Description :

               This method returns the primary key of the object. If this one is non-existent, “NULL” will be returned.

Value of return :

               Turn over the value of the primary key of the object.
               Turn over “NULL” if the value of the primary key of the object is null.

The following example posts the primary key of a product :

<?php 

   //total instanciation 
   include_once( 'phpsimpledb.class.php' ); 
   Global $oBDD; 
   $oBDD = new PHPSIMPLEDB(); 
   
   //recovery of the product
   $oProduit = $oBDD->getObject( "produits" ); 
   $oProduit->load( 13 ); 
   
   //display the primary key
   print( "Key : ".$oProduit->getData_key() ); 

?>