Trouble entering session variables into mysql - php

Question

So I'm trying to input some session variables into the database, and I'm successfuly inserting all rows, except the $_SESSION['organisationId']. Some context: A user lands on a url as the one given in the snippit below, I get the organisationId, then want that user to be assigned that organisationId when they create the account - working as a sort of 'invite-system' of sorts.
// This is the URL I am using: http://thisapp.com/login.php?competitionId=51da7ed4d686a&organisationId=51d81cab92709
<?php
session_start();
ob_start();
ini_set('display_errors',1);
ini_set('display_startup_errors',1);
error_reporting(-1);
include('db.php');
$_SESSION['competitionId'] = $_GET['competitionId'];
$_SESSION['organisationId'] = $_GET['organisationId'];
<h4>Create your Account</h4>
<form action="login.php" method="post" name="acceptinvite">
name: <input type="text" name="createname"><br>
email: <input type="text" name="createemail"><br>
password: <input type="password" name="createpassword"><br>
<input type="submit" value="Create Account">
</form>
<?php
if (isset($_POST["createname"]) && !empty($_POST["createname"])) {
//define variables
$name = mysql_real_escape_string($_POST['createname']);
$email = mysql_real_escape_string($_POST['createemail']);
$password = mysql_real_escape_string($_POST['createpassword']);
$teamLeader = 0;
$organisationId = mysql_real_escape_string($_SESSION['organisationId']);
$orgName = mysql_real_escape_string($_SESSION['orgName']);
//finish registering the user
$acceptInviteTeam = ("INSERT INTO `users` (`organisationId`, `name`, `email`, `password`, `isTeamLeader`) VALUES ('$organisationId', '$name', '$email', '$password', '$teamLeader')");
$result = mysql_query($acceptInviteTeam) or die (mysql_error());
}
else {
echo "Fill out the form and use the correct credentials";
}
?>

Answer 1

Here's what the problem is.
When you enter the link http://thisapp.com/login.php?competitionId=51da7ed4d686a&organisationId=51d81cab92709 you have organisationId and you save it in the session. But the target of the form is simply login.php. when you submit the form, there is no organisationId in the url, so the session variable gets overwritten by null.
This is the fix:
$_SESSION['competitionId'] = isset($_GET['competitionId']) ? $_GET['competitionId'] : $_SESSION['competitionId'];
$_SESSION['organisationId'] = isset($_GET['organisationId']) ? $_GET['organisationId'] : $_SESSION['organisationId'];
Alternatively you can use an if statement.