$_GET randomly gets unset in if statement - php

Question

I'm sure there is a simple answer to this stupid problem but I have searched high and low and can not figure out why this wont work.
$tutorid = $_GET['userid'];
var_dump($tutorid);
//populate user tutoring subjects
if( isset($_POST['a'])) {
$currentsubjects = get_current_user_subjects( $tutorid );
unset($_POST['a']);
echo json_encode($currentsubjects); return;
}
I have a simple AJAX function that sets $_POST['a'] equal to something. The var_dump($tutorid) properly displays the id from the url. However the $tutorid in the get_current_user_subjects is sending NULL.
If I try a var_dump like this to check $tutorid
$tutorid = $_GET['userid'];
//populate user tutoring subjects
if( isset($_POST['a'])) {
echo json_encode($tutorid); return;
// $currentsubjects = get_current_user_subjects( $tutorid );
// unset($_POST['a']);
// echo json_encode($currentsubjects); return;
}
Then I get NULL. If I hard code in a tutorid in the get_current_user_subjects( $tutorid ) (like add in 15 or something) the function returns data to console.log like expected but using the variable $tutorid stops it completely. I can't figure out why this is happening! Someone please enlighten me.
Here is the AJAX just incase. It works find on other pages so I am assuming the issue is with $_GET
$.ajax({
url: 'profile.php',
method: 'post',
data: "a=true",
dataType: 'json',
success: function (x) {
console.log(x);
},
error: function(a, b, c) {
console.log(a);
console.log(b);
console.log(c);
}

Answer 1

Maybe you can use this method. So you can POST the userid
$.ajax({
url: 'profile.php',
method: 'post',
data: {a: a, userid:userid},
dataType: 'json',
success: function (x) {
console.log(x);
},
error: function(a, b, c) {
console.log(a);
console.log(b);
console.log(c);
}
So in your form before the action. you can set userid in hidden form
<input type="hidden" name="userid" value="<?php echo $userid;?>" />

Answer 2

Save the userId to the session and take it from there. Or pass the userId with the ajax request. I dont think the logic is right in your code, as bsed on the info you have provided. Trying to take the id from $_GET in the requested page while your ajax method is post and no userId is passed with the request, is not right. From my knowledge, you wont have data in the $_GET array if the request to that page is not 'get'. Session provides InterPageCommunication. use session.