Creating a tiered commenting system (efficiently with PHP and MySQL [1 table]) - php

Question

I would like to have a comment section with replies to comments. The replies will only go one level. For example.
Parent Comment
-- Here is a reply
-- Here is another reply
-- It won't go further than this one tier
My MySQL looks like this:
comment_id, comment, parents_id
if parents_id is 0, it is the parent. if it has a number, that number will correspond to the comment_id, as it will be its child.
now, i've done this crappy code below, but it seems the second loop messes it up and only displays the first div correctly with its children. i believe it is because i'm calling mysql_fetch_row twice...
$query_show_comments = "SELECT * FROM article_comments WHERE article_id = '$article_id'";
$results_show_comments = mysql_query($query_show_comments);
$num_rows_comments = mysql_num_rows($results_show_comments);
for ($i = 0; $i < $num_rows_comments; $i++) {
$comment = mysql_fetch_row($results_show_comments);
echo "<p>comment_id: $comment[0]</p>";
if ($comment[5] == 0) {
echo <<<_HTML
<div class="dispArticle">
<p><strong>Commenter Name commented # 11/22/10 10:10:10pm</strong></p>
<p>$comment[2]</p>
_HTML;
for ($j = 0; $j < $num_rows_comments; $j++) {
$replies = mysql_fetch_row($results_show_comments);
if ($replies[5] > 0 AND $replies[5] == $comment[0]) {
echo <<<_HTML
<div class="comment"><p><strong>Reply Name replied # 11/22/10 10:10:10pm</strong></p>
<p>child_id: $replies[0]</p>
<p>parent_id: $comment[0]</p>
<p>$replies[2]</p>
</div>
<br />
_HTML;
}
}
}
echo "</div>";
}
Been searching for hours and this is what I've found.
Use multiple tables (would like to keep it in one table so less queries)
Use multiple queries (same as above)
Feed into an array first then sort it all out (what if the comments are long and there are a lot? I just did a query AND had to do more server side processing of feeding it into an array, sorting then displaying...)

Answer 1

The problem is that mysql_fetch_row() will always fetch the next row returned by the query, and that could be in any order. For what you are doing to work, you would need a post to be followed immediately by its child comments every time. This is a shaky solution, so I would suggest you use #3 as it is really the same thing as what you are doing.
I also have a couple of suggestions: use mysql_fetch_assoc() over mysql_fetch_row() and use the names of the columns rather than their numbers as this makes the code much more readable and easier to use. You will have to change your query to order by the ascending parent ID to ensure that all parents are set first. Then:
$query = "query";
$result = mysql_query($query);
$comments = array();
while ($row = mysql_fetch_assoc($result)) {
if ($row['parent_id']) {
$comments[$row['parent_id']]['children'][] = $row;
}
else {
$row['children'] = array();
$comments[$row['comment_id']] = $row;
}
}
Now all of the children are associated with parents. Just iterate through the array.

Answer 2

It's not too hard. You should store all comments in one table and have parent_id
parent_id of 0 means it's a comment, parent_id > 0 would point to id of a message in the same table for which it's a reply.
You would also have article_id, just like in your current example.
The trick you need is to do just one SQL select but reference the same table twice.
You sql will be something like this:
SELECT
M.id as id,
M.id as com_mid,
M.post_subject as com_subject,
M.message_body as com_body,
M2.id as rpl_mid,
M2.post_subject as rpl_subject,
M2.message_body as rpl_body,
M2.parent_id
FROM
MESSAGES AS M
LEFT JOIN MESSAGES as M2 on M2.parent_message_id = M.id
WHERE M.article_id = :aid
AND M.parent_id = 0
ORDER BY com_mid ASC,
rpl_mid ASC
Then once you get result of this sql, you will easily figure out how to handle the result array to display messages and replies

Answer 3

You need a second query. Here's an example TRYING to use your code.
$query_show_comments = "SELECT * FROM article_comments WHERE article_id = '$article_id'";
$results_show_comments = mysql_query($query_show_comments);
$num_rows_comments = mysql_num_rows($results_show_comments);
for ($i = 0; $i < $num_rows_comments; $i++) {
$row_comment = mysql_fetch_row($results_show_comments);
echo "<p>comment_id: $row_comment[0]</p>";
if ($row_comment[5] == 0) {
echo <<<_HTML
<div class="dispArticle">
<p><strong>Commenter Name commented # 11/22/10 10:10:10pm</strong></p>
<p>$row_comment[2]</p>
_HTML;
$query_show_replies = "SELECT * FROM article_comments WHERE parent_id = '$article_id'";
$result_replies = mysql_query($query_show_replies);
while( $row_reply = mysql_fetch_row($results_show_comments) ) )
echo "
<div class=\"comment\"><p><strong>Reply Name replied # 11/22/10 10:10:10pm</strong></p>
<p>child_id: $row_reply[0]</p>
<p>parent_id: $row_reply[1]</p>
</div><br />
";
}
}
echo "</div>";
}
You're doing several things in your code that I don't like to do, not saying it can't be don't that way. My advice is to take a more advanced approach to architecting your web applications:
Use while() loops when reading data from queries, it's more error tolerant
don't use the "echo <<<" blocks because it makes code harder to read
technically speaking, you'll want to use htmlspecialchars on all output to a web page, so the <<< shouldn't be used anyways
better yet, use a template system to extricate your markup (view) from your PHP, conside Smarty because it's easy even if performance isn't quite stellar
in fact, while you're at it, consider abstracting your data code into a separate layer
no matter how you get the data, you shouldn't rely on indexed fields when you're using a SELECT *.. because the order could change. What I mean is, instead of using $comment[0] or $comment[1], use $comment['id'] or htmlspecialchars($comment['text'])