Can anyone sanity check this `channelFlow`? It see...

# coroutines

[Florian]

Can anyone sanity check this channelFlow? It seems to work as intended, I just want to make sure I'm not doing anything dumb. The point here is to have Loading inside the launch block emit updates while the try block is running concurrently. I think I don't need to call awaitClose because collection from the query never ends.

inline fun <ResultType, RequestType> networkBoundResource(
    crossinline query: () -> Flow<ResultType>,
    crossinline fetch: suspend () -> RequestType,
    crossinline saveFetchResult: suspend (RequestType) -> Unit,
    crossinline onFetchSuccess: () -> Unit = { },
    crossinline onFetchFailed: (Throwable) -> Unit = { },
    crossinline shouldFetch: (ResultType) -> Boolean = { true }
) = channelFlow {
    val data = query().first()

    if (shouldFetch(data)) {
        val loading = launch {
            query().collect { send(Resource.Loading(it)) }
        }

        try {
            saveFetchResult(fetch())
            onFetchSuccess()
            loading.cancel()
            query().collect { send(Resource.Success(it)) }
        } catch (t: Throwable) {
            onFetchFailed(t)
            loading.cancel()
            query().collect { send(Resource.Error(t, it)) }
        }
    } else {
        query().collect { send(Resource.Success(it)) }
    }
}

[KamilH]

I’ve got a question, maybe a little bit off topic, but if you are persisting your network data in the database, wouldn’t it be easier to build your app around Flow<T> emitted by the database as a single source of truth?
Let’s say you have “UseCase/Interactor” layer in your app, then when you want to get data you have two of them:
• ObserveData - delegates a call to the database that returns Flow<Data>
• RefreshData - contains a reference to NetworkSource and DatabaseSource as well as a logic whether some data should be refreshed (according to shouldFetch function). This class can emit whether fetch was needed, there was a fetch error, or success and also if loading is happening right now. Or simply be suspending Resource<Unit>
In this case responsibilities between the components in the app seems a bit more clear

[Florian]

But the database is the single source of truth here, what makes you think otherwise?

[Florian]

Everything we send through the Flow comes from the DB

[Florian]

We just wrap it into Resource so it contains the data and loading state