Mysqli oop method call - php

Question

I'm really new to implementing OOP using mysqli things, I have this Object(Class) named Database, my real problem is how would I call my select method in my index.php and how can I use it
Database Class.php is below:
Class Database{
private $host = null;
private $user = null;
private $pass = null;
private $db = null;
public $error = "Error Po Sir!";
public $con;
public function connect($host, $user, $pass, $db){
$this->host = $host;
$this->user = $user;
$this->pass = $pass;
$this->db = $db;
$this->con = mysqli_connect($this->host, $this->user, $this->pass);
if(mysqli_connect_errno()){
echo "Connection Failed %s\n!", mysqli_connect_error();
exit();
}
}
public function select($condition){
$query = "select os_user from users WHERE os_user = {$condition}";
$result = mysqli_query($this->con,$query);
return $result;
}
}
this is how did I implement it:
require 'templates/dbclass.php';
$db = new Database();
$db->connect("localhost", "root", "", "os_db");
$username = $_POST['username'];
if($result = $db->select($username)){
echo $username;
if($result->num_rows > 0){
while($row = $result->fetch_object()){
echo $row->os_id;
}
}
}
But it does not show any results. When I var_dump($result) I get bool(false).
I've enabled error reporting, but there is no errors displayed.

Answer 1

There are 3 issues with your select function
is is vulnerable to SQL injection
it does no error checking
it is useless
Here is how it have to be
public function query($sql, $bind)
{
$db = $this->con;
$stm = $db->prepare($sql) or trigger_error($db->error." [$sql]");
$types = str_repeat("s", count($values));
array_unshift($bind, $types);
call_user_func_array(array($stm, 'bind_param'), $bind);
$stm->execute() or trigger_error($db->error." [$sql]");
$stm->store_result();
return $stm->get_result();
}
used like this
$sql = "select os_user from users WHERE os_user = ?";
$res = $db->select($sql, $_POST['username']));
while($row = $result->fetch_object()){
echo $row->os_id;
}