# Andriod Studio RoomDB

1. 新增相依套件（build.gradle）
在 app/build.gradle 中加入：

implementation "androidx.room:room-runtime:2.6.1"
annotationProcessor "androidx.room:room-compiler:2.6.1"

// 如果使用 Kotlin kapt（推薦）
kapt "androidx.room:room-compiler:2.6.1"

// 可選：協程支援
implementation "androidx.room:room-ktx:2.6.1"

2.定義 Entity（資料表）**你要存的資料**

import androidx.room.Entity
import androidx.room.PrimaryKey

@Entity(tableName = "user_table")
data class User(
    @PrimaryKey(autoGenerate = true) val id: Int = 0,
    val name: String,
    val age: Int
)

3.定義 DAO（資料存取物件）**怎麼存、怎麼讀**

import androidx.room.*

@Dao
interface UserDao {
    @Insert
    suspend fun insert(user: User)

    @Query("SELECT * FROM user_table")
    suspend fun getAll(): List<User>

    @Delete
    suspend fun delete(user: User)
}

4. 建立 Database 類別 **唯一連線用的**

import android.content.Context
import androidx.room.Database
import androidx.room.Room
import androidx.room.RoomDatabase

@Database(entities = [User::class], version = 1)
abstract class AppDatabase : RoomDatabase() {
    abstract fun userDao(): UserDao

    companion object {
        @Volatile private var INSTANCE: AppDatabase? = null

        fun getDatabase(context: Context): AppDatabase {
            return INSTANCE ?: synchronized(this) {
                Room.databaseBuilder(
                    context.applicationContext,
                    AppDatabase::class.java,
                    "app_database"
                ).build().also { INSTANCE = it }
            }
        }
    }
}

5.在 ViewModel 或 Repository 中使用

val db = AppDatabase.getDatabase(context)
val userDao = db.userDao()

CoroutineScope(Dispatchers.IO).launch {
    userDao.insert(User(name = "小明", age = 20))
    val allUsers = userDao.getAll()
}

**build.gradle 記得要加入：**

implementation "androidx.room:room-runtime:2.6.1"
kapt "androidx.room:room-compiler:2.6.1"
implementation "androidx.room:room-ktx:2.6.1"

記得加這行（在 build.gradle.kts 或 build.gradle 中）：

apply plugin: 'kotlin-kapt'