Adding records to the database using class function - php

Question

I'm trying to add records to the database using function like this:
require_once('../config/Database.php');
class Category {
private $conn;
private $id;
private $name;
private $description;
private $created;
public function __construct($db) {
$this->conn = $db;
}
public function addRecord($n, $desc) {
$this->conn->prepare("INSERT INTO categories VALUES('', '$n', '$desc', CURDATE())")->execute();
$this->name = $n;
$this->description = $desc;
}
and to call it with it:
<?php
if($_SERVER['REQUEST_METHOD'] == 'POST'){
if ( isset( $_POST['addRecord'], $_POST['n'], $_POST['desc']) ) {
$cat = new Category($conn);
$n = filter_input ( INPUT_POST , 'n', FILTER_SANITIZE_STRING );
$desc = filter_input ( INPUT_POST , 'desc', FILTER_SANITIZE_STRING );
$cat->addRecord($n, $desc);
}
}
?>
<div style="border: 5px solid black; width: 40%">
<h3>addRecord($n, $desc):</h3>
<form action="" method="post">
<label>Category name :</label>
<input type="text" name="n" id="n" required="required" placeholder="Please Enter Name"/><br /><br />
<label>Category description :</label>
<input type="text" name="desc" id="desc" required="required" placeholder="Please Enter Description"/><br /><br />
<input type="submit" value="addRecord" name="addRecord"/><br />
</form>
</div>
Database connection is here:
<?php
class Database {
public function getConnection() {
$result = false;
try {
$result = new PDO('mysql:host=localhost;dbname=demo', 'root', '');
} catch(PDOException $e) { }
return $result;
}
}
$db = new Database();
$conn = $db->getConnection();
if (!$conn) {
die("Error connecting to the database");
}
?>
I'm not getting any error but it's not working, just nothing happends when I press the "addRecord" button