PHP
<? require('../includes/connect.php');
$interval=130; # Seconds
$entry_id=$_REQUEST['eid'];
$editor_id=$_REQUEST['aid'];
$checkq="SELECT workflow_created_by,workflow_created_on,
NOW()-INTERVAL $interval SECOND,workflow_closed_on,author_name,NOW()
FROM mt_workflow,mt_author WHERE workflow_created_by=author_id
AND workflow_entry_id=$entry_id AND workflow_type=1";
$clearq="DELETE FROM mt_workflow WHERE workflow_entry_id=$entry_id
AND workflow_type=1";
$reserveq="INSERT INTO mt_workflow VALUES (0,$entry_id,$editor_id,1,NULL,
$editor_id,NOW(),NULL,NOW())";
$refreshq="UPDATE mt_workflow SET workflow_closed_on=NOW(),
workflow_created_by=$editor_id WHERE workflow_entry_id=$entry_id
AND workflow_type=1";
$rslt=mysql_fetch_row(mysql_query($checkq));
if($rslt[0]){
if($rslt[0]==$editor_id){
# Me!
$rslt=mysql_query($refreshq) or die(mysql_error());
echo 'OK';
exit;
}
if(Date("Y-m-d-H-i",strtotime($rslt[3]))>=Date("Y-m-d-H-i",strtotime($rslt[2]))){
# Locked
echo 'This article has been locked by '.$rslt[4].' since '.$rslt[1].'.<br/>
(Server time is now '.$rslt[5].', and '.$rslt[4].
' was last seen at '.$rslt[3].'. Any contact within the last '.
$interval.' seconds is considered current.)<br/>
In order to ensure that editing changes are not lost, you will need to
refresh this page in order to edit this article. And, of course, '.$rslt[4].
' will need to be done with it!';
}else{
# Old, so me!
$rslt=mysql_query($clearq) or die(mysql_error());
$rslt=mysql_query($reserveq) or die(mysql_error());
echo 'OK';
}
}else{
# Nothing, so me!
$rslt=mysql_query($reserveq) or die(mysql_error());
echo 'OK';
}
?>
This is the code called as /mt/keepalive.php from the javascript. After ensuring that I can get to the mysql database and gathering my variable, I build a few queries, not knowing yet which ones I'll need. I then execute one, which is this:
SELECT workflow_created_by,workflow_created_on,NOW()-INTERVAL $interval SECOND,workflow_closed_on,author_name,NOW() FROM mt_workflow,mt_author WHERE workflow_created_by=author_id AND workflow_entry_id=$entry_id AND workflow_type=1The table 'mt_workflow' is something I created, and tracks a couple of other things in addition to editing concurrency; hency workflow_type. In this case, I should end up with information about the last person seen editing the article, if any.
If there is no record matching this article ID, we take the outer loop, labeled "Nothing, so me!" There we reserve the slot for the user:
INSERT INTO mt_workflow VALUES (0,$entry_id,$editor_id,1,NULL,$editor_id,NOW(),NULL,NOW())If there is a record, it might be the user's own from a previous call to this page, possibly 30 seconds earlier. If so, we take the first clause, labeled "Me!", and update the timestamp to note that we still have the article open:
Article comments
1 - Aaman
I wish that Ajax book was cheaper:)
Incidentally, is this true AJAX, does the reliance on PHP and SQL not mean a new paradigm, not reliant on XML?
2 - Phillip Winn
It's still XMLHttpRequest, so all three elements of AJAX are present. The PHP and Mysql are, I think, incidental. It could as easily be anything else, or an external webservice, on the "back end."