php form will not submit unless the checkbox is ticked - php

Question

my form is unable to submit unless the checkbox is ticked, I am really unsure as to why this is.
further, if the checkbox is ticked it fails to update the database, there is no issue with the function I am using or the query as i have checked that directly on the db.
Any help would be hugely appreciated, and please feel free to ask any questions if there is anymore information i can give
<?php
include 'core/init.php';
protect_page();
include 'includes/overall/header.php';
$page = $_GET['page'];
$email = $_GET['user'];
$p_id = project_id_from_project_name($page);
$supervisor = supervisor_from_email($email, $p_id);
$user_id = user_id_from_email($email);
?>
<h1>Add A User to the Project</h1>
<?php
if (isset($_GET['form_submit']) === true && empty($_GET['form_submit']) === false) {
echo 'You\'re user has been added successfully!<br /><br />';
echo 'Please click here to return to Your Projects';
} else {
if (empty($_POST) === false && empty($errors) === true) {
$page = $_GET['page'];
$p_id = project_id_from_project_name($page);
$supervisor_update = ($_POST['supervisor'] == 1) ? 1 : 0;
$update_project_member_data = array(
'project_id' => "$p_id",
'project_name' => "$page",
'project_member_id' => "$user_id",
'supervisor' => "$supervisor_update"
);
update_project_member_data($p_id, $update_project_member_data);
header('Location: update_user.php?page=' . $page .'&user=' . $email .'&form_submit=1');
exit();
} else if (empty($errors) === false) {
echo output_errors($errors);
}
?>
<form action="" method="post">
<ul>
<li>
Email Address: <?php echo $email ?>
</li>
<li>
Set user as Supervisor?<br />
<input name="supervisor" type="checkbox" <?php if ($supervisor == 1) {?> checked="checked"<?php }?>/>
</li>
<li>
<input type="submit" value="Update User">
</li>
</ul>
</form>
<?php
}
include 'includes/overall/footer.php'; ?>

Answer 1

I believe the problem is with the condition you have:
empty($_POST) === false
Since your form is very basic and only has the one input. The $_POST array is only populated with values when that input is checked. Unchecked it doesn't pass any values in the $_POST array. Normally, the submit button would pass a value, but since you didn't have the "name" attribute on there, it doesn't.
You can either try adding the name attribute to the submit button or just add a hidden value inside the FORM element such as:
<input type="hidden" name="action" value="submitted" />

Answer 2

I think what is happening here is that there is no data to post if you do not check the box. You can check for the request method, $_SERVER['REQUEST_METHOD'] instead of empty($_POST).
edit: to clarify, the post happens but the if condition evaluates to false