*WordPress* Add search functionality including custom fields

custom-search.php

<?php
/*--------------------------------------*/
/*	Custom Search                       */
/*--------------------------------------*/

/* -------------------------------------*/
/*	1. posts_search                     */
/* -------------------------------------*/
add_filter( 'posts_search', function( $orig_search, $query ){

	if ( $query->is_search() && $query->is_main_query() && ! is_admin() ) :

		global $wpdb;
		$q = $query->query_vars;
		$n = ! empty( $q['exact'] ) ? '' : '%';
		$search = '';
		$searchand = '';

 		if( isset($q['search_terms']) ):
		foreach ( $q['search_terms'] as $term ) :
			$include = '-' !== substr( $term, 0, 1 );
			if ( $include ) {
				$like_op  = 'LIKE';
				$andor_op = 'OR';
			} else {
				$like_op  = 'NOT LIKE';
				$andor_op = 'AND';
				$term     = substr( $term, 1 );
			}
			$like = $n . $wpdb->esc_like( $term ) . $n;
			$search .= $wpdb->prepare( "{$searchand}(($wpdb->posts.post_title $like_op %s) $andor_op ($wpdb->posts.post_content $like_op %s) $andor_op (custom.meta_value $like_op %s))", $like, $like, $like );
			$searchand = ' AND ';
		endforeach;
		endif;

		if ( ! empty( $search ) ) {
			$search = " AND ({$search}) ";
			if ( ! is_user_logged_in() )
				$search .= " AND ($wpdb->posts.post_password = '') ";
		}

		return $search;		
	else :
		return $orig_search;
	endif;

}, 10, 2 );


/* -------------------------------------*/
/*	2. posts_join                       */
/* -------------------------------------*/
add_filter( 'posts_join', function( $join, $query ){

	if ( $query->is_search() && $query->is_main_query() && ! is_admin() ) :
		global $wpdb;
		$join .= " INNER JOIN ( ";
		$join .= " SELECT post_id, group_concat( meta_value separator ' ') AS meta_value FROM $wpdb->postmeta ";
		$join .= " GROUP BY post_id ";
		$join .= " ) AS custom ON ($wpdb->posts.ID = custom.post_id) ";
	endif;

	return $join;
}, 10, 2 );
?>