Hello I'm using the new version of Room and I'd like to start using `Flow` so what I want to do is c...

# coroutines

[Pablo]

Hello I'm using the new version of Room and I'd like to start using Flow so what I want to do is change the List<Animals> to a Flow<List<Animals>> but then, I'm losing the mappers on my use-case and on my presentation ? Is there any way to keep mapping the values from the data layer? I mean, my dao now returns a Flow<List<Animals>> do I have to change also the repository return to be a Flow<List<Animals>> ? I had a return List<AnimalsMappedToDomain> , but now how can I do that mapper? What would be the flow from repository to presentation using the mappers?

[bezrukov]

just use flow.map:

fun animalFlow(): Flow<List<AnimalsMappedToDomain> = dao.animals.map { animals ->
   animals.map { animal ->
      animal.mapToDomain()
   }
}

[Pablo]

Yes, I found this way to do it, the problem comes when I'm on the use-case didn't mention that, that the return is an Either<Exception,List<AnimalsMappedtoDomain>>

[Pablo]

Got me? I mean before I was using this Either and then on my ViewModel I was using the fold to get the Left and Right now that I'm changing to Flow don't know how to tract this

[bezrukov]

what kind of error do you expect here? typically queries that return List doesn't produce errors (except the cases when your DB is corrupted for example, but handling such exceptions in each query is a bad practice IMO).

[Pablo]

Well I've created like different types of layout like for emptyList NetworkConnection, so from Repository I throw these exceptions and then on domain I convert these Either the exception or the list to an Either so on my ViewModel I can show the list or other layout

[bezrukov]

But if you want to return Flow<Either<Exception, List<Animal>>, you can write top-level fun that converts Flow<T> to Flow<Either<Exception, T>>

fun Flow<T>.handleErrors() = flow {
   try {
       collect {
          emit( // either with element)
       }
   } catch (e: Exception) { 
       emit(// either with error)
   }
}

Another option is to expose Flow<List<Animal...>> and in VM use .catch operator

[Pablo]

So on my domain can I still use this Either<Exception, List<T>>? Or do I have to change it

[Pablo]

?