Update List of objects that is dependent on two other API responses with RxJava

Question

So, basically I have a list of objects that need to be updated. In order to update each object I need to call 2 dependent API calls that will eventually return data (in this case it is a user avatar).

This is what I am trying to do:

private Observable<List<User>> fetchFileInfo(List<User> userList) {
    return Observable.fromIterable(userList)
            .concatMap((Function<User, ObservableSource<FileData>>) user -> fetchFileInfoById(user.getId()))
            .concatMap((Function<FileData, ObservableSource<String>>) fileData -> fetchAvatarUrl(fileData.getEntityId()))
            .concatMap((Function<String, ObservableSource<User>>) avatarUrl -> ???)
            .toList()
            .toObservable();
}

private Observable<FileData> fetchFileInfoById(int id) {
    return getApiService()
            .getFileInfo(id)
            .map(fileDataResponseWrapper -> fileDataResponseWrapper.getData().get(0));
}

private Observable<String> fetchAvatarUrl(int entityId) {
    return getApiService()
            .getFile(entityId)
            .map(responseBodyResponse -> responseBodyResponse.raw().request().url().toString());
}

So, first I fetch the file for each user and then I fetch the avatar for that file info. But, how do I update each of the objects with the avatar that I've received?

Answer 1

Create nested rx chain:

return Observable.fromIterable(userList)
    .concatMap(user -> {
        return fetchFileInfoById(user.getId())
            .concatMap(fileData -> fetchAvatarUrl(fileData.getEntityId()))
            .concatMap(avatarUrl -> getUpdatedUser(user, avatarUrl))
    })
    .toList()
    .toObservable();

You can reference the user instance in the inner chain.

Second option is to create wrappers like this example:

private Observable<List<User>> fetchFileInfo(List<User> userList) {
    return Observable.fromIterable(userList)
            .concatMap((Function<User, ObservableSource<Pair>>) user -> new Pair(user, fetchFileInfoById(user.getId())))
            .concatMap((Function<Pair, ObservableSource<Triple>>) pair -> new Triple(pair.user, pair.fileData, fetchAvatarUrl(pair.fileData.getEntityId())))
            .concatMap((Function<Triple, ObservableSource<User>>) triple -> getUpdatedUser(triple.user, triple.avatarUrl))
            .toList()
            .toObservable();
}



class Pair {
    User user;
    FileData fileData;
}

class Triple {
    User user;
    FileData fileData;
    String avatarUrl;
}