Nested comments in PHP & MySQL

I searched through the forums but couldn’t get an authoritative answer. I want to implement a nested comment structure in a way like this:

<ul>
    <li>This is the parent first comment!
        <ul>
            <li>This is the reply for the first parent comment!
                <ul>
                    <li>This is a reply for the first reply of the parent comment!</li>
                    <li>This is a third reply for the first parent comment!</li>
                </ul>
            </li>
            <li>This is another reply for first parent comment!</li>
        </ul>
    </li>
    <li>This is gonna be parent second comment!
        <ul>
            <li>This is a reply for the second comment!</li>
        </ul>
    </li>
    <li>This is fourth parent comment!</li>
</ul>

The dump for my table is below:

+----+------------------------------------------------------------+--------+
| id | text                                                       | parent |
+----+------------------------------------------------------------+--------+
|  1 | This is the parent first comment!                          |      0 |
|  2 | This is gonna be parent second comment!                    |      0 |
|  3 | This is the reply for the first parent comment!            |      1 |
|  4 | This is another reply for first parent comment!            |      1 |
|  5 | This is a reply for the first reply of the parent comment! |      3 |
|  6 | This is a reply for the second comment!                    |      2 |
|  7 | This is a third reply for the first parent comment!        |      3 |
|  8 | This is fourth parent comment!                             |      0 |
+----+------------------------------------------------------------+--------+

I know how to use mysql_query() and while() loops. A beginner in PHP & MySQL. Please help me out.

Answers:

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Method 1

There are several different ways to store heirarchical data in MySQL. Check out Bill Karwin’s presentation that demonstrates four options.

• Adjacency List
• Path Enumeration
• Nested Sets
• Closure Table

You are using the adjacency list model for storing heirarchical data, but unfortunately this is the hardest model you could choose for querying subtrees.

Your options are:

• Change to a different model.
• Restrict queries to n levels deep.
• Use a stored procedure to query recursively. For more information about this, see Quassnoi’s series of articles – Hierarchical queries in MySQL.

Method 2

I had done something similar for my blogpost. Yet, I just tried out with the same data. When you say nested comments it is better you can use nested functions this way:

function getComments($parent)
{
    # Get the data from SQL.
    # Check if it has nested comments.
    if (hasComments())
        getComments($child); # $child is the ID of the current comment.
}

To make it this way, I have imported your data to MySQL and tried this:

<?php
    mysql_connect('localhost', 'root');
    mysql_select_db('nestedcomments');
    function getComments($parent)
    {
        $res = mysql_query("SELECT * FROM `nestcomm` WHERE `parent` = $parent");
        if (mysql_num_rows($res))
        {
            echo "<ul>n";
            while (($dat = mysql_fetch_array($res)) !== false)
                echo "<li>", $dat["text"], getComments($dat["id"]), "</li>n";
            echo "</ul>n";
        }
        else
            echo ($parent === 0) ? 'No Comments!' : "";
    }
    getComments(0);
?>

As I said before I have used nested functions, and as you asked the output is almost same (without the braces) this way:

<ul>
<li>This is the parent first comment!<ul>
<li>This is the reply for the first parent comment!<ul>
<li>This is a reply for the first reply of the parent comment!</li>
<li>This is a third reply for the first parent comment!</li>
</ul>
</li>
<li>This is another reply for first parent comment!</li>
</ul>
</li>
<li>This is gonna be parent second comment!<ul>
<li>This is a reply for the second comment!</li>
</ul>
</li>
<li>This is fourth parent comment!</li>
</ul>

Hope this helps out.

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0