Good morning all. I'm looking to use DataStore in...

# multiplatform

[mattinger]

Good morning all. I'm looking to use DataStore in a KMP project. I've got a data class defined for what i want to represent (it will just be a list of a this data class):

data class StringTableKey(
    val name: String,
    val languageCode: String,
    val countryCode: String
)

interface StringTable {
    fun asMap(): Map<StringTableKey, String>
}

I want to define a DataStore for StringTable. However, it seems that the "Serializer" interface exists only in the android artifact. If that's the case, how am i supposed to define serialization for the iOS side of things?

[Vidmantas Kerbelis]

Yeah. the androidx.datastore.core.Serializer does not exist in common code. If you really want to do it this way - you should expose your store as an expect / actual implementation.

The actual implementation for Android would use the Serializer,
On iOS - use a file solution (`NSDocumentDirectory`and so on),
On JS - use localStorage.

Or, you just use DataStore<Preferences> and save the Map<StringTableKey, String> with a forEach, with no serailization. Though deserializing will be a bit more problematic.

EDIT: You could just serialize the key using JSON and save it as the preference key

[mattinger]

Yeah, i've seen this example in the documentation:

fun createDataStore(): DataStore<Preferences> = createDataStore(
    producePath = {
        val documentDirectory: NSURL? = NSFileManager.defaultManager.URLForDirectory(
            directory = NSDocumentDirectory,
            inDomain = NSUserDomainMask,
            appropriateForURL = null,
            create = false,
            error = null,
        )
        requireNotNull(documentDirectory).path + "/$dataStoreFileName"
    }
)

[mattinger]

And so i'd have to wrap the calls to to this to generate the keys and values from my data structures, and likewise when it reconstitutes.

[mattinger]

That seams reasonable. I can create implementations of my interface backed by a Preferences instance, and provide a transform for the flow you get from the datastore

[mattinger]

Thanks @Vidmantas Kerbelis for the advice:

fun Preferences.asStringTable(): StringTable =
    PreferencesStringTable(this)

fun Flow<Preferences>.toStringTableFlow(): Flow<StringTable> =
    map {
        it.asStringTable()
    }

I think this will work well for me as 99% of the app only wants the immutable version and won't be pushing strings.