I am appending a Flux with a flatMap, but if I add additional flatMaps, only the last one gets returned.
// Here is an example of the Mono function
private Mono<MyType> appendFirstMono(Group group) {
return Mono.just(group)
.map(MyType::new)
.flatMap(g -> functionZ(group)
.map(g::setField));
}
//This works as expected
public Flux<MyType> function1() {
return returnData(id)
.thenMany(service.getData(id))
.flatMap(this::appendFirstMono);
}
//This does not and only returns the last mono (3rd)
public Flux<MyType> function1() {
return returnData(id)
.thenMany(service.getData(id))
.flatMap(this::appendFirstMono)
.flatMap(this::appendSecondMono)
.flatMap(this::appendThirdMono);
}
//I've attempted to fix with this... Doesn't work as expected.
public Flux<MyType> function1() {
return returnData(id)
.thenMany(service.getData(id))
.flatMap(x -> {
return Flux.merge(
appendFirstMono(x),
appendSecondMono(x),
appendThirdMono(x)
);
});
}
I need to process each Mono function on the flux but I can't seem to get each to execute and return properly.
You can try concat to process the mono one by one check out my example
Flux.concat(getMono(0),getMono(1),getMono(2))
.map(integer -> {
System.out.println(integer);
return integer;
})
.subscribe();
}
private Mono<Integer> getMono(Integer a) {
return Mono.just(a)
;
}
this will print 0,1,2
Related
Pretty new to project reactor here, I am struggling to put a conditional check inside my Mono stream. This part of my application is receiving an object from Kafka. Let's say the object is like this.
data class SomeEvent(val id: String, val type: String)
I have a function that handles this object like this.
fun process(someEvent: SomeEvent): Mono<String> {
val id = someEvent.id
val checkCondition = someEvent.type == "thisType"
return repoOne.getItem(id)
.map {item ->
// WHAT DO I DO HERE TO PUT A CONDITIONAL CHECK
createEntryForItem(item)
}
.flatMap {entry ->
apiService.sendEntry(entry)
}
.flatMap {
it.bodyToMono(String::class.java)
}
.flatMap {body ->
Mono.just(body)
}
}
So, what I want to do is check whether checkCondition is true and if it is, I want to call a function repoTwo.getDetails(id) that returns a Mono<Details>.
createEntryForItem returns an object of type Entry
apiService.sendEntry(entry) returns a Mono<ClientResponse>
It'd be something like this (in my mind).
fun process(someEvent: SomeEvent): Mono<String> {
val id = someEvent.id
val checkCondition = someEvent.type == "thisType"
return repoOne.getItem(id)
.map {item ->
if (checkCondition) {
repoTwo.getDetails(id).map {details ->
createEntryForItem(item, details)
}
} else {
createEntryForItem(item)
}
}
.flatMap {entry ->
apiService.sendEntry(entry)
}
.flatMap {
it.bodyToMono(String::class.java)
}
.flatMap {body ->
Mono.just(body)
}
}
But, obviously, this does not work because the expression inside the if statement is cast to Any.
How should I write it to achieve what I want to achieve?
UPDATED: The location of where I like to have the conditional check.
You should use flatMap() and not map() after getItem().
return repoOne.getItem(id)
.flatMap {item ->
if (checkCondition) {
repoTwo.getDetails(id).map {details ->
createEntryForItem(item, details)
}
} else {
Mono.just(createEntryForItem(item))
}
}
In a map{} you can transform the value. Because you want to call getDetails() (which returns a reactive type and not a value) to do that you have to use flatMap{}. And that's why you need to wrap your item in a Mono by calling Mono.just(createEntryForItem(item)) on the else branch.
Just split it to another function. Your code will be cleaner too.
repoOne.getItem(id)
.map { createEntry(it, checkCondition) }.
