datastore

Name: datastore
Author: rcosteira79

39installs13forks

How to install datastore?

rcosteira79/android-skills/datastore

$npx -y skills add rcosteira79/android-skills --skill datastore

Installs into the current project.

Summary

Use when persisting key-value preferences or small typed settings on Android or KMP with Jetpack DataStore — Preferences vs Typed (Proto/JSON) vs Room selection, the IOException and corruption-recovery error traps, serializers with corruption handlers, and the KMP factory with pe

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SKILL.md

1	# Jetpack DataStore for Android and KMP
2
3	Reactive coroutine-based key-value / typed storage; the same `androidx.datastore:datastore-preferences-core` runs on Android, iOS, and JVM — only the file-path producer is platform-specific. (Web support is 1.3.0-alpha only, and it's `sessionStorage`/OPFS-backed there, not file-path-based.) This reference covers the storage-choice call plus the two error/path traps, not the basics of Preferences keys, `edit { }`, or `Serializer<T>`. Adapted from [Meet-Miyani/compose-skill](https://github.com/Meet-Miyani/compose-skill); MIT. Related: `android-skills:android-data-layer`, `android-skills:kmp-boundaries`, `android-skills:kotlin-flows`.
4
5	## Preferences vs Typed vs Room
6
7	\| Need \| Storage \|
8	\|---\|---\|
9	\| Key-value flags (theme, locale, onboarding done) \| Preferences DataStore \|
10	\| One typed object, many related fields, schema evolution \| Typed DataStore + `Serializer<T>` \|
11	\| Relational data, indexes, `WHERE` / `JOIN`, >100 entries, paging \| Room \|
12	\| Payloads above ~50KB per write \| Room / filesystem — DataStore rewrites the whole file on every `edit` \|
13
14	Rule of thumb: if a `WHERE` clause would be useful, use Room.
15
16	## The two traps
17
18	`.catch` must match `IOException` specifically — never a broad `catch`. A bare `catch { emit(emptyPreferences()) }` swallows `CancellationException` (breaking structured concurrency) and hides serializer/corruption errors behind a silent empty state.
19
20	```kotlin
21	val settings: Flow<UserSettings> = dataStore.data
22	.catch { e -> if (e is IOException) emit(emptyPreferences()) else throw e }
23	.map { p -> UserSettings(p[Keys.DARK_MODE] ?: false, p[Keys.LOCALE] ?: "en") }
24	```
25
26	Typed-DataStore corruption recovery triggers on `CorruptionException`, NOT `IOException`. The serializer's `readFrom` must wrap parse failures in `CorruptionException`, and the store needs a `ReplaceFileCorruptionHandler` — without it, one corrupt file makes every read fail permanently.
27
28	```kotlin
29	object AppSettingsSerializer : Serializer<AppSettings> {
30	override val defaultValue = AppSettings()
31	override suspend fun readFrom(input: InputStream): AppSettings =
32	try { Json.decodeFromString(input.readBytes().decodeToString()) }
33	catch (e: SerializationException) { throw CorruptionException("Cannot read AppSettings", e) }
34	override suspend fun writeTo(t: AppSettings, output: OutputStream) =
35	output.write(Json.encodeToString(t).encodeToByteArray())
36	}
37	val store = DataStoreFactory.create(
38	serializer = AppSettingsSerializer,
39	corruptionHandler = ReplaceFileCorruptionHandler { AppSettings() },
40	produceFile = { File(context.filesDir, "app_settings.json") },
41	)
42	```
43
44	## KMP factory — per-platform path (not the temp dir)
45
46	```kotlin
47	// commonMain
48	fun createPreferencesDataStore(producePath: () -> String): DataStore<Preferences> =
49	PreferenceDataStoreFactory.createWithPath(produceFile = { producePath().toPath() })
50	// android: context.filesDir.resolve(PREFS_FILE).absolutePath
51	// ios: NSDocumentDirectory via NSFileManager
52	// jvm: File(System.getProperty("user.home"), ".myapp") — NOT java.io.tmpdir (the OS may wipe it on reboot)
53	```
54
55	(In a composable, never `runBlocking` on DataStore — it parks the main thread on disk I/O, risking an ANR, and re-runs every recomposition. Expose a `StateFlow` and collect with `collectAsStateWithLifecycle`.)

