Issues with Nested Coroutines in Kotlin Flows Not Emitting Values as Expected
I'm wondering if anyone has experience with I'm migrating some code and I'm stuck on something that should probably be simple... I've tried everything I can think of but I'm facing an issue with Kotlin Flows where I'm trying to collect values from a nested flow within a coroutine, but the values are not emitted as expected... I have a parent flow that emits a list of IDs, and for each ID, I want to fetch details from a database using another flow. However, it seems like the inner flow is not being collected properly. Here’s a simplified version of my code: ```kotlin fun fetchData(): Flow<List<Data>> = flow { val ids = getIdsFromApi() // Returns a list of IDs emit(ids) } fun getDataById(id: Int): Flow<Data> = flow { val data = database.getData(id) // Simulate a database query emit(data) } fun processFlows() { viewModelScope.launch { fetchData().collect { ids -> ids.forEach { id -> getDataById(id).collect { data -> // Do something with data } } } } } ``` The issue arises when I run this code; it seems like the inner `collect` block for `getDataById` doesn’t get called at all, and I don’t see any data being processed. I’ve checked the database query, and it returns the expected results when called independently. I’ve tried adding `Log.d` statements to verify each step, but the inner collection doesn’t seem to trigger. I also considered using `flatMapConcat` to simplify the flow, but I’m unsure of the correct usage in this scenario. Any suggestions on how to ensure that the inner flow collects its emitted values properly? I’m using Kotlin 1.5.30 and the latest version of Coroutines and Flow libraries, and this is part of my Android application. For context: I'm using Kotlin on CentOS. How would you solve this? I'm on Ubuntu 22.04 using the latest version of Kotlin. Any pointers in the right direction? Is there a simpler solution I'm overlooking?