Room vs DataStore: Which Should You Use?

"Where do I save this?" comes up constantly. A theme preference, a list of 5,000 transactions, the last-opened tab, an onboarding flag, cached articles. Using a database for one boolean is overkill. Using key-value storage for thousands of records is a mistake. Here's how to choose.

Quick answer

DataStore

DataStore replaces SharedPreferences. It's asynchronous (Flow and suspend), consistent (transactional updates), and safe to call from the UI thread because I/O happens off the main thread. It's designed for small datasets, and every update rewrites the whole file.

private val Context.settingsStore by preferencesDataStore(name = "settings")   // one instance per file

enum class ThemeMode { SYSTEM, LIGHT, DARK }
data class Settings(val theme: ThemeMode, val onboardingDone: Boolean)

class SettingsRepository(private val context: Context) {
    private object Keys {
        val THEME = stringPreferencesKey("theme")
        val ONBOARDED = booleanPreferencesKey("onboarding_done")
    }

    val settings: Flow<Settings> = context.settingsStore.data
        .catch { e -> if (e is IOException) emit(emptyPreferences()) else throw e }   // corrupted/unreadable file
        .map { p ->
            Settings(
                theme = p[Keys.THEME]?.let { runCatching { ThemeMode.valueOf(it) }.getOrNull() } ?: ThemeMode.SYSTEM,
                onboardingDone = p[Keys.ONBOARDED] ?: false,
            )
        }

    suspend fun setTheme(mode: ThemeMode) = context.settingsStore.edit { it[Keys.THEME] = mode.name }
    suspend fun completeOnboarding() = context.settingsStore.edit { it[Keys.ONBOARDED] = true }
}

Room

Room is a full SQLite database: indexed queries, relations, partial updates, paging, and observation per table. Use it whenever data is a collection, or you need to filter or sort. See the Room tutorial.

Side-by-side

Migrating from SharedPreferences

private val Context.settingsStore by preferencesDataStore(
    name = "settings",
    produceMigrations = { context -> listOf(SharedPreferencesMigration(context, "legacy_prefs")) },
)

Examples

Common mistakes

• Storing large lists as JSON strings in DataStore or SharedPreferences.
• Creating multiple DataStore instances for the same file, which throws an error at runtime.
• Blocking reads with runBlocking { dataStore.data.first() } on the main thread.
• Putting secrets in plain DataStore.

Frequently asked questions

Conclusion

DataStore for small settings and flags, Room for collections you query, files for large binaries, and Keystore-backed encryption for secrets. Most production apps use more than one, each for what it does best.

Next step: combine local and remote data in Offline-First Android App Architecture.