Paypal ipn integration with php mysql smarty

i'm looking for a easy to go paypal ipn integration script.
What i want is once client make payment, the database should be updated with paypal transaction id.
my sql table which i want to update with paypal transaction id is simple, with fields like
paypal txn id  // to be updated...

How can i achieve this...
if possible give a working code...
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Have the notifications page set.

You need to send a custom var (random number etc) to paypal and save that same custom var to your database

then in your notification page

$key = $_POST['custom'];

$txn_id = $_POST['txn_id'];

then update paypal_txn_id to $txn_id where customkey = $key

there are a number of scripts out there that do this nicley...
AUCKLANDITCommented: thats an example of one I have used before.

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global_expert_adviceAuthor Commented:
okay solution
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