hey, think im writing myself in a corner with our current async architecture simple usecase: we are ...

# coroutines

[abbic]

hey, think im writing myself in a corner with our current async architecture
simple usecase:
we are getting a flow from a database, and want to observe it as livedata.
however, getting this flow requires data from another base, so the function to get this flow looks like

suspend fun getBalanceFlow(): Flow<Double> {
   val session = sessionDao.getCurrentSession() // suspend fun
   return balanceDao.getBalanceFlow(session.userId)
}

in the viewmodel, we cant write

val balance = getBalanceFlow().asLivedata()

because getBalanceFlow must be a suspend function! any way around this?

[Casey Brooks]

Since you’re returning a flow, getBalanceFlow() should not be marked with suspend. You should try to rewrite that function so that the initial getCurrentSession() call happens within the flow, instead of being needed to create the flow.

This can usually be done pretty easily by creating a flow{ } and using emitAll with the upstream flow:

ffun getBalanceFlow(): Flow<Double> {
    return flow {
        val session = sessionDao.getCurrentSession() // suspend fun
        emitAll(balanceDao.getBalanceFlow(session.userId))
    }
}

[abbic]

whoa

[abbic]

thank you!

[Casey Brooks]

The only thing to watch for with this kind of wrapping logic is to respect the execution context of the flow.

https://elizarov.medium.com/execution-context-of-kotlin-flows-b8c151c9309b

[abbic]

oh interesting.. am i understanding correctly that, if as it happens getCurrentSession() contains code wrapped in withContext(<http://Dispatchers.IO|Dispatchers.IO>), that would be a problem?

[abbic]

or maybe not.. since it doesnt emit anything itself

[Casey Brooks]

No, that would be fine, there’s a snippet in the article showing exactly that

[Casey Brooks]

That’s correct, because getCurrentSession() does not emit anything

[Casey Brooks]

Just don’t wrap the entire flow’s block in withContext()

[abbic]

cool, thanks

[abbic]

doesnt seem too prohibitive

[Casey Brooks]

Yeah, it’s not difficult to work around, just something to keep in mind. And the Flow APIs will throw errors if you break this rule too, which is nice