首先我們建立的UserData.kt
就是我們資料庫中每一筆資料的欄位

@Entity
data class UserData(
    @PrimaryKey(autoGenerate = true) var uid: Int,
    @ColumnInfo(name = "app_name") var name: String?,
    @ColumnInfo(name = "account") var account: String?,
    @ColumnInfo(name = "password") var password: String?
)

PrimaryKey 代表主鍵
剩下都是其它欄位

以及新增UserDao.kt

import androidx.room.Dao
import androidx.room.Delete
import androidx.room.Insert
import androidx.room.Query

@Dao
interface UserDao {
    @Query("SELECT * FROM users")
    fun getAll(): List<UserData>

    @Query("SELECT * FROM users WHERE uid IN (:userIds)")
    fun loadAllByIds(userIds: IntArray): List<UserData>

    @Query("SELECT * FROM users WHERE app_name LIKE :first AND " +
            "account LIKE :last LIMIT 1")
    fun findByName(first: String, last: String): UserData

    @Insert
    fun insertAll(vararg users: UserData)

    @Delete
    fun delete(user: UserData)
}

此interface主要是操作SQL語法
還有許多資料庫CRUD方法都寫在這

新增Appdatabase.kt

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


@Database(entities = [(UserData::class)], version = 1, exportSchema = false)
abstract class Appdatabase : RoomDatabase() {

    companion object {
        const val DATABASE_NAME = "123.db"
        @Volatile private var instance: Appdatabase? = null
        private val LOCK = Any()

        operator fun invoke(context: Context)= instance ?: synchronized(LOCK){
            instance ?: buildDatabase(context).also { instance = it}
        }

        private fun buildDatabase(context: Context) = Room.databaseBuilder(context,
            Appdatabase::class.java, DATABASE_NAME).build()
    }

    abstract fun getNotesDao(): UserDao
}