RxSwift and MVVM: observable not executing without binding - swift

Question

I'm new to RxSwift and trying implement app that using MVVM architecture. I have view model:
class CategoriesViewModel {
fileprivate let api: APIService
fileprivate let database: DatabaseService
let categories: Results<Category>
// Input
let actionRequest = PublishSubject<Void>()
// Output
let changeset: Observable<(AnyRealmCollection<Category>, RealmChangeset?)>
let apiSuccess: Observable<Void>
let apiFailure: Observable<Error>
init(api: APIService, database: DatabaseService) {
self.api = api
self.database = database
categories = database.realm.objects(Category.self).sorted(byKeyPath: Category.KeyPath.name)
changeset = Observable.changeset(from: categories)
let requestResult = actionRequest
.flatMapLatest { [weak api] _ -> Observable<Event<[Category]>> in
guard let strongAPI = api else {
return Observable.empty()
}
let request = APIService.MappableRequest(Category.self, resource: .categories)
return strongAPI.mappedArrayObservable(from: request).materialize()
}
.shareReplayLatestWhileConnected()
apiSuccess = requestResult
.map { $0.element }
.filterNil()
.flatMapLatest { [weak database] newObjects -> Observable<Void> in
guard let strongDatabase = database else {
return Observable.empty()
}
return strongDatabase.updateObservable(with: newObjects)
}
apiFailure = requestResult
.map { $0.error }
.filterNil()
}
}
and I have following binginds in view controller:
viewModel.apiSuccess
.map { _ in false }
.bind(to: refreshControl.rx.isRefreshing)
.disposed(by: disposeBag)
viewModel.apiFailure
.map { _ in false }
.bind(to: refreshControl.rx.isRefreshing)
.disposed(by: disposeBag)
But if I comment bindings, part with database updating stops executing. I need to make it execute anyway, without using dispose bag in the view model. Is it possible?
And little additional question: should I use weak-strong dance with api/database and return Observable.empty() like in my view model code or can I just use unowned api/unowned database safely?
Thanks.
UPD:
Function for return observable in APIService:
func mappedArrayObservable<T>(from request: MappableRequest<T>) -> Observable<[T]> {
let jsonArray = SessionManager.jsonArrayObservable(with: request.urlRequest, isSecured: request.isSecured)
return jsonArray.mapResponse(on: mappingSheduler, { Mapper<T>().mapArray(JSONArray: $0) })
}

Answer 1

Work doesn't get done unless there is a subscriber prepared to receive the results.
Your DatabaseService needs to have a dispose bag in it and subscribe to the Observable<[Category]>. Something like:
class ProductionDatabase: DatabaseService {
var categoriesUpdated: Observable<Void> { return _categories }
func updateObservable(with categories: Observable<[Category]>) {
categories
.subscribe(onNext: { [weak self] categories in
// store categories an then
self?._categories.onNext()
})
.disposed(by: bag)
}
private let _categories = PublishSubject<Void>()
private let bag = DisposeBag()
}
Then apiSuccess = database.categoriesUpdated and database.updateObservable(with: requestResult.map { $0.element }.filterNil())