Rxjava: How to chain calls, depending on result ?

[thierryler]

Hello,

In my webapp, I have to chain two async calls :
The first call gives me a list of dog ids.
The second call gives me a Dog (found by its id).

In my code, i'd like to write something like :

final Observable<RxMessage<String>> observable1 = asyncCallForDogIds(..);

final List<Dog> dogs = new ArrayList<>();
observable1.subscribe(
    // onNext
    (RxMessage<String> message) -> {
        final String id = readId(message);

        final Observable<RxMessage<String>> observable2 = someAsyncCallForOneDogId(id, ..);

        final Dog dog = readFromSomeMessage2(...);
        dogs.add(dog);
    },

    // onError
    (Throwable err) -> error(err, ..),

    // onCompleted
    () -> resume(dogs, ..));

What would be the best way to do that ?
Th.

[hamidp]

You want flatMap so roughly:

asyncCallForDogIds(..)
    .map(this::readId)
    .flatMap(dogId -> someAsyncCallForOneDogId(id, ..))
    .map(this::readFromSomeMessage2)

[thierryler]

Yes that looks what I need. Thx. But how do I process the onError and onCompleted ? for each async call

[hamidp]

Those will propagate down the chain. If any Observable emits an error it will be sent down to your subscriber.

[benjchristensen]

If you want to handle errors for each call you put the onErrorResumeNext or similar handlers on each of the async calls.

asyncCallForDogIds(..)
    .map(this::readId)
    .flatMap(dogId -> {
             return someAsyncCallForOneDogId(id, ..)
                             .onErrorResumeNext(errorHandlingHere)
    })
    .map(this::readFromSomeMessage2)

[thierryler]

Thx for those great answers.

I'm getting a little confused. What about if my first call returns an object that contains many ids, and I have to process the second call for each id :

I was thinking about something like this :

final Observable<RxMessage<String>> observable1 = doCallThatReturnBoxes(userId);

Box box = null;
observable1
    .flatMap(new Func1<RxMessage<String>, Observable<RxMessage<String>>>() 
        public Observable<RxMessage<String>> call(RxMessage<String> message) {
            box = readBoxFromMessage(message);

            final List<String> ids = box.getItemIds();

            // Here I need to call doCallThatReturnOneItemDetails for each id
            // How do I create an Observable from the ids list ?

        }
        .subscribe(
            // onNext
            (RxMessage<String> message) -> {
                final BoxItem boxItem = readBoxItemFromMessage(message);

                box.getItems.add(boxItem);
            },

            // onError
            (Throwable err) -> error(err, response, resp),

            // onCompleted
            () -> resume(response, resp)
        );

And if my first call returns a list of boxies ? like this ?

final List<Box> boxies = new ArrayList<>();
observable1
    .flatMap(new Func1<RxMessage<String>, Observable<RxMessage<String>>>() 
        public Observable<RxMessage<String>> call(RxMessage<String> message) {
            final Box box = readBoxFromMessage(message);
            boxies.add(box);

            final List<String> ids = box.getItemIds();

            // Here I need to call doCallThatReturnOneItemDetails for each id
            // How do I create an Observable from the ids list ?

        }
        .subscribe(
            // onNext
            (RxMessage<String> message) -> {
                final BoxItem boxItem = readBoxItemFromMessage(message);

                // Here how to specify the good box ?
                box.getItems.add(boxItem);
            },

            // onError
            (Throwable err) -> error(err, response, resp),

            // onCompleted
            () -> resume(response, resp)
        );

How do I associate the item details with the good box ?

[akarnokd]

I'm closing this due to inactivity. If you have further questions, please don't hesitate to reopen this issue or post a new one.