房间迁移，尝试重新打开已关闭的对象：SQLiteDatabase

Question

我有简单的Singleton数据库和miration_1_2，所以它很简单，可能就是这样的例子。您可以看到数据库类

@Database(entities = [Feed::class, NewsWidget::class, NewsWidgetFeed::class], version = 2)
abstract class Database : RoomDatabase() {

abstract fun feedDao(): FeedDao
abstract fun newsWidgetDao(): NewsWidgetDao
abstract fun newsWidgetFeedDao(): NewsWidgetFeedDao

companion object {

    @Volatile private var INSTANCE: com.example.Database? = null

    fun getInstance(context: Context): com.example.Database =
            INSTANCE ?: synchronized(this) {
                INSTANCE ?: buildDatabase(context).also { INSTANCE = it }
            }

    private val IO_EXECUTOR = Executors.newSingleThreadExecutor()

    /**
     * Utility method to run blocks on a dedicated background thread, used for io/database work.
     */
    fun ioThread(f: () -> Unit) {
        IO_EXECUTOR.execute(f)
    }

    private fun buildDatabase(context: Context) =
            Room.databaseBuilder(context.applicationContext,
                    com.example.Database::class.java, "settings.db")
                    .addMigrations(MIGRATION_1_2)
                    .fallbackToDestructiveMigration()
                    .addCallback(object : RoomDatabase.Callback() {
                        override fun onOpen(db: SupportSQLiteDatabase) {
                            LogManager.LogEA(db.version)
                            super.onOpen(db)

                        }

                        override fun onCreate(db: SupportSQLiteDatabase) {
                            super.onCreate(db)
                            ioThread {
                                getInstance(context).feedDao().insert(*INIT_FEED_TABLE)
                            }
                        }
                    })
                    .build()

    val MIGRATION_1_2: Migration = object: Migration(1, 2) {
        override fun migrate(database: SupportSQLiteDatabase) {
            database.execSQL("ALTER TABLE NewsWidget ADD COLUMN interval_anim INTEGER DEFAULT 6000")
        }
    }

    val INIT_FEED_TABLE = arrayOf(              
            Feed("https://geektimes.ru/rss/interesting/"),
            Feed("http://k.img.com.ua/rss/ru/companies.xml"))
}

}

当我打电话

 Database.getInstance(context)
 Database.getInstance(context)

或

Database.getInstance(this).feedDao().getAllFeed()
.flatMap({ url -> Database.getInstance(this).feedDao().getItem(url)}) 

我看到错误消息 java.lang.IllegalStateException: attempt to re-open an already-closed object: SQLiteDatabase 我知道问题是两次调用onMigrate。我如何添加onUpgrade回调？如何解决？感谢您的支持。