Try using this code in your model class (perhaps in AppModel):
function get_sql_insert_id() {
$db =& ConnectionManager::getDataSource($this->useDbConfig);
return $db->lastInsertId();
}
Caveat emptor: MySql's LAST_INSERT_ID() function only works on tables with an AUTO_INCREMENT field (otherwise it only returns 0). If your primary key does not have the AUTO_INCREMENT attribute, that might be the cause of your problems.