Description")
          .mutate(with: observable,
                  ignoreSubModel: false) 
                  { repo, newDesc -> Repository? in
                      
                      if let userId = repo.user?.userId, 
                      let latestUser = Vetty.shared.read(type: User.self, uniqueKey: userId) {
                        repo.user = latestUser
                      }
                      
                      repo?.desc = newDesc
                      return repo
            })
            .disposed(by: disposeBag)