Myujth

I have three objects (say A,B,C) and to get C I need B, and to get A, I need B. In screen I need to display a property of A together with a property of C. Even though I can get all necessary data, since I use flatMap which do not have onComplete, toList() does not get executed. Here is my code.

For every a in List I need to get c and I need to return a list of type ResultMode which includes properties of a and c.

override fun methodICall(): LiveData<MutableList<ResultModel>> 
 return mySdk
 .getAllA() //Returns Flowable<List<A>>
 .flatMap Flowable.fromIterable(it) 
 .flatMap helperMethod(it) 
 .toList() // Does not get executed as flatMap isnt completed
 .toFlowable()
 .onErrorReturn Collections.emptyList() 
 .subscribeOn(Schedulers.io())
 .to LiveDataReactiveStreams.fromPublisher(it) 
 

 private fun helperMethod(a:A): Flowable<ResultModel> 
 return mySdk
 .getB(a.propertyOne!!) // Returns Single<B>
 .flatMap mySdk.getC(it.property!!) // get C returns Single<C>
 .map 
 ResultModel(name= a.name,
 date = c.date.toString(), 
 message = it.messageId!!
 )
 .toFlowable()
 

Note: I asked a similar question earlier today but it did not require using flatmap more than once. You can view my solution to that in this link

RxJava - Mapping a result of list to another list

My Effort (Which is probably wrong)
Here is my effort of transforming first method (for second method I just remove to Flowable and return single) but it has a long way to go and I think I am in the wrong path.

 override fun methodICall(): LiveData<MutableList<ResultModel>> 
 return mySdk
 .getAllA()
 .concatMapSingle Flowable.fromIterable(it)
 .map helperMethod(it) 
 .toList()
 
 .onErrorReturn Collections.emptyList() 
 .subscribeOn(Schedulers.io())
 .to LiveDataReactiveStreams.fromPublisher(it) // here it is single. I think it is because two maps are applied both to helperMethod itself and inside helper method to result model
 

There doesn't seem to be a good reason to continually deconstruct and reconstruct lists. Assuming there isn't:

override fun methodICall(): LiveData<MutableList<ResultModel>> 
 return mySdk
 .getAllA() // Returns Flowable<List<A>>
 .flatMapIterable(it)
 .concatMapSingle( item => 
 mySdk.getB(item.propertyOfA!!)
 .flatMap( bItem => mySdk.getC( bItem.propertyOfB!! ) )
 .map( ResultModel( name=item.name, message=it.body!! ) )
 )
 .toList()
 .onErrorReturn Collections.emptyList() 
 .subscribeOn(Schedulers.io())
 .to LiveDataReactiveStreams.fromPublisher(it) 
 

Because the concatMapSingle() operator knows about each item, its name can be known when it is time to construct the ResultModel. Now, you no longer need to tear things apart so often.

Edit : I found another solution

 override fun methodICall(): LiveData<MutableList<ResultModel>> 
 return mySdk
 .getAllA()
 .concatMapSingle 
 Flowable.fromIterable(it)
 .flatMap a ->
 mySdk.getB(a.propertyOfA!!)
 .flatMap b -> chatbotSdk.getC(b.propertyOfB!!) 
 .map it ->

 ResultModel(name = a.name,
 message = it.body!!)
 .toFlowable() 
 .toList() 
 .onErrorReturn Collections.emptyList() 
 .subscribeOn(Schedulers.io())
 .to LiveDataReactiveStreams.fromPublisher(it) 
 

Original Solution

This is my solution but I think this solution is really messy and it can be improved a lot.

 data class AtoBDTO(var name: String, var b: Flowable<B>) // I wanted to map one object to more than one so I created this. Probably there is a way to do it with rx functions.
 data class BtoCDTO(var name: String, var c: Flowable<C>)



 override fun methodICall(): LiveData<MutableList<ResultModel>> 
 return mySdk
 .getAllA() // Returns Flowable<List<A>>
 .concatMapSingle 
 Flowable.fromIterable(it)
 .map AtoBDTO(it.name!!, 
 mySdk.getB(it.propertyOfA!!).toFlowable()) //getB returns Single B
 .toList()
 
 .concatMapSingle 
 Flowable.fromIterable(it)
 .map 
 BtoCDTO(it.name,
 it.b.concatMapSingle mySdk.getC(it.propertyOfB!!) ) // getC returns Single C
 
 .toList()
 
 .concatMapSingle 
 Flowable.fromIterable(it)
 .map 
 ResultModel(name = it.name,
 message = it.c.blockingFirst().body!!) // I use blocking first because otherwise I can't get rid of flowable
 .toList()
 
 .onErrorReturn Collections.emptyList() 
 .subscribeOn(Schedulers.io())
 .to LiveDataReactiveStreams.fromPublisher(it)