DataLayer - DataStore

Jetpack DataStore is a data storage solution that allows you to store key-value pairs or typed objects with protocol 
buffers. DataStore uses Kotlin coroutines and Flow to store data asynchronously, consistently, and transactionally.

Introduction

-> Jetpack Library
-> Based on Coroutines & flows
-> Safe and Consistent

Types of Implementation

-> Preferences DataStore
-> Proto DataStore

Preferences DataStore

-> Stores and Accesses data using (key-value) pairs
-> Work asynchronously
-> Runs on background thread (Dispatchers.IO)
-> Easy & quick Migration
-> No type Safety

Proto DataStore

-> Typed Object (e.g. enum, lists, custom objects)
-> Stores data as instances of a custom data type
-> Work asynchronously
-> Runs on background thread (Dispatchers.IO)
-> Easy & quick Migration
-> Requires you to define a schema using protocol buffers for type safety.

Using DataStore correctly

-> Never create more than one instance of DataStore for a given file in the same process.
-> The generic type of the DataStore must be immutable.
-> Never mix usages of SingleProcessDataStore and MultiProcessDataStore

Preference Implementation

Step - 1

Create an instance as follow:

private val Context.dataStore: DataStore<Preferences> by preferencesDataStore(name = "preferencesDataStore")

Step - 2

Generate a key:

private val dataKey = stringPreferencesKey("data")

Step - 3

Save data as:

fun save(data: String) {
	CoroutineScope(Dispatchers.Main).launch {
		context.dataStore.edit {
			it[dataKey] = data
		}
	}
}

Step - 4

Retrieve data as:

private fun getDataPrefs(): Flow<String> = context.dataStore.data
    .catch {
        Log.e(TAG, "getDataPrefs: ", it)
        showToast(context, it)
        if (it is IOException) {
            emit(emptyPreferences())
        } else {
            throw it
        }
    }.map {
        // No type safety.
        return@map it[dataKey] ?: "nill"
    }

We can use flow as liveData for live updates

val dataPrefs = getDataPrefs().asLiveData()

To observe:

dataPrefs.observe(this) {
	Log.d("TAG", "Result: $it")
}

Proto Implementation

Step - 1

Add a plugin for protocol-buffer in Android Studio 'Protocol Buffers'

Step - 2

Create a file of 'proto' extension in the following path.

Project > app > src > main > proto (create a new directory) > data.proto (create a new file)

Step - 3

Write a schema with the help of documentation and protobuf with gradle (plugin)

-> Proto3 Documentation

-> ProtoBug with Gradle

Step - 1

Create an instance as follow:

private val Context.dataStore: DataStore<Preferences> by preferencesDataStore(name = "preferencesDataStore")

Step - 2

Generate a key:

private val dataKey = stringPreferencesKey("data")