Am I using firebase api incorrectly? - swift

Question

Whenever paging in tableview, the view model is running fetchDataRx. It works well, but I don't think it's right to sort the entire data every time you paginate and call the addSnapShotListener. If my code is not correct, how can I correct it?
// MARK: ViewController.swift
timeLineTableView.rx.didScroll
.withLatestFrom(viewModel.activated)
.subscribe(onNext: { [weak self] isActivated in
if !isActivated {
guard let self = self else { return }
let position = self.timeLineTableView.contentOffset.y
if position > self.timeLineTableView.contentSize.height - 100 - self.timeLineTableView.frame.size.height {
self.viewModel.fetchPosts.onNext(())
}
}
})
.disposed(by: disposeBag)
//MARK: ViewModel.swift
let fetchPosts: AnyObserver<Void>
let fetching = PublishSubject<Void>()
fetchPosts = fetching.asObserver()
fetching
.do(onNext: { _ in activating.onNext(true) })
.withLatestFrom(posts)
.map { $0.count }
.flatMap{ (count) -> Observable<[post]> in
fireBaseService.fetchDataRx(startIdx: count) }
.map { $0.map { ViewPost(post: $0) } }
.do(onNext: { _ in activating.onNext(false) })
.do(onError: { err in error.onNext(err) })
.subscribe(onNext: { newPosts in
let oldData = posts.value
posts.accept(oldData + newPosts)
})
.disposed(by: disposeBag)
//MARK: FirebaseService.swift
protocol FirebaseServiceProtocol {
func fetchDataRx(startIdx: Int) -> Observable<[post]>
func fetchData(startIdx: Int, completion: #escaping (Result<[post], Error>) -> Void)
}
class FireBaseService: FirebaseServiceProtocol {
func fetchDataRx(startIdx: Int) -> Observable<[post]> {
return Observable.create { (observer) -> Disposable in
self.fetchData(startIdx: startIdx) { result in
switch result {
case .success(let data):
observer.onNext(data)
case .failure(let error):
observer.onError(error)
}
observer.onCompleted()
}
return Disposables.create()
}
}
func fetchData(startIdx: Int, completion: #escaping (Result<[post], Error>) -> Void) {
let db = Firestore.firestore()
let formatter = DateFormatter()
formatter.dateFormat = "yyyy-MM-dd HH:mm"
if startIdx == 0 {
DispatchQueue.global().async {
let first = db.collection("lolCourt")
.order(by: "date")
.limit(to: 8)
var nextPosts = [post]()
first.getDocuments() { (querySnapshot, error) in
if let error = error {
print("Error getting documents: \(error)")
} else {
for document in querySnapshot!.documents {
guard let url = document.data()["url"] as? String else {
continue
}
guard let champion1 = document.data()["champion1"] as? String else {
continue
}
guard let champion1Votes = document.data()["champion1Votes"] as? Double else {
continue
}
guard let champion2 = document.data()["champion2"] as? String else {
continue
}
guard let champion2Votes = document.data()["champion2Votes"] as? Double else {
continue
}
guard let text = document.data()["text"] as? String else {
continue
}
guard let date = document.data()["date"] as? Double else {
continue
}
nextPosts.append(post(url: url,
champion1: champion1,
champion1Votes: champion1Votes,
champion2: champion2,
champion2Votes: champion2Votes,
text: text,
date: formatter.string(from: Date(timeIntervalSince1970: date))))
}
}
completion(.success(nextPosts))
}
}
}
else {
DispatchQueue.global().async {
let first = db.collection("lolCourt")
.order(by: "date")
.limit(to: startIdx)
first.addSnapshotListener { (snapshot, error) in
guard let snapshot = snapshot else {
print("Error retrieving : \(error.debugDescription)")
return
}
guard let lastSnapshot = snapshot.documents.last else {
return
}
let next = db.collection("lolCourt")
.order(by: "date")
.start(afterDocument: lastSnapshot)
.limit(to: 8)
var nextPosts = [post]()
next.getDocuments() { (querySnapshot, error) in
if let error = error {
print("Error getting documents: \(error)")
} else {
for document in querySnapshot!.documents {
guard let url = document.data()["url"] as? String else {
continue
}
guard let champion1 = document.data()["champion1"] as? String else {
continue
}
guard let champion1Votes = document.data()["champion1Votes"] as? Double else {
continue
}
guard let champion2 = document.data()["champion2"] as? String else {
continue
}
guard let champion2Votes = document.data()["champion2Votes"] as? Double else {
continue
}
guard let text = document.data()["text"] as? String else {
continue
}
guard let date = document.data()["date"] as? Double else {
continue
}
nextPosts.append(post(url: url,
champion1: champion1,
champion1Votes: champion1Votes,
champion2: champion2,
champion2Votes: champion2Votes,
text: text,
date: formatter.string(from: Date(timeIntervalSince1970: date))))
}
}
completion(.success(nextPosts))
}
}
}
}
}
}

Answer 1

I think you are doing it wrong... I would expect to see something more like this:
class FireBaseService {
func getPage<T>(query: Query? = nil, build: #escaping ([String: Any]) -> T) -> Observable<([T], nextPage: Query?)> {
Observable.create { observer in
let db = Firestore.firestore()
let page = query ?? db.collection("lolCourt")
.order(by: "date")
.limit(to: 8)
let listener = page
.addSnapshotListener { snapshot, error in
guard let snapshot = snapshot else { observer.onError(error ?? RxError.unknown); return }
let items = snapshot.documents.map { build($0.data()) }
if let lastSnapshot = snapshot.documents.last {
let next = page
.start(afterDocument: lastSnapshot)
observer.onSuccess((items, nextPage: next))
}
else {
observer.onSuccess((items, nextPage: nil))
}
}
return Disposables.create { listener.remove() }
}
}
}
Use the above in your favorite state machine system. Here is an example using my CLE library.
// in view controller
let fireBaseService = FireBaseService()
let activityIndicator = ActivityIndicator()
let errorRouter = ErrorRouter()
func getPage(nextPage: Query?) -> Observable<([Post?], nextPage: Query?)> {
fireBaseService.getPage(query: nextPage, build: Post.init(dict:))
.rerouteError(errorRouter)
.trackActivity(activityIndicator)
}
let posts = cycle(
inputs: [
getPage(nextPage: nil).map(ViewModel.Input.response),
timeLineTableView.rx.reachedBottom(offset: 20).map(to: ViewModel.Input.next)
],
initialState: ([Post?](), nextPage: Query?.none),
environment: getPage(nextPage:),
reduce: ViewModel.reduce(state:input:getPage:)
)
.map { $0.0.compactMap { $0 } }
and the view model:
enum ViewModel {
enum Input {
case response([Post?], nextPage: Query?)
case next
}
static func reduce(state: inout ([Post?], nextPage: Query?), input: Input, getPage: #escaping (Query) -> Observable<([Post?], nextPage: Query?)>) -> Observable<Input> {
switch input {
case let .response(posts, nextPage):
state.0 += posts
state.nextPage = nextPage
case .next:
guard let nextPage = state.nextPage else { break }
return getPage(nextPage)
.map(Input.response)
}
return .empty()
}
}