Kotlin 如何通过更改现有数据类型来执行Android房间数据库迁移

我在我的Android应用程序中使用Room数据库，它提供了一个包含Car个元素的表格，如下所示:

@Entity(tableName = "Cars")
data class Car(
    @PrimaryKey(autoGenerate = true) @ColumnInfo(name = "Id") val id: Int? = null,
    @ColumnInfo(name = "Manufacture") var manufacture: String? = null, 
    @ColumnInfo(name = "Model") var model: String? = null,
    @ColumnInfo(name = "Date_created") val dateCreated: String? = null,
    @ColumnInfo(name = "Date_modified") var dateModified: String? = null,
    @ColumnInfo(name = "Color") var color: String? = null,
    @ColumnInfo(name = "Tags") var tags: String? = null
)

现在，我需要对该表执行一些更改，并按如下方式升级它: 现在，我需要在表中应用一些更改:

@Entity(tableName = "Cars")
data class Car(
    @PrimaryKey(autoGenerate = true) @ColumnInfo(name = "Id") var id: Long = 0,
    @ColumnInfo(name = "Manufacture") var manufacture: String = "", 
    @ColumnInfo(name = "Model") var model: String = "",
    @ColumnInfo(name = "Labels") var labels: List<String> = listOf(),
    @ColumnInfo(name = "Color") var color: String? = null,
    @ColumnInfo(name = "Timestamp") var timestamp: Long = 0L,
    @ColumnInfo(name = "Type") var type: Type = Type.Sedan,
    @ColumnInfo(name = "Folder") var folder: Folder = Folder.Used
)

此次升级将对现有表格进行以下更改:

• 第Id栏:val id: Int? = null改为val id: Long = 0.
• 第Manufacture栏:var manufacture: String? = null改为var manufacture: String = "".
• 第Date_created栏:var dateCreated: String? = null栏已删除.
• 列Date_modified重命名为Timestamp，其数据类型也从可为空的String变为不可为空的Long.是否可以在迁移过程中将字符串转换为Long？这些字符串值是转换为字符串timestampe.toString()的时间戳.
• 数据类型var tags: String? = null的列Tags(由逗号分隔的一个字符串中的标签:例如"Gas,Diesel,Oil")改变为列表var labels: List<String> = listOf()的标签.是否可以在迁移时将标签串转换为列表？
• 列Type和Folder是数据类型enum的新列.

我对一些数据类型提出了问题，这些数据类型必须更改为另一种数据类型，因为我找不到任何有关此主题的信息.尽管如此，我还是基于Migrate your Room database和Understanding migrations with Room做了一个小的变通方法，但不确定语法和数据类型转换:

@Database(entities = [Car::class], version = 2, exportSchema = false)
abstract class CarsDatabase : RoomDatabase() {

    abstract val carDao: CarDao

    companion object {

        @Volatile
        private var INSTANCE: CarsDatabase? = null

        private val migration = object : Migration(1, 2) {
            override fun migrate(database: SupportSQLiteDatabase) {
                database.apply {
                    execSQL(
                        "CREATE TABLE cars_tmp (" +
                                "Id INTEGER, " +
                                "Manufacture TEXT, " +
                                "Model TEXT, " +
                                "Timestamp LONG, " + // Not sure about syntax for Long
                                "Labels LIST," + // Not sure about syntax for List<String>
                                "PRIMARY KEY(Id)" +
                                ")"
                    )
                    execSQL("INSERT INTO cars_tmp (" +
                            "Id, Manufacture, Model, Timestamp, Labels, Color) SELECT " +
                            "Id, Manufacture, Model, Date_modified, Tags, Color" + // String of "Date_modified" being converted to Long of "Timestamp" and String of "Tags" being converted to List<String>
                            "FROM Cars"
                    )
                    execSQL("DROP TABLE Car")
                    execSQL("ALTER TABLE cars_tmp RENAME TO Car")
                    execSQL("ALTER TABLE Car ADD COLUMN Type TEXT")
                    execSQL("ALTER TABLE Car ADD COLUMN Folder TEXT")
                }
            }
        }
        
        fun getInstance(context: Context): CarsDatabase = INSTANCE ?: synchronized(this) {
            val instance = Room.databaseBuilder(
                context.applicationContext,
                CarsDatabase::class.java,
                "Cars.db"
            )
                .addMigrations(migration)
                .build()
            INSTANCE = instance
            return instance
        }
    }
}

我不指望有人会做我的工作，但我至少我真的需要一些关于我的问题的答案，以便很好地完成migrations.我对SQL语法非常陌生，因此，我的迁移代码是错误的.

如有任何帮助，敬请惠顾.

编辑: 答案可以在这里找到:How to correctly get the path of Room database on os versions >= 26 sdk?