Definition and usage skills of smarty custom resources

<?php
// put these function somewhere in your application
function db_get_template ($tpl_name, &$tpl_source, &$smarty_obj)
{
 // do database call here to fetch your template,
 // populating $tpl_source
 $sql = new SQL;
 $sql->query("select tpl_source
   from my_table
   where tpl_name=&#39;$tpl_name&#39;");
 if ($sql->num_rows) {
 $tpl_source = $sql->record[&#39;tpl_source&#39;];
 return true;
 } else {
 return false;
 }
}
function db_get_timestamp($tpl_name, &$tpl_timestamp, &$smarty_obj)
{
 // do database call here to populate $tpl_timestamp.
 $sql = new SQL;
 $sql->query("select tpl_timestamp
   from my_table
   where tpl_name=&#39;$tpl_name&#39;");
 if ($sql->num_rows) {
 $tpl_timestamp = $sql->record[&#39;tpl_timestamp&#39;];
 return true;
 } else {
 return false;
 }
}
function db_get_secure($tpl_name, &$smarty_obj)
{
 // assume all templates are secure
 return true;
}
function db_get_trusted($tpl_name, &$smarty_obj)
{
 // not used for templates
}
// register the resource name "db"
$smarty->register_resource("db", array("db_get_template",
     "db_get_timestamp",
     "db_get_secure",
     "db_get_trusted"));
// using resource from php script
$smarty->display("db:index.tpl");
?>