AJAX throws error 500 only when PHP function is empty - php

Question

I'm completely puzzled to why this happens, I've been messing on this for a few hours and I'm going crazyyyy! I am trying to update my DB when a checkbox is toggled on or off. The success response works if my PHP function I'm calling is empty, but fails whenever I add PHP. Note I'm on Laravel 3, and I've tried enabling or disabling CSRF filtering, no luck.
My JS:
$seenTD = $('td.seen_by_user');
$seenTD.each(function() {
$this = $(this);
var $seenLabel = $this.find('label');
var $seenInput = $this.find(':checkbox');
$seenInput.change(function() {
var _csrf = $('input[name="csrf_token"]').val();
var chkName = $(this).attr('name');
var checkVal = $(':checkbox[name='+chkName+']').prop('checked'); //true or false
var id = $this.find('input[name="reminder_id"]').val();
$.ajax({
url: 'update',
type: 'POST',
data: 'seen='+checkVal+'&reminder_id='+id+'&csrf_token='+_csrf,
success: function(data) {
console.log(data);
if($seenInput.is(':checked')) {
$seenLabel.removeClass('unchecked').addClass('checked');
$seenLabel.find('span').text('Oui');
}
else {
$seenLabel.removeClass('checked').addClass('unchecked');
$seenLabel.find('span').text('Non');
}
}
});
});
});
My PHP
public function post_update() {
$request = Request::instance();
$content = $request->getContent();
$id = $content['id'];
$seen = $content['seen'];
if($seen == 'true') {
$seen = 1;
}
if($seen == 'false') {
$seen = 0;
}
DB::table('reminders')->where('id', '=', $id)->update(
array(
'seen_by_user' => $seen
));
}

Answer 1

For the sake of maybe helping someone, as this is my first working AJAX, I'll explain how I got it to work, as well as supply working code. I'm not claiming this is the best way to do it, so if anyone has their word to say, don't hesitate :)
There were multiple issues, from Javascript insconsistency returning the row ID I needed for the database update, to the PHP function, and the way I was grabbing the POST data.
To get it to work, I played on Fiddler, retrieved the error message that Laravel throws at me. And I could debug from there :)
My working code is :
JS:
$('td.seen_by_user :checkbox').change(function() {
$this = $(this);
var $label = $this.siblings('label');
var id = $this.attr('data-id');
var _csrf = $this.siblings('input[name="csrf_token"]').val();
var value = $this.prop('checked');
$.ajax({
url: 'update',
type: 'POST',
data: {"seen_by_user": value, "id": id, "csrf_token": _csrf},
success: function(data) {
if($this.is(':checked')) {
$label.removeClass('unchecked').addClass('checked');
$label.find('span').text('Oui');
}
else {
$label.removeClass('checked').addClass('unchecked');
$label.find('span').text('Non');
}
}
});
});
PHP
function post_update() {
$id = $_POST['id'];
$seen = $_POST['seen_by_user'];
if($seen == 'true') {
$seen = 1;
}
if($seen == 'false') {
$seen = 0;
}
$update_reminder = DB::table('reminders')->where('id', '=', $id)->update(
array('seen_by_user' => $seen));
}
And my HTML (Blade Template from Laravel, where {{ }} brackets are simply echo's, and #foreach is a )
#foreach ($reminders as $reminder)
...
<td class="seen_by_user">
<form class="ajax" action="update" method="POST">
{{ Form::token() }}
{{ Form::checkbox('seen_'.$reminder->id, 1, $reminder->seen_by_user, array('id' => 'seen_'.$reminder->id, 'data-id' => $reminder->id)) }}
<label class="seen {{ ($reminder->seen_by_user == 1 ? 'checked' : 'unchecked' ) }}"for="{{ 'seen_'.$reminder->id }}"><i class="read"></i><span>{{ ($reminder->seen_by_user == 1 ? 'Oui' : 'Non') }}</span></label>
</form>
</td>
...
#endforeach

Answer 2

data should be an object like this
data: {"seen": checkVal, "reminder_id": id, "csrf_token": _csrf},
The $.ajax method will take care of the presentation and transmission.