I am using Dropbox Store4 (which is something like...

# android

[Zun]

I am using Dropbox Store4 (which is something like a NetworkBoundResource). I am experiencing an issue where my Fetcher is never called because my reader returns a non-null empty list (Store sees this as valid data). How can I adjust my Room DAO to return null if there are no results (so I can successfully trigger Fetch to actually load new data?). See thread for screenshots

[Zun]

DAO

[Zun]

My Store

[Zun]

Only reader is called, Fetcher or Writer is never called

[Zun]

I honestly don't know if this is by design but it returns an empty list but I need a null item

[André Thiele]

What about not using your Dao directly? Can you put some kind of wrapper around it that checks if the list isEmpty and if true, returns null else the list?

[Zun]

I tried out

showDao.loadHomeScreen(now).onEmpty { emit(null ) }

with no success

[André Thiele]

can you confirm that onEmpty is called? i think the flow might still emit the empty list and onEmpty is never called

[Zun]

Welp, I tried out a breakpoint and manually logging but it doesn't seem to get called

[André Thiele]

yes, thats why you need to remove the onEmpty callback and put your dao inside something like ShowLocalDataSource(val showDao: ShowDao) {
loadHomeScreen() : List<...> {
val shows = showDao.loadHomeScreen()
return if (shows.isEmpty()) {
null
else {
shows
}
}
}

[Zun]

It works when using List directly but I need to use Flow/LiveData to constantly observe database changes

[André Thiele]

try creating a new flow inside your localdatasource of Flow<List<>?> and then call flow {} in which you decide to emit(shows) or emit(null)

[André Thiele]

see: Asynchronous Flow | Kotlin (kotlinlang.org)

[André Thiele]

then do

... = flow {
showsDao.loadHomeScreen().collect { shows ->
if (shows.isEmpty) {
emit(null)
} else {
emit(shows)
}
}
}

[Zun]

that works thank you very much! Still wish onEmpty worked because this is quite some lines of code to achieve something simple

[André Thiele]

thats true, great it works. maybe you can shorten this somehow or just include it directly in your store thing but this could get quite messy