2nd/10_Wiki/Topic_Programming/Coding/Android_Room_Patterns.md

id, title, category, status, source_trust_level, verification_status, created_at, updated_at, tags, tech_stack, applied_in, aliases

id	title	category	status	source_trust_level	verification_status	created_at	updated_at	tags	tech_stack	applied_in	aliases
android-room-patterns	Android Room — 안전한 SQLite ORM	Coding	draft	B	conceptual	2026-05-09	2026-05-09	android room sqlite persistence vibe-coding	language applicable_to Kotlin / Room Android		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

@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

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

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

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