public function checkBagModel($datos, $tabla){
         $stmt = Conexion::conectar() -> prepare("SELECT caja FROM $tabla WHERE bolsa=:bag AND lote=:lotee");
         $stmt -> bindParam(":bag", $datos["cb"], PDO::PARAM_INT);
         $stmt -> bindParam(":lotee", $datos["lT"], PDO::PARAM_INT);
         $stmt->execute();
         $stmt -> fetch();
         if($stmt->rowCount()>0){
            return "existe";
         }else{
            return "no";
         }
         $stmt->close();
    }