Hierarchy commenting system php

Question

i want to do discus/reddit/ like commenting system, i have an "id_answer" (set to 0 by defaut) field in my comment database and when user answer to another comment this field is the "id" of the parent comment.

I have the comments of the thread in an array but i dont know how to filter filter each loop for get something like this :

comment lvl 1 ($array[id_answer] is 0)

------- comment lvl 2 ($array[id_answer] is id_of_level_one_comment)

--------------- comment lvl 3 ...

Answer 1

Use three fields in your database;

• "id", unique for each comment
• "parent_id", which is either 0 (top level comment) or the "id" of the parent comment
• "thread_id", which is the id of whatever you are commenting on

Let's say you want to show the comment tree for your news article with id "123"

When selecting from mysql, select everything with this thread_id:

SELECT id, parent FROM comments WHERE thread_id = 123

Then you should pre-parse your array to give the child comments to their parents, and use a recursive display to show each comment and its child list.

For exemple:

// getting the comments from mysql, I'm obviously not bothering
//   to check the return value, but in your code you should do it
$result = mysqli_query("SELECT id, parent FROM comments WHERE thread_id = 123");

$comments = array();
while ($row = mysqli_fetch_array($result)) {
  $row['childs'] = array();
  $comments[$row['id']] = $row;
}

// This is the array you get after your mysql query
// Order is non important, I put the parents first here simply to make it clearer.
/*
$comments = array(
    // some top level (parent == 0)
    1 => array('id' => 1, 'parent' => 0, 'childs' => array()),
    5 => array('id' => 5, 'parent' => 0, 'childs' => array()),
    2 => array('id' => 2, 'parent' => 0, 'childs' => array()),
    10 => array('id' => 10, 'parent' => 0, 'childs' => array()),
    // and some childs
    3 => array('id' => 3, 'parent' => 1, 'childs' => array()),
    6 => array('id' => 6, 'parent' => 2, 'childs' => array()),
    4 => array('id' => 4, 'parent' => 2, 'childs' => array()),
    7 => array('id' => 7, 'parent' => 3, 'childs' => array()),
    8 => array('id' => 8, 'parent' => 7, 'childs' => array()),
    9 => array('id' => 9, 'parent' => 6, 'childs' => array()),
);
*/

// now loop your comments list, and everytime you find a child, push it 
//   into its parent
foreach ($comments as $k => &$v) {
  if ($v['parent'] != 0) {
    $comments[$v['parent']]['childs'][] =& $v;
  }
}
unset($v);

// delete the childs comments from the top level
foreach ($comments as $k => $v) {
  if ($v['parent'] != 0) {
    unset($comments[$k]);
  }
}

// now we display the comments list, this is a basic recursive function
function display_comments(array $comments, $level = 0) {
  foreach ($comments as $info) {
    echo str_repeat('-', $level + 1).' comment '.$info['id']."\n";
    if (!empty($info['childs'])) {
      display_comments($info['childs'], $level + 1);
    }
  }
}

display_comments($comments);

This give the following result:

- comment 1
-- comment 3
--- comment 7
---- comment 8
- comment 5
- comment 2
-- comment 6
--- comment 9
-- comment 4
- comment 10

I leave the ORDER BY and such to you, as it should not pose any problem.