adds meta query on Wordpress search

gistfile1.aw

/**
 * adds meta values on search query
 *
 * @param object $query
 *
**/
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 params like a specific 'post_type'
		// $query->set('post_type', 'project');
	};
}
add_filter( 'pre_get_posts', 'custom_search_query');