Multiple POST requests with RxJava - kotlin

Question

I have a list of Books.
open class Book(
#PrimaryKey
var id: String? = null,
var title: String? = null,
var author: String? = null
): RealmObject()
While for-looping, I filter some books and create an Observable with filtered ones. I add each observable to an array.
val listInserts = ArrayList<Observable<Book>>()
for loop(..) {
if (localBook condition) {
val postObservable = networkApiAdapter.insert(localBook)
listInserts.add(postObservable)
}
}
I merge (or concat) the observables hoping for some sequential POST requests.
Observable.concat(listInserts)
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(
{ s ->
println(s)
},
{ err ->
println(err)
},
{ println("onComplete") }
)
Always only one POST request is received at my MongoDb+Flask server and I also get this error:
com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected BEGIN_OBJECT but was NUMBER at line 1 column 4 path $
networkApiAdapter functions, Retrofit:
class NetworkAPIAdapter private constructor() {
fun insert(dto: Book): Observable<Book> {
println(dto.toString())
return bookService.insert(dto.title!!, dto.author!!)
}
interface BooksService {
#FormUrlEncoded
#POST(URL_ORDERS_ALL)
fun insert(
#Field("title") title: String,
#Field("author") author: String
): Observable<Book>
}
}
Any help would be welcomed. I don't know how to do multiples requests. I have tried many solutions with zip, repeatUntil, flatMap, but none worked.
After solving this, I have to delete all local books and do a GET request. All somehow working using RxJava.

Answer 1

Your BooksService.insert is defined as a POST request that expects a response from server in form of a Book JSON string (i.e. Observable<Book>). I think that is not what your server returns after the POST request goes through. Check what your POST request returns, I think it returns some Int (probably a response status) instead of a Book, which would explain your error:
com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected BEGIN_OBJECT but was NUMBER at line 1 column 4 path $
If that is the case, your concatenated Observable will terminate as soon as the error is thrown, i.e. right after your first POST request, therefore the remaining requests will not be executed.
If my assumptions were right, change your service to:
interface BooksService {
#FormUrlEncoded
#POST(URL_ORDERS_ALL)
fun insert(
#Field("title") title: String,
#Field("author") author: String
): Observable<Int>
}
Also, if you want your other requests to execute even if the previous throws an error, do:
val postObservable = networkApiAdapter.insert(localBook).onErrorReturn(_ -> SOME_INT_FLAG)
UPDATE
To execute your required logic after all the POST requests have been sent, try:
Observable.concat(listInserts)
// complete this observable after all POST requests have been sent
// not that it does not necesarily mean that all responses were 200, you should implement yourself what happens to items that were not successfully `POST`ed
.take(listInserts.size)
.doOnComplete {
// called when this observable completes, i.e. when all POST requests have been sent
executeFinalActions()
}
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(
{ s->
println(s)
},
{ err ->
println(err)
},
{ println("onComplete") }
)
And implement the executeFinalActions() function:
private fun executeFinalActions() {
realm.executeTransaction(Realm::deleteAll)
networkApiAdapter.fetchAll()
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(
{ books ->
// todo: store books
},
{ err ->
println(err)
}
)
}
PS: you may want to have a look what Observable.take() does: http://reactivex.io/documentation/operators/take.html