首先要使用Room，需要在app/build.gradle文件中添加如下依赖：

apply plugin: 'kotlin-kapt'

dependencies {
    ...
    implementation "androidx.room:room-runtime:2.2.5"
    kapt "androidx.room:room-compiler:2.2.5"
}

实体类的声明：

@Entity
data class UserInfo(var nikeName: String, var gender: Int, var phone: String, var age: Int) {
    @PrimaryKey(autoGenerate = true)
    var id: Long = 0
}

创建Dao接口：

@Dao
interface UserInfoDao {
    @Insert
    fun insertUserInfo(userInfo: UserInfo): Long

    @Update
    fun updateUserInfo(newInfo: UserInfo)

    @Query("select * from UserInfo")
    fun loadAllUsersInfo(): List<UserInfo>

    @Query("select * from UserInfo where age>:age")
    fun loadUserInfoOrderThan(age: Int): List<UserInfo>

    @Delete
    fun deleteUserInfo(user: UserInfo)

    @Query("delete from UserInfo where nikeName=:nikeName")
    fun deleteByNikeName(nikeName: String): Int
}

定义Database：

@Database(version = 1, entities = [UserInfo::class])
abstract class AppDatabase : RoomDatabase() {
    abstract fun userInfoDao(): UserInfoDao

    companion object {
        private var instance: AppDatabase? = null

        @Synchronized
        fun getDatabase(context: Context): AppDatabase {
            instance?.let { return it }
            return Room.databaseBuilder(context.applicationContext, AppDatabase::class.java, "app_database").build()
                .apply {
                    instance = this
                }
        }
    }
}

简单粗暴式数据库升级：

Room.databaseBuilder(context.applicationContext, AppDatabase::class.java, "app_database")
    .fallbackToDestructiveMigration()
    .build()

不销毁原有数据的升级方式：

@Database(version = 2, entities = [UserInfo::class,Book::class])
abstract class AppDatabase : RoomDatabase() {
    abstract fun userInfoDao(): UserInfoDao
    abstract fun bookDao(): BookDao

    companion object {
        private var instance: AppDatabase? = null
        val migration_1_2 = object : Migration(1, 2) {
            override fun migrate(database: SupportSQLiteDatabase) {
                database.execSQL("create table Book(id integer primary key autoincrement not null,name text not null,pages integer not null)")
            }
        }

        @Synchronized
        fun getDatabase(context: Context): AppDatabase {
            instance?.let { return it }
            return Room.databaseBuilder(context.applicationContext, AppDatabase::class.java, "app_database")
                .addMigrations(migration_1_2)
                .build()
                .apply {
                    instance = this
                }
        }
    }
}

插入数据的例子：

    val userInfoDao = AppDatabase.getDatabase(this).userInfoDao()
    val user1 = UserInfo("hyjiao", 0, "18600000000", 25)
    thread {
        user1.id = userInfoDao.insertUserInfo(user1)
    }