Compose + Room：数据库集成与 Flow 观察

2024-06-05 · 24 min · 数据库

Room Database Flow DAO

Room 是 Android 官方的 SQLite 抽象层，提供编译时验证和流畅的 API。结合 Kotlin Flow，可以在 Compose 中实现响应式的数据库观察。

一、DAO with Flow

@Dao
interface ArticleDao {
    
    // 返回 Flow，自动观察变化
    @Query("SELECT * FROM articles ORDER BY published_at DESC")
    fun getAllArticles(): Flow<List<ArticleEntity>>
    
    @Query("SELECT * FROM articles WHERE id = :id")
    fun getArticleById(id: String): Flow<ArticleEntity?>
    
    @Insert(onConflict = OnConflictStrategy.REPLACE)
    suspend fun insert(article: ArticleEntity)
}

二、ViewModel 集成

@HiltViewModel
class ArticleViewModel @Inject constructor(
    private val repository: ArticleRepository
) : ViewModel() {
    
    val articles: StateFlow<List<ArticleEntity>> = repository.allArticles
        .stateIn(
            scope = viewModelScope,
            started = SharingStarted.WhileSubscribed(5000),
            initialValue = emptyList()
        )
}

三、在 Compose 中使用

@Composable
fun ArticleListScreen(viewModel: ArticleViewModel = hiltViewModel()) {
    val articles by viewModel.articles.collectAsState()
    
    LazyColumn {
        items(articles, key = { it.id }) { article ->
            ArticleCard(article)
        }
    }
}

四、数据库迁移

val MIGRATION_1_2 = object : Migration(1, 2) {
    override fun migrate(database: SupportSQLiteDatabase) {
        database.execSQL(
            "ALTER TABLE articles ADD COLUMN category TEXT NOT NULL DEFAULT ''"
        )
    }
}

val database = Room.databaseBuilder(context, AppDatabase::class.java, "app.db")
    .addMigrations(MIGRATION_1_2)
    .build()

五、最佳实践

总结