我正在使用房间数据库创建本地存储，我正在尝试迁移数据库，但在多次调用迁移函数时遇到问题。
我在这里附上我的代码。

class DbInstance {
companion object {
    private var db: AppDatabase? = null
    fun getDbInstance(context: Context): AppDatabase {
        if (db == null)
            db = Room.databaseBuilder(
                context,
                AppDatabase::class.java, "mydb"
            )
                .addMigrations(MIGRATION_1_2, MIGRATION_2_3)
                .build()
        return db!!
    }

    private val MIGRATION_1_2 = object : Migration(1, 2) {
        override fun migrate(database: SupportSQLiteDatabase) {

        }
    }
    private val MIGRATION_2_3 = object : Migration(2, 3) {
        override fun migrate(database: SupportSQLiteDatabase) {
            println("------> called for MIGRATION_2_3")
            database.execSQL(
                "Alter table PaymentDB add column ui_name text"
            )
        }
    }
  }
}


@Database(entities = arrayOf(PaymentDB::class), version = 3)
@TypeConverters(DbTypeConverter::class)
abstract class AppDatabase : RoomDatabase() {
    abstract fun paymentDao(): PaymentDao
}

其中println("------> called for MIGRATION_2_3")打印了多次（两次）。