How to return variable from observable into another observable type

Kali Aney :

I query the youtube api and made several models to map the json with gson converter. Now I want to use repository pattern and unify the return value from my database and from remote, but I have some issues to know how to return a specific variable from an observable in RxJava.

I query the api like this:

@GET("playlistItems?part=snippet")
fun getLatestVideosFromPlaylist(@Query("playlistId") playlistId:String, @Query("maxResults") maxResults:String): Observable<YoutubeVideosModel>

My models

data class YoutubeVideosModel(
    @SerializedName("items")
    val videos: ArrayList<YoutubeVideo>
)

@Entity(tableName = "video")
data class YoutubeVideo(
    @PrimaryKey(autoGenerate = true)
    val id: Int? = null,

    @SerializedName("snippet")
    val video: YoutubeVideoData
)

My data source interface

interface VideoDataSource {
   fun fetchVideos(playlistId:String) : Observable<ArrayList<YoutubeVideo>>
}

From my local data source I return a arrayList of youtubeVideo

object VideoLocalSource: VideoDataSource {

override fun fetchVideos(playlistId: String): Observable<ArrayList<YoutubeVideo>> {
    return Observable.fromCallable {
        AppDatabase.getInstance(BaseApp.INSTANCE)?.getVideoDao()!!.fetchAllVideos()
    }
  }
}

But from my remote I cannot find how to return the same:

object VideoRemoteSource: VideoDataSource {

override fun fetchVideos(playlistId: String, maxResults:String): Observable<ArrayList<YoutubeVideo>> {

    YoutubeApiClient.getYoutubeService().getLatestVideosFromPlaylist(playlistId, maxResults)
            .subscribe {
                videoModel ->
                //Here cannot use return
                return ObservableFromArray(arrayOf(videoModel.videos)
            }
      }
}

talhature :

What you are having difficulty with is the way asynchronous programming requires you to think. Returning an observable inside a subscription callback is not valid. Because you don't know when the subscriber will be called

For a case like this where you want to return an observable of what you are fetching asynchronously, you can use a map like below.

object VideoRemoteSource: VideoDataSource {

override fun fetchVideos(playlistId: String, maxResults:String): Observable<ArrayList<YoutubeVideo>> {

    return YoutubeApiClient.getYoutubeService().getLatestVideosFromPlaylist(playlistId, maxResults)
    .map(videoModel -> arrayOf(videoModel.videos));
}