How to Extend WordPress Search to Include Custom Post Meta

This snippet will allow you to extend the WordPress search function to include custom post meta.

Instructions
Add the following code to your functions.php

<?php
   function custom_search_query( $query ) {
      if ( !is_admin() && $query->is_search ) {
         $query->set('meta_query', array(
            array(
               'key'    => '__meta_key__',
               'value'  => $query->query_vars['s'],
               'compare' => 'LIKE'
            )
         ));
         // you can add additional parameters like a specific 'post_type'
         // $query->set('post_type', 'project');
      };
   }
   add_filter( 'pre_get_posts', 'custom_search_query');
?>