android-data-layer

Name: android-data-layer
Author: rcosteira79

49installs13forks

How to install android-data-layer?

rcosteira79/android-skills/android-data-layer

$npx -y skills add rcosteira79/android-skills --skill android-data-layer

Installs into the current project.

Summary

Use when implementing the data layer in Android or KMP — the Repository pattern's layered error-propagation model (repository as the error boundary, sealed DataError, Result placement with and without a domain layer) and Room in commonMain (@ConstructedBy, BundledSQLiteDriver, pe

Files · 1

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SKILL.md

1	# Android Data Layer
2
3	The data layer coordinates data from multiple sources; its public API is repository interfaces, and its internals (DAOs, API services, DTOs) never leak upward. This skill is the canonical home for the error-propagation model, plus the KMP-Room setup. Related: `android-skills:android-retrofit` (Retrofit service/OkHttp/Hilt wiring), `android-skills:android-dev` (overall app architecture).
4
5	## Error propagation — the layered model
6
7	The goal: data-layer errors (`IOException` / `HttpException` / `SQLiteException`) must never reach the ViewModel. Map them to a domain error type at the repository boundary. If the project already has an error convention, match it; otherwise a sealed `DataError` hierarchy is a reasonable default:
8
9	```kotlin
10	sealed class DataError(message: String, cause: Throwable? = null) : Exception(message, cause) {
11	class Network(cause: Throwable) : DataError("Network error", cause)
12	class Server(val code: Int, message: String?) : DataError("Server error $code: $message")
13	class Local(cause: Throwable) : DataError("Local storage error", cause)
14	}
15
16	// repository = error boundary: catch platform exceptions, return Result<T> (no domain layer) or throw DataError (with one)
17	suspend fun refreshNews(): Result<Unit> = withContext(io) {
18	try { newsDao.insertAll(newsApi.fetchLatest().map(NewsDto::toEntity)); Result.success(Unit) }
19	catch (e: IOException) { Result.failure(DataError.Network(e)) }
20	catch (e: HttpException) { Result.failure(DataError.Server(e.code(), e.message())) }
21	}
22	```
23
24	The boundary moves outward by one layer when a domain layer exists:
25
26	1. Data sources throw platform/library exceptions (`IOException`, `HttpException`, `SQLiteException`).
27	2. Repository is the error boundary — catch those and remap to `DataError`; never let raw platform types leak. Without a domain layer (simple MVVM): the repository returns `Result<T>` directly and the ViewModel handles it without knowing about platform exceptions.
28	3. Use cases (when present) are the `Result` boundary — the repository instead throws `DataError`, and the use case catches it and returns `Result<T>` with a domain-specific error model. Use cases never catch platform exception types.
29	4. ViewModels handle `Result<T>` and map it to UI state (explicit loading / success / error).
30
31	(Default to the `Entity` suffix — `ArticleEntity` — for Room types; match an existing convention such as a `Cached` prefix if the project already uses one.)
32
33	## Room in KMP (`commonMain`)
34
35	Room has been KMP-stable since 2.7.0. The shared setup differs from the Android-only setup in three places:
36
37	1. `@ConstructedBy(...)` on the `@Database`, paired with an `expect object` Room generates per-platform `actual`s for.
38	2. `BundledSQLiteDriver` (from `androidx.sqlite:sqlite-bundled`) — pins the same SQLite version across Android/iOS/JVM/web (Android's system SQLite drifts between API levels and devices).
39	3. `setQueryCoroutineContext(Dispatchers.IO)` — Android Room defaults this; KMP doesn't.
40
41	```kotlin
42	// commonMain
43	@Database(entities = [ArticleEntity::class], version = 1, exportSchema = true)
44	@ConstructedBy(AppDatabaseConstructor::class)
45	abstract class AppDatabase : RoomDatabase() { abstract fun articleDao(): ArticleDao }
46
47	@Suppress("KotlinNoActualForExpect")
48	expect object AppDatabaseConstructor : RoomDatabaseConstructor<AppDatabase>
49
50	fun getRoomDatabase(builder: RoomDatabase.Builder<AppDatabase>): AppDatabase =
51	builder.setDriver(BundledSQLiteDriver()).setQueryCoroutineContext(Dispatchers.IO).build()
52	```
53
54	Each platform provides its own builder — Android `Room.databaseBuilder(context, AppDatabase::class.java, "app.db")`; iOS/JVM `Room.databaseBuilder<AppDatabase>(databasePath = …)`. KSP must be wired per target (`ksp(libs.androidx.room.compiler)` is Android-only):
55
56	```kotlin
57	dependencies {
58	add("kspAndroid", libs.androidx.room.compiler)
59	add("kspIosArm64", libs.androidx.room.compiler)
60	add("kspIosSimulatorArm64", libs.androidx.room.compiler)
61	// … one per target
62	}
63	room { schemaDirectory("$projectDir/schemas") } // export the schema for migration-history tracking
64	```
65
66	For pure-Android projects, skip `@ConstructedBy` and call `Room.databaseBuilder(context, AppDatabase::class.java, "app.db")` directly — Room behaves identically; the KMP setup is opt-in when the data layer must live in `commonMain`.

