Function for MY_Model that allows you to do FIND_IN_SET() Ordering via the CodeIgniter Active Record Class.

MY_Model-sort_literal.php

<?php 

/**
 * http://dev.mysql.com/doc/refman/5.1/en/string-functions.html#function_find-in-set
 * 
 * @param field
 * @param first_value, second_value, ...
 */
public function sort_literal() {
	$args = func_get_args();
	$field = $this->db->protect_identifiers(array_shift($args));
	foreach ($args as &$val) {
		$val = $this->db->escape_str(trim($val));
	}
	$set_str = join($args, ',');
	$set_str = str_replace(" ", "", $set_str);

	$orderby_statement = "FIND_IN_SET($field, '{$set_str}')";

	$this->db->ar_orderby[] = $orderby_statement;
	if ($this->db->ar_caching === TRUE) {
		$this->db->ar_cache_orderby[] = $orderby_statement;
		$this->db->ar_cache_exists[] = 'orderby';
	}
	return $this;
}