PHP/MySQL nested fetch? - php

Question

I am in the process of making a quick PHP based forum, and each post in a forum will appear under its "parent" post, but slightly more indented.
To get all the posts in that order, I have the following function:
private function getData($pid, $offset)
{
$sql = 'SELECT id, subject, date
FROM post
WHERE forum_id = ? AND parent_id = ?';
$sth = $this->db->prepare($sql);
$sth->bind_param("ii", $this->id, $pid);
$sth->bind_result($id, $subject, $date);
$sth->execute();
$data = array();
while ( $sth->fetch() )
{
$row['id'] = $id;
$row['subject'] = $subject;
$row['date'] = $date;
$row['offset'] = $offset;
//Add this 'parent' post to the data array
$data[] = $row;
//Before moving on to next post, get all its children
$data[] = $this->getData($id, $offset+1);
}
$sth->close();
return $data;
}
This isn't working because I am executing another query before closing and fetching all the data from my current statement handler.
Is there a way to maybe separate the queries so they don't conflict with each other? Or any other way to by-pass this? Or will I simply have to restructure how I get my data?

Answer 1

Fetch all the rows into an array, then loop over them.
$rows = array();
while ( $sth->fetch() ) {
$row['id'] = $id;
$row['subject'] = $subject;
$row['date'] = $date;
$row['offset'] = $offset;
// the cool way is $rows[] = compact('id', 'subject', 'date', 'offset');
$rows[] = $row;
}
$sth->close();
foreach ($rows as $row) {
//Add this 'parent' post to the data array
$data[] = $row;
//Before moving on to next post, get all its children
$data[] = $this->getData($id, $row['offset'] + 1);
}

Answer 2

I will give you a example to show how to do this, this is the table i will use for the example (after just add the forum_id):
CREATE TABLE msgs (
id INT NOT NULL AUTO_INCREMENT,
date DATETIME,
name VARCHAR(100),
message TEXT,
parent_id INT NOT NULL DEFAULT 0
);
Then, with one query do:
$query = mysql_query("SELECT * FROM msgs ORDER BY id");
Some arrays to build the "posts tree", all parent_id = 0 will be root posts:
$all_messages = array(); // Will store all messages
$root_messages = array(); // Will store only the root (or more than one if you allow)
while($row=mysql_fetch_assoc($query)){ // Main loop
$all_messages[$row['id']] = array(
'inner_messages'=>array(),
'date'=> $row['date'],
'name'=> $row['name'],
'message'=>$row['message'],
'id'=>$row['id']
);
if($row['parent_id']=='0'){ // If is a root post
$root_messages[] = &$all_messages[$row['id']];
}else{ // If not a root post, places within parent message
$all_messages[$row['parent_id']]['inner_messages'][] = &$all_messages[$row['id']];
}
}
Now to print, use a recursion:
function writeTree($msgs){
foreach($msgs as $m){
echo '<div>';
echo '<h2>'.$m['name'].' ('.$m['date'].')</h2>';
echo '<div class="text">'.$m['message'].'</div>';
writeTree($m['inner_messages']);
echo '</div>';
}
}
writeTree($root_messages);