---
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]]
