I have to beg people here who might have an elegan...

# rx

[Nikola Milovic]

I have to beg people here who might have an elegant solution to this callback hell..

https://stackoverflow.com/questions/60431813/combining-multiple-firebase-callbacks-with-rxjava2

[kioba]

it’s not hell, you just trying to burn the forest around yourself. 🔥 give me a couple of minutes and I take a look

[kioba]

first mistake: loadDrillTypes if the stream fails it closes we can’t iterate on the documents any more. We need to move the loop insude the try:

fun loadDrillTypes(): Observable<DrillsType> = 
  Observable.create<DrillsType> { emitter ->
    firebaseFirestore.collection("drilltypes")
      .get()
      .addOnSuccessListener { documents ->
        try {
          for (document in documents) {
            val doc = document.toObject(DrillsType::class.java)
            emitter.onNext(doc)
          }
        } catch (e: Exception) {
          emitter.onError(e)
        }
          emitter.onComplete()
      }
      .addOnFailureListener { exception ->
          Log.w("TAG", "Error getting documents: ", exception)
          emitter.onError(exception)
      }
  }

[kioba]

You sould use flatmap:

remoteDataSource
  .loadDrillTypes()
  .flatMap { data ->
    getImageUrl(data.drillType_imageUrl)
      .map{ 
         data.copy(drillType_imageUrl = it)
       }
  }

[Nikola Milovic]

@kioba thanks for giving me these pointers! It seems so much more elegant. Can you elaborate on the second part with the flatmap? I've looked into it but cannot get it to work. And honestly don't quite get how this works the way it should.

[Matej Drobnič]

I've answered you on the SO

[pg]

You can also check how was it done by other people, for instance this little Rx Firebase wrapper lib. Maybe you will be inspired 😆 https://github.com/FrangSierra/RxFirebase

[Nikola Milovic]

Thank you guys! This was the winning solution

fun loadFullDrillType(): Observable<DrillsType> {
        return loadDrillTypeWithRawImageUrl().flatMapSingle { rawImageUrl ->
            loadImageUrl(rawImageUrl.drillType_imageUrl).map {
                return@map rawImageUrl.copy(drillType_imageUrl = it)
            }
        }
    }

Also used your @kioba try and catch fix for callbacks and documents.
Thanks everyone ❤️
Didn't know that there was such a concise and simple solution to this problem.

[Nikola Milovic]

@Matej Drobnič Just a quick note, how do you throw exceptions this way? It seems that if the datasources emit error it doesn't get pushed to the top. But rather nothing happens.

[Matej Drobnič]

If the wrapper is implemented properly, then all exceptions should propagate up the stack normally and end up in onError method of original subscriber