how to stop items with the same ID being added twice in a session?

Question

A quick questions about sessions, I have a session with the following code

<?php
session_start();
$_SESSION['event_orders'][] = $_POST['event_id'];
?>

problem is once I add an item to the session, it can still re-add it again, therefore duplicating it.

How would one preform a check, something like "if ID exists in session, show (remove) instead of (add) button"?

Answer 1

Use in_array function:

<?php
session_start();

if(!in_array($_POST['event_id'], $_SESSION['event_orders'])) {
    $_SESSION['event_orders'][] = $_POST['event_id'];
}
?>