two users updating same record

[rohithreddyk]

Dont know if the solution is particular to PHP..But wanted to post here anyway coz I am developing the site in PHP..

 

 

I am doing a website where users can update the records in edit.php page..

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Problems is...suppose two users have opened the edit.php at the same time.. suppose the comments field is balnk at first. Now user1 enters "hi..this is SAM" in the comments field and clik submit button. Database is updated with that field. Now user2, unknowing that user1 added some comment, enters "hi this is MARK" in the comments field and clicks submit button.. now the comment entered by user1 is lost.. i want the user2 to get a notification like "some other user already updated the comments field after you opened the page".."do you want to continue"? if he hits Ok update it.. if he hits cancel dont update

[BobcatM]

If I follow you right, you are just wanting to have one comment show up at a time, and only one row in the database...

 

When someone opens the page run a query and check the ID field of the row or something of that nature.

 

Then when the user hit's submit you could run another query that checks if the ID is equal to the same ID as before, if so contiue with the posting, if not echo out "do you want to continue"?

[roopurt18]

You should add timestamp columns to your table.  I like to call mine created_tm and modified_tm.  Each time you insert you set them both equal to now(), or the current time.  From then on each time you update one you set modified_tm equal to now(), or the current time.  This is best done with a trigger so you don't have to program it in your application code.

 

When you present data to the user, include an:

<input type="hidden" name="modified_tm" value="<?php echo $row->modified_tm;?>" />

<input type="hidden" name="primary_key" value="<?php echo $row->primary_key;?>" />

 

Then in your processing script you can do something like:

$moditm = escape_user_input( $_POST['modified_tm'] );

$pk = escape_user_input( $_POST['primary_key'] );

$count = "select count(*) from table where primary_key={$pk} and modified_tm>{$moditm}";

if( $count > 1 ) {

  // record has been updated since user first saw it, so prompt

}else{

  // record has NOT been updated since user first saw it, so update

}

 

That's pseudo code to outline the basic design so don't copy and paste it and expect it to work.  And if you don't want the user to be able to manipulate the hidden fields, then don't send them to the client as hidden fields but instead store them in a session or similar mechanism.