I have a flow with ids, and I wanna to get flow of...

# squarelibraries

[Philip Dukhov]

I have a flow with ids, and I wanna to get flow of database objects. I’m trying to do it like this:

indicesFlow
    .map { indices ->
        database.usersQueries
            .getBy(indices)
            .asFlow()
            .mapToList()
    }
    .flattenConcat()
    .collect { users ->

    }

For some reason map gets called only for the first emitted item, and when I emit new indices to indexesFlow it’s not get called anymore and so collect it not get called too. I expect old database flow to be cancelled and be replaced with a new one.
And if I replace database flow with a basic flow with emit, same code work fine for new indexesFlow emits

indicesFlow
    .map { indices ->
        flow {
            emit("$indices")
        }
    }
    .flattenConcat()
    .collect { strings ->

    }

I’m just starting exploring flows, what am I missing here?

[Nikky]

sqldelight flows never "end" see: https://kotlinlang.slack.com/archives/C5HT9AL7Q/p1622166059055900
so i am not sure how flattenConcat() handles multiple ongoing flows.. or if that is what you want
`you probably want to call

[Nikky]

but i think mapToList() might be stalling your code

[Nikky]

try withContext(IO) { query.execute() } if you want for each id in indexFlow to execute the query only once

[Philip Dukhov]

ok, I was wrong when thought that flattenConcat will cancel previous flow, there’s flatMapLatest for this purpose, and it works as expected. Still not sure why with flattenConcat new items are not getting passed: all flows created inside map should continue passing values in this case.

[myanmarking]

just get rid of the map and concat, and just use flatmaplatest directly