How to concatEagerDelayError in RxJava2 - rx-java2

Question

How to implement a Observable.concatEagerDelayError or an equivalent in RxJava2/RxKotlin2 ?
There is :
Observable.concatEager
Observable.concatDelayError
But not :
Observable.concatEagerDelayError
What i have :
fun getAll(): Observable<List<User>> = Observable.concatArrayDelayError(
// from db
userDAO
.selectAll()
.subscribeOn(ioScheduler),
// from api
userAPI
.getAll()
.doOnNext { lstUser -> Completable.concatArray(
userDAO.deleteAll().subscribeOn(ioScheduler),
userDAO.save(lstUser).subscribeOn(ioScheduler)
) }
.subscribeOn(ioScheduler)
)
I want same behaviour but eagerly for selectAll() and getAll() because there is no reason to wait from db to launch network call.

Answer 1

Use concatMapEagerDelayError:
Observable.fromIterable(sources)
.concatMapEagerDelayError(v -> v, true);
Observable.fromArray(source1, source2, source3)
.concatMapEagerDelayError(v -> v, true);
JavaDoc.
Edit:
fun getAll(): Observable<List<User>> = Observable.fromArray(
// from db
userDAO
.selectAll()
.subscribeOn(ioScheduler),
// from api
userAPI
.getAll()
// --- this makes no sense by the way -------------------
.doOnNext { lstUser -> Completable.concatArray(
userDAO.deleteAll().subscribeOn(ioScheduler),
userDAO.save(lstUser).subscribeOn(ioScheduler)
)}
// ------------------------------------------------------
.subscribeOn(ioScheduler)
)
.concatMapEagerDelayError({ v -> v }, true)