How to tree strcture function in PHP for OOPS? - php

Question

I am creating a comment and reply system in PHP using the tree concept.
I have created a comment table in my database -
CREATE TABLE `comments` (
`cm_id` int(11) NOT NULL,
`cm_message` text NOT NULL,
`postid` int(11) DEFAULT NULL,
`user_id` int(11) NOT NULL,
`created` datetime NOT NULL,
`parentid` int(11) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
As you can see, I have contained parent id and comment id with post id.
My tree function
function fetchCategoryTree($parentid = 0,$user_tree_array = '') {
global $db;
global $postid;
if (!is_array($user_tree_array))
$user_tree_array = array();
$stmt = $db->prepare('SELECT
comments.cm_message, comments.cm_id,comments.parentid,comments.created,users.username, users.image
FROM comments
INNER JOIN users ON comments.user_id = users.user_id
WHERE comments.postid=:postid AND parentid =:parentid ORDER by comments.cm_id DESC');
$stmt->execute(array('parentid' => $parentid,
'postid' => $postid
));
if($stmt->rowCount() > 0) {
while ($row = $stmt->fetchObject()) {
$user_tree_array[] = array("cm_id" => $row->cm_id,"image" => $row->image,"parentid" => $row->parentid,"username" => $row->username,"created" => $row->created, "cm_message" =>$row->cm_message);
$user_tree_array = fetchCategoryTree($row->cm_id, $user_tree_array);
}
}
return $user_tree_array;
}
Calling a function
$categoryList = fetchCategoryTree();
It's working but,
As you can see I have made a global postid in the function.
if I give the postid inside
$categoryList = fetchCategoryTree($postid);
and change the function look like -
function fetchCategoryTree($postid) {
global $db;
$parentid = 0;
$user_tree_array = '';
}
then it doesn't work.
I want to convert it to OOPS class and method but it's not working like this.
The main points are here -
I am inserting comments and replies in the same table.
I am fetching comments and replies by postid using while loop on the same page -
like -
post 1
comments for post 1
with reply
post 2
comments for post 2
with reply
post n
comments for n post
with reply n
What are the best ways to do that in OOPS?
class and method
How can I use postid at the calling time without any errors?