จะทำการป้องจากการอินเจ็คชั่นใน oop php แบบนี้ยังไงอะครับ

<?php

ob_start();
session_start();


include_once 'Database/db.php';
include_once '../connect.php';

$db->findByAttributes('admin',array(
	'admin_username =' => $_POST[admin_username],
	'admin_password =' => $_POST[admin_password]
	));

	$rs = $db->executeRow();


	if($rs)
	{
		$_SESSION['admin_username'] = $rs['admin_username'];
		header('location: index.php?url=home.php');		
	}else{
		echo "username invalid";
		var_dump($db);
	}

?>

function findByAttributes($table,$attributes)
	{
		$this->sql = "SELECT * FROM $table WHERE  ";
		$count = 0;

		foreach ($attributes as $k => $v) {

			if($count==0)
			{
				$this->sql .="$k'$v'";
			}else{
				$this->sql .=" AND $k '$v'";
			}
			$count++;
		}
		return $this;
	}