.flatMap.....
private fun createEntry(item, checkCondition): Item {
return if (checkCondition) {
repoTwo.getDetails(id).map { createEntryForItem(item, it) }
} else {
createEntryForItem(item)
}
}
I have 2 questions:
What difference between 'bind(onNext:' and 'subscribe(onNext:'?
struct Info {
var index: Int?
var data: String?
}
let infoData: BehaviorRelay<Info> = BehaviorRelay<Info>(value: Info())
var osInfo: Observable<String> { return self.infoData.map({ return $0.data }).distinctUntilChanged() }
osInfo.bind { (target) in
print("bind!")
}.disposed(by: self.disposeBag)
osInfo.subscribe { (target) in
print("subscribe!")
}
.disposed(by: self.disposeBag)
a has no asObservable(), but well executable. What is difference a and b?
a. var osInfo: Observable<String> { return self.infoData.map({ return $0.data }).distinctUntilChanged() }
b. var osInfo: Observable<String> { return self.infoData.asObservable().map({ return $0.data }).distinctUntilChanged() }
What difference between 'bind(onNext:' and 'subscribe(onNext:'?
If we check out implementation of bind(...) we found that it does nothing else but just uses subscribe(...) underhood and crashes in Debug with error:
/**
Subscribes an element handler to an observable sequence.
In case error occurs in debug mode, `fatalError` will be raised.
In case error occurs in release mode, `error` will be logged.
- parameter onNext: Action to invoke for each element in the observable sequence.
- returns: Subscription object used to unsubscribe from the observable sequence.
*/
public func bind(onNext: #escaping (E) -> Void) -> Disposable {
return subscribe(onNext: onNext, onError: { error in
rxFatalErrorInDebug("Binding error: \(error)")
})
}
By using bind(onNext) you can express that stream should never emit error and you interested only in item events.
So you should use subscribe(onNext:...) when you interested in error / complete / disposed events and bind(onNext...) otherwise. But since it is part of RxCocoa and not RxSwift I usually use subscribe everywhere.
a has no asObservable(), but well executable. What is difference a and b?
map(...) is function declared on ObservableType and returning new Observable
Let's start from ObservableType.
ObservableType is protocol that require only one method: subscribe(...), this allow him to create default implementation of func asObservable().
For you it means that you can create Observable from any type that conform to ObservableType.
/// Represents a push style sequence.
public protocol ObservableType : ObservableConvertibleType {
func subscribe<O: ObserverType>(_ observer: O) -> Disposable where O.E == E
}
extension ObservableType {
/// Default implementation of converting `ObservableType` to `Observable`.
public func asObservable() -> Observable<E> {
// temporary workaround
//return Observable.create(subscribe: self.subscribe)
return Observable.create { o in
return self.subscribe(o)
}
}
}
So each time you call asObservable() underhood RxSwift just creates new Observable wrapper around your stream.
And if you check source of BehaviourRelay you will find that it conform to ObservableType as well. So you can create Observable from it anytime:
public final class BehaviorRelay<Element>: ObservableType { ... }
Now lets check map function:
extension ObservableType {
/**
Projects each element of an observable sequence into a new form.
- seealso: [map operator on reactivex.io](http://reactivex.io/documentation/operators/map.html)
- parameter transform: A transform function to apply to each source element.
- returns: An observable sequence whose elements are the result of invoking the transform function on each element of source.
*/
public func map<R>(_ transform: #escaping (E) throws -> R)
-> Observable<R> {
return self.asObservable().composeMap(transform)
}
}
As expected map just call asObservable() inside and operate on new Observable.
If we "unwrap" map call we will get:
var osInfoA: Observable<String> {
return infoData
.asObservable()
.composeMap { $0.data }
.distinctUntilChanged()
}
var osInfoB: Observable<String> {
return infoData
.asObservable()
.asObservable()
.composeMap { $0.data }
.distinctUntilChanged()
}
Sure it will not compile since composeMap is internal function but you got main idea.
