How to attach a database in Room?

@Database(entities = [Staff::class,Product::class,Barcode::class],version = 1,exportSchema = false)
abstract class AppDataBase : RoomDatabase() {
    companion object {
        private var instance: AppDataBase? = null

        fun getInstance(app: Application, path: String): AppDataBase {
            if (instance == null) {
                instance = Room.databaseBuilder(app.applicationContext, AppDataBase::class.java, path)
                    .allowMainThreadQueries()
//                        .addMigrations(Migration_1_2)
                    .setJournalMode(JournalMode.TRUNCATE)
                    .addCallback(object : RoomDatabase.Callback() {
                        override fun onOpen(db: SupportSQLiteDatabase) {
                            super.onOpen(db)
                            attach("Inventory",StartApplication.instance.preferencePath)
                        }
                    })
                    .build()
            }
            return instance!!
        }

        //        private val Migration_1_2 = object : Migration(1, 2) {
//            override fun migrate(database: SupportSQLiteDatabase) {
//            }
//        }

        fun attach(databaseName: String, path: String) {
            val sql = ("ATTACH DATABASE '$path' AS $databaseName")
            instance!!.mDatabase.execSQL(sql)
            Log.e("Appdata", sql)
        }

    }



    @SkipQueryVerification
    @Query("SELECT iy.Bar_Code from inventory.product pt INNER join inventory iy on pt.ITEM_CD = iy.Bar_Code where iy.BAY_NO = 1")
    fun search() : Int