[G1-Sync] Manual knowledge update

2026-05-09 21:08:02 +09:00
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+---
+id: android-room-patterns
+title: Android Room — 안전한 SQLite ORM
+category: Coding
+status: draft
+source_trust_level: B
+verification_status: conceptual
+created_at: 2026-05-09
+updated_at: 2026-05-09
+tags: [android, room, sqlite, persistence, vibe-coding]
+tech_stack: { language: "Kotlin / Room", applicable_to: ["Android"] }
+applied_in: []
+aliases: [Room, DAO, Entity, Migration, Flow]
+---
+
+# Android Room
+
+> 컴파일 타임 SQL 검증 + Flow 기반 reactive 쿼리. **Entity / DAO / Database** 3종. Migration 제대로 안 하면 사용자 데이터 손실 사고.
+
+## 📖 핵심 개념
+- Entity: @Entity 클래스 = 테이블.
+- DAO: @Dao 인터페이스 = 쿼리 모음.
+- Database: @Database — abstract class.
+- Coroutines + Flow 자동 통합.
+
+## 💻 코드 패턴
+
+### Entity + DAO + DB
+```kotlin
+@Entity(tableName = "users", indices = [Index(value = ["email"], unique = true)])
+data class UserEntity(
+    @PrimaryKey val id: String,
+    val email: String,
+    val name: String,
+    val createdAt: Long,
+)
+
+@Dao
+interface UserDao {
+    @Query("SELECT * FROM users WHERE id = :id")
+    suspend fun findById(id: String): UserEntity?
+
+    @Query("SELECT * FROM users ORDER BY created_at DESC LIMIT :limit")
+    fun observeRecent(limit: Int): Flow<List<UserEntity>>
+
+    @Insert(onConflict = OnConflictStrategy.REPLACE)
+    suspend fun upsert(user: UserEntity)
+
+    @Update
+    suspend fun update(user: UserEntity)
+
+    @Query("DELETE FROM users WHERE id = :id")
+    suspend fun delete(id: String)
+}
+
+@Database(entities = [UserEntity::class], version = 2, exportSchema = true)
+abstract class AppDb : RoomDatabase() {
+    abstract fun userDao(): UserDao
+}
+```
+
+### Migration
+```kotlin
+val MIGRATION_1_2 = object : Migration(1, 2) {
+    override fun migrate(db: SupportSQLiteDatabase) {
+        db.execSQL("ALTER TABLE users ADD COLUMN avatar_url TEXT")
+    }
+}
+
+Room.databaseBuilder(ctx, AppDb::class.java, "app.db")
+    .addMigrations(MIGRATION_1_2)
+    .build()
+```
+
+### Repository + Flow
+```kotlin
+class UserRepository(private val dao: UserDao, private val api: UserApi) {
+    fun observeUser(id: String): Flow<User> = dao.observeUser(id).map { it.toDomain() }
+
+    suspend fun refresh(id: String) {
+        val u = api.fetch(id)
+        dao.upsert(u.toEntity())
+    }
+}
+```
+
+### Type converters
+```kotlin
+class Converters {
+    @TypeConverter fun fromInstant(t: Instant?): Long? = t?.toEpochMilli()
+    @TypeConverter fun toInstant(ms: Long?): Instant? = ms?.let { Instant.ofEpochMilli(it) }
+}
+
+@Database(entities = [...], version = 1)
+@TypeConverters(Converters::class)
+abstract class AppDb : RoomDatabase() { ... }
+```
+
+## 🤔 의사결정 기준
+| 데이터 | 도구 |
+|---|---|
+| 구조화 데이터, 쿼리 필요 | Room |
+| Key-value 설정 | DataStore |
+| 큰 파일 | File API |
+| 비밀 (token) | EncryptedSharedPreferences / Keystore |
+| Sync (서버) | Room + WorkManager |
+| 검색 | FTS5 (Room 지원) |
+
+## ❌ 안티패턴
+- **main thread 에서 DB 호출**: ANR. suspend / Flow 만.
+- **migration 안 쓰고 fallbackToDestructiveMigration**: 사용자 데이터 손실.
+- **DB schema 변경 후 version 안 올림**: crash on launch.
+- **거대 트랜잭션 + 외부 API 호출 안에**: lock 길어짐.
+- **Entity 노출 (UI 까지)**: domain 과 결합. mapper 권장.
+- **인덱스 누락**: 큰 테이블 query 느림.
+- **exportSchema = false**: schema 변경 검증 못 함. CI 에서 schema diff.
+
+## 🤖 LLM 활용 힌트
+- 신규 = Room. 단순 KV = DataStore.
+- migration 매 version 마다.
+- Flow + collectAsStateWithLifecycle 패턴.
+
+## 🔗 관련 문서
+- [[Android_DataStore_Patterns]]
+- [[Android_Flow_StateFlow_SharedFlow]]