Calling asObservable before other operators is redundant (most operators defined on ObservableType) and just add small overhead.
with RxSwift 3.6.1 I made this extension to ObservableType to get a new token after an error request:
public extension ObservableType where E == Response {
public func retryWithToken() -> Observable<E> {
return retryWhen { error -> Observable<Response> in
return error.flatMap({ (error) -> Observable<Response> in
if let myApiError: MyApiError = error as? MyApiError {
if (myApiError == MyApiError.tokenError) {
return Session.shared.myProvider.request(.generateToken)
} else {
return Observable.error(myApiError)
}
}
return Observable.error(error)
})
}
}
}
and then I can use it:
Session.shared.myProvider.rx
.request(.mySampleRequest)
.filterSuccessfulStatusCodes()
.retryWithToken()
.subscribe { event in
....
}.disposed(by: self.disposeBag)
but with RxSwift 4.0.0 now the sequence expect a
PrimitiveSequence<SingleTrait, Response>
someone can explain to me how to do the same with RxSwift 4.0.0? I try with an extension to PrimitiveSequence but I've some compilation errors.
I believe that has nothing to do with RxSwift but is a Moya change. MoyaProvider.rx.request returns Single which is a typealias for PrimitiveSequence which is not an ObservableType.
You declare your function upon the ObservableType.
So just do asObservable() before retryWithToken()
I'm having the following simplified handler function (Spring WebFlux and the functional API using Kotlin). However, I need a hint how to detect an empty Flux and then use noContent() for 404, when the Flux is empty.
fun findByLastname(request: ServerRequest): Mono<ServerResponse> {
val lastnameOpt = request.queryParam("lastname")
val customerFlux = if (lastnameOpt.isPresent) {
service.findByLastname(lastnameOpt.get())
} else {
service.findAll()
}
// How can I detect an empty Flux and then invoke noContent() ?
return ok().body(customerFlux, Customer::class.java)
}
From a Mono:
return customerMono
.flatMap(c -> ok().body(BodyInserters.fromObject(c)))
.switchIfEmpty(notFound().build());
From a Flux:
return customerFlux
.collectList()
.flatMap(l -> {
if(l.isEmpty()) {
return notFound().build();
}
else {
return ok().body(BodyInserters.fromObject(l)));
}
});
Note that collectList buffers data in memory, so this might not be the best choice for big lists. There might be a better way to solve this.
Use Flux.hasElements() : Mono<Boolean> function:
return customerFlux.hasElements()
.flatMap {
if (it) ok().body(customerFlux)
else noContent().build()
}
In addition to the solution of Brian, if you are not want to do an empty check of the list all the time, you could create a extension function:
fun <R> Flux<R>.collectListOrEmpty(): Mono<List<R>> = this.collectList().flatMap {
val result = if (it.isEmpty()) {
Mono.empty()
} else {
Mono.just(it)
}
result
}
And call it like you do it for the Mono:
return customerFlux().collectListOrEmpty()
.switchIfEmpty(notFound().build())
.flatMap(c -> ok().body(BodyInserters.fromObject(c)))
I'm not sure why no one is talking about using the hasElements() function of Flux.java which would return a Mono.
Suppose you have a branch in your promise chain that could either return nothing or an AnyObject promise. What would you specify as the return type of the 'then' closure? For example:
func sample() -> Promise<AnyObject> {
return Promise { fulfill, reject in
fulfill(1)
}
.then { _ -> Void in
if false {
return Promise { fulfill, reject in
fulfill(0)
}
}
}
}
If I put Void as the return type for the 'then' closure I get a seg fault; if I put Promise as return type then I get an error:
missing return in a closure expected to return Promise<AnyObject>
Any suggestions?
Thanks
Based on the code sample, I see no reason to return an AnyObject. If you want to optionally return Void or an Object, then make a promise that contains an optional.
func sample() -> Promise<AnyObject?> {
return Promise { fulfill, reject in
functionForGettingObjectWithCallback() { result: AnyObject? in
fulfill(result)
}
}
}