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Type

datastore

39installs13forks

View on GitHub

How to install datastore?

rcosteira79/android-skills/datastore

$npx -y skills add rcosteira79/android-skills --skill datastore

Installs into the current project.

Summary

Files · 1

View on GitHub

SKILL.md

1	# Jetpack DataStore for Android and KMP
2
3	Reactive coroutine-based key-value / typed storage; the same `androidx.datastore:datastore-preferences-core` runs on Android, iOS, and JVM — only the file-path producer is platform-specific. (Web support is 1.3.0-alpha only, and it's `sessionStorage`/OPFS-backed there, not file-path-based.) This reference covers the storage-choice call plus the two error/path traps, not the basics of Preferences keys, `edit { }`, or `Serializer<T>`. Adapted from [Meet-Miyani/compose-skill](https://github.com/Meet-Miyani/compose-skill); MIT. Related: `android-skills:android-data-layer`, `android-skills:kmp-boundaries`, `android-skills:kotlin-flows`.
4
5	## Preferences vs Typed vs Room
6
7	\| Need \| Storage \|
8	\|---\|---\|
9	\| Key-value flags (theme, locale, onboarding done) \| Preferences DataStore \|
10	\| One typed object, many related fields, schema evolution \| Typed DataStore + `Serializer<T>` \|
11	\| Relational data, indexes, `WHERE` / `JOIN`, >100 entries, paging \| Room \|
12	\| Payloads above ~50KB per write \| Room / filesystem — DataStore rewrites the whole file on every `edit` \|
13
14	Rule of thumb: if a `WHERE` clause would be useful, use Room.
15
16	## The two traps
17
18	`.catch` must match `IOException` specifically — never a broad `catch`. A bare `catch { emit(emptyPreferences()) }` swallows `CancellationException` (breaking structured concurrency) and hides serializer/corruption errors behind a silent empty state.
19
20	```kotlin
21	val settings: Flow<UserSettings> = dataStore.data
22	.catch { e -> if (e is IOException) emit(emptyPreferences()) else throw e }
23	.map { p -> UserSettings(p[Keys.DARK_MODE] ?: false, p[Keys.LOCALE] ?: "en") }
24	```
25
26	Typed-DataStore corruption recovery triggers on `CorruptionException`, NOT `IOException`. The serializer's `readFrom` must wrap parse failures in `CorruptionException`, and the store needs a `ReplaceFileCorruptionHandler` — without it, one corrupt file makes every read fail permanently.
27
28	```kotlin
29	object AppSettingsSerializer : Serializer<AppSettings> {
30	override val defaultValue = AppSettings()
31	override suspend fun readFrom(input: InputStream): AppSettings =
32	try { Json.decodeFromString(input.readBytes().decodeToString()) }
33	catch (e: SerializationException) { throw CorruptionException("Cannot read AppSettings", e) }
34	override suspend fun writeTo(t: AppSettings, output: OutputStream) =
35	output.write(Json.encodeToString(t).encodeToByteArray())
36	}
37	val store = DataStoreFactory.create(
38	serializer = AppSettingsSerializer,
39	corruptionHandler = ReplaceFileCorruptionHandler { AppSettings() },
40	produceFile = { File(context.filesDir, "app_settings.json") },
41	)
42	```
43
44	## KMP factory — per-platform path (not the temp dir)
45
46	```kotlin
47	// commonMain
48	fun createPreferencesDataStore(producePath: () -> String): DataStore<Preferences> =
49	PreferenceDataStoreFactory.createWithPath(produceFile = { producePath().toPath() })
50	// android: context.filesDir.resolve(PREFS_FILE).absolutePath
51	// ios: NSDocumentDirectory via NSFileManager
52	// jvm: File(System.getProperty("user.home"), ".myapp") — NOT java.io.tmpdir (the OS may wipe it on reboot)
53	```
54
55	(In a composable, never `runBlocking` on DataStore — it parks the main thread on disk I/O, risking an ANR, and re-runs every recomposition. Expose a `StateFlow` and collect with `collectAsStateWithLifecycle`.)

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6 picks

Type