Help me

<?php
	class Shortener {
		protected $db;

		public function __construct() {
			$this->db = new mysqli('HOST', 'USER', 'WW', 'DB'); <-- even weg gehaald
		}

		public function generateCode($num) {
			return base_convert($num, 10, 36);
		}

		public function makeCode($url) {
			$url = trim($url);

			if(!filter_var($url, FILTER_VALIDATE_URL)) {
				return '';
			}

			$url = $this->db->escape_string($url);
			return $url;

			// Kijken of de link al bestaat
			$exists = $this->db->query("SELECT code FROM links WHERE url = '{$url}'");

			if($exists->num_rows) {
				return $exists->fetch_object()->code;
			} else {
				$this->db->query("INSERT INTO links (url, created) VALUES ('{$url}', NOW())");
				$code = $this->generateCode($this->db->insert_id);
				$this->db->query("UPDATE links SET code = '{$code}' WHERE url = '{$url}'");

				return $code;
			}
		}

		public function getUrl($code) {
			$code = $this->db->escape_string($code);
			$code = $this->db->query("SELECT url FROM links WHERE = '$code'");

			if($code->num_rows) {
				return $code->fetch_object()->url;
			}

			return '';
		}
	}
?>