Can't write/read from database - php

Question

I am trying to make a 1 on 1 chat website by learning as I progress, but I've come to a hault.
I can't write to the database.
I have four php files linked below.
Index
Init:
session_start();
define('LOGGED_IN', true);
require 'classes/Core.php';
require 'classes/Chat.php';
?>
Chat
Core:
class Core {
protected $db, $result;
private $rows;
public function __construct() {
$this->db = new mysqli("localhost","root","");
}
public function query($sql) {
$this->result = $this->db->query($sql);
}
public function rows() {
for($x = 1; $x <= $this->db->affected_rows; $x++) {
$this->rows[] = $this->result->fetch_assoc();
}
return $this->rows;
}
}
?>
I have a MySql database set with WAMP.
P.S. Yes, I have opened the "< ? php"
but it doesn't get displayed here.

Answer 1

From what I have seen you do not select a default database. You must either give a default database in
$this->db = new mysqli("localhost","root","", "mydatabase");
or select one later with
$this->db->select_db("mydatabase");
You also don't check the return values of the mysql calls. For example, add
public function query($sql) {
$this->result = $this->db->query($sql);
if ($this->result === false) {
echo $this->db->error;
}
}
after your mysql statements, in order to see whether the statements succeed or fail.
For debugging purposes you can display the sql and corresponding result
public function query($sql) {
var_dump($sql);
$this->result = $this->db->query($sql);
var_dump($this->result);
echo $this->db->error;
}