Sort on a Playa custom field in ExpressionEngine [HACK]

gistfile1.php

<?php
// Look for this in mod.channel.php (around line 2635):

						case 'custom_field' :
							if (strpos($corder[$key], '|') !== FALSE)
							{
								$end .= "CONCAT(wd.field_id_".implode(", wd.field_id_", explode('|', $corder[$key])).")";
							}
							else
							{
								$end .= "wd.field_id_".$corder[$key];
							}
						break;


// And change to:

						/* change start ---> */
						case 'custom_field' :
							
							if (strpos($corder[$key], '|') !== FALSE)
							{
								$end .= "CONCAT(wd.field_id_".implode(", wd.field_id_", explode('|', $corder[$key])).")";
							}
							else
							{
								$is_playa = FALSE;
								$site_id = ee()->config->item('site_id');
								
								if ( isset ($this->pfields[$site_id][$corder[$key]]))
								{
									if ( $this->pfields[$site_id][$corder[$key]] == 'playa')
									{
										$is_playa = TRUE;
									}
								}
								// do we have a playa field
								if ( $is_playa )
								{
									$end .= "SUBSTRING(wd.field_id_".$corder[$key].", (LOCATE(']', wd.field_id_".$corder[$key].")+1))";
								}
								else
								{
									$end .= "wd.field_id_".$corder[$key];
								}
							}
						break;
						/* <--- change end */