Combine scan with network request to update model in RxSwift - reactive-programming

Question

Currently I'm having a Observable created using scan to update underlying model using a PublishSubject like this:
class ViewModel {
private enum Action {
case updateName(String)
}
private let product: Observable<Product>
private let actions = PublishSubject<Action>()
init(initialProduct: Product) {
product = actions
.scan(initialProduct, accumulator: { (oldProduct, action) -> Product in
var newProduct = oldProduct
switch action {
case .updateName(let name):
newProduct.name = name
}
return newProduct
})
.startWith(initialProduct)
.share()
}
func updateProductName(_ name: String) {
actions.onNext(.updateName(name))
}
private func getProductDetail() {
/// This will call a network request
}
}
Every "local" actions like update product's name, prices... is done by using method like updateProductName(_ name: String) above. But what if I want to have a network request that also update the product, and can be called every time I want, for example after a button tap, or after calling updateProductName?
// UPDATE: After read iWheelBuy's comment and Daniel's answer, I ended up using 2 more actions
class ViewModel {
private enum Action {
case getDetail
case updateProduct(Product)
}
///....
init(initialProduct: Product) {
product = actions
.scan(initialProduct, accumulator: { (oldProduct, action) -> Product in
var newProduct = oldProduct
switch action {
case .updateName(let name):
newProduct.name = name
case .getDetail:
self.getProductDetail()
case .updateProduct(let p):
return p
}
return newProduct
})
.startWith(initialProduct)
.share()
}
func getProductDetail() {
actions.onNext(.getDetail)
}
private func getProductDetail(id: Int) {
ProductService.getProductDetail(id) { product in
self.actions.onNext(.updateProduct(product))
}
}
}
But I feel that, I trigger side effect (call network request) inside scan, without updating the model, is that something wrong?
Also how can I use a "rx" network request?
// What if I want to use this method instead of the one above,
// without subscribe inside viewmodel?
private func rxGetProductDetail(id: Int) -> Observable<Product> {
return ProductService.rxGetProductDetail(id: Int)
}

Answer 1

I'm not sure why #iWheelBuy didn't make a real answer because their comment is the correct answer. Given the hybrid approach to Rx in your question, I expect something like the below will accommodate your style:
class ViewModel {
private enum Action {
case updateName(String)
case updateProduct(Product)
}
private let product: Observable<Product>
private let actions = PublishSubject<Action>()
private var disposable: Disposable?
init(initialProduct: Product) {
product = actions
.scan(initialProduct, accumulator: { (oldProduct, action) -> Product in
var newProduct = oldProduct
switch action {
case .updateName(let name):
newProduct.name = name
case .updateProduct(let product):
newProduct = product
}
return newProduct
})
.startWith(initialProduct)
.share()
// without a subscribe, none of this matters. I assume you just didn't show all your code.
}
deinit {
disposable?.dispose()
}
func updateProductName(_ name: String) {
actions.onNext(.updateName(name))
}
private func getProductDetail() {
let request = URLRequest(url: URL(string: "https://foo.com")!)
disposable?.dispose()
disposable = URLSession.shared.rx.data(request: request)
.map { try JSONDecoder().decode(Product.self, from: $0) }
.map { Action.updateProduct($0) }
.subscribe(
onNext: { [actions] in actions.onNext($0) },
onError: { error in /* handle error */ }
)
}
}
The style above is still pretty imperative but if you don't want your use of Rx to leak out of the view model it's okay.
If you want to see a "full Rx" setup, you might find my sample repo interesting: https://github.com/danielt1263/RxEarthquake
UPDATE
But I feel that, I trigger side effect (call network request) inside scan, without updating the model, is that something wrong?
The scan function should be pure with no side effects. Calling a network request inside it's closure is inappropriate.