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android-data-layer

49installs13forks

View on GitHub

How to install android-data-layer?

rcosteira79/android-skills/android-data-layer

$npx -y skills add rcosteira79/android-skills --skill android-data-layer

Installs into the current project.

Summary

Files · 1

View on GitHub

SKILL.md

1	# Android Data Layer
2
3	The data layer coordinates data from multiple sources; its public API is repository interfaces, and its internals (DAOs, API services, DTOs) never leak upward. This skill is the canonical home for the error-propagation model, plus the KMP-Room setup. Related: `android-skills:android-retrofit` (Retrofit service/OkHttp/Hilt wiring), `android-skills:android-dev` (overall app architecture).
4
5	## Error propagation — the layered model
6
7	The goal: data-layer errors (`IOException` / `HttpException` / `SQLiteException`) must never reach the ViewModel. Map them to a domain error type at the repository boundary. If the project already has an error convention, match it; otherwise a sealed `DataError` hierarchy is a reasonable default:
8
9	```kotlin
10	sealed class DataError(message: String, cause: Throwable? = null) : Exception(message, cause) {
11	class Network(cause: Throwable) : DataError("Network error", cause)
12	class Server(val code: Int, message: String?) : DataError("Server error $code: $message")
13	class Local(cause: Throwable) : DataError("Local storage error", cause)
14	}
15
16	// repository = error boundary: catch platform exceptions, return Result<T> (no domain layer) or throw DataError (with one)
17	suspend fun refreshNews(): Result<Unit> = withContext(io) {
18	try { newsDao.insertAll(newsApi.fetchLatest().map(NewsDto::toEntity)); Result.success(Unit) }
19	catch (e: IOException) { Result.failure(DataError.Network(e)) }
20	catch (e: HttpException) { Result.failure(DataError.Server(e.code(), e.message())) }
21	}
22	```
23
24	The boundary moves outward by one layer when a domain layer exists:
25
26	1. Data sources throw platform/library exceptions (`IOException`, `HttpException`, `SQLiteException`).
27	2. Repository is the error boundary — catch those and remap to `DataError`; never let raw platform types leak. Without a domain layer (simple MVVM): the repository returns `Result<T>` directly and the ViewModel handles it without knowing about platform exceptions.
28	3. Use cases (when present) are the `Result` boundary — the repository instead throws `DataError`, and the use case catches it and returns `Result<T>` with a domain-specific error model. Use cases never catch platform exception types.
29	4. ViewModels handle `Result<T>` and map it to UI state (explicit loading / success / error).
30
31	(Default to the `Entity` suffix — `ArticleEntity` — for Room types; match an existing convention such as a `Cached` prefix if the project already uses one.)
32
33	## Room in KMP (`commonMain`)
34
35	Room has been KMP-stable since 2.7.0. The shared setup differs from the Android-only setup in three places:
36
37	1. `@ConstructedBy(...)` on the `@Database`, paired with an `expect object` Room generates per-platform `actual`s for.
38	2. `BundledSQLiteDriver` (from `androidx.sqlite:sqlite-bundled`) — pins the same SQLite version across Android/iOS/JVM/web (Android's system SQLite drifts between API levels and devices).
39	3. `setQueryCoroutineContext(Dispatchers.IO)` — Android Room defaults this; KMP doesn't.
40
41	```kotlin
42	// commonMain
43	@Database(entities = [ArticleEntity::class], version = 1, exportSchema = true)
44	@ConstructedBy(AppDatabaseConstructor::class)
45	abstract class AppDatabase : RoomDatabase() { abstract fun articleDao(): ArticleDao }
46
47	@Suppress("KotlinNoActualForExpect")
48	expect object AppDatabaseConstructor : RoomDatabaseConstructor<AppDatabase>
49
50	fun getRoomDatabase(builder: RoomDatabase.Builder<AppDatabase>): AppDatabase =
51	builder.setDriver(BundledSQLiteDriver()).setQueryCoroutineContext(Dispatchers.IO).build()
52	```
53
54	Each platform provides its own builder — Android `Room.databaseBuilder(context, AppDatabase::class.java, "app.db")`; iOS/JVM `Room.databaseBuilder<AppDatabase>(databasePath = …)`. KSP must be wired per target (`ksp(libs.androidx.room.compiler)` is Android-only):
55
56	```kotlin
57	dependencies {
58	add("kspAndroid", libs.androidx.room.compiler)
59	add("kspIosArm64", libs.androidx.room.compiler)
60	add("kspIosSimulatorArm64", libs.androidx.room.compiler)
61	// … one per target
62	}
63	room { schemaDirectory("$projectDir/schemas") } // export the schema for migration-history tracking
64	```
65
66	For pure-Android projects, skip `@ConstructedBy` and call `Room.databaseBuilder(context, AppDatabase::class.java, "app.db")` directly — Room behaves identically; the KMP setup is opt-in when the data layer must live in `commonMain`.

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