searching with taxonomy terms in Wordpress

include_terms.php

function document_posts_search_filter( $query ) {
  if ( !is_admin() && $query->is_main_query() ) {
    if ($query->is_search) {
      $tax_args = array( 'relation' => 'OR' );
      // document types taxonomy
      $doctypes = explode(",", get_query_var( 'doctype' ) );
      if ( isset( $_GET['doctype'] ) && $_GET['doctype'] != "" ) {
        $tax_args[] = array(
          'taxonomy' => 'document_type',
          'field' => 'slug',
          'terms' => $doctypes,
          'operator' => 'IN',
        );
      }
      $query->set( 'tax_query', $tax_args );
    }
    $query->set( 'post_type', array( 'document_cpt' ) );
  }
  return $query;
}
add_filter( 'pre_get_posts', 'document_posts_search_filter' );

optional_term_search.php

// http://stackoverflow.com/questions/13491828/how-to-amend-wordpress-search-so-it-queries-taxonomy-terms-and-category-terms
function tax_search_join( $join, $wp_query)
{
  global $wpdb;
  if( is_search() )
  {
    $join .= "
        INNER JOIN
          {$wpdb->term_relationships} ON {$wpdb->posts}.ID = {$wpdb->term_relationships}.object_id
        INNER JOIN
          {$wpdb->term_taxonomy} ON {$wpdb->term_taxonomy}.term_taxonomy_id = {$wpdb->term_relationships}.term_taxonomy_id
        INNER JOIN
          {$wpdb->terms} ON {$wpdb->terms}.term_id = {$wpdb->term_taxonomy}.term_id
      ";
  }
  return $join;
}

function tax_search_where( $where )
{
  global $wpdb;
  if( is_search() )
  {
    // add the search term to the query
    $where .= " OR
    (
      {$wpdb->term_taxonomy}.taxonomy LIKE 'document_tags'
      AND
      " . $wpdb->prepare( "{$wpdb->terms}.name LIKE '%%%s%%'", get_query_var('s') ) . "
    ) ";
  }
  return $where;
}

function tax_search_groupby( $groupby )
{
  global $wpdb;

  if( !is_search() ) {
    return $groupby;
  }

  // we need to group on post ID
  $search_group_by = "{$wpdb->posts}.ID";

  if( preg_match( "/$search_group_by/", $groupby )) {
    // grouping we need is already there
    return $groupby;
  }

  if( !strlen(trim($groupby))) {
    // groupby was empty, use ours
    return $search_group_by;
  }

  // wasn't empty, append ours
  return $groupby . ", " . $search_group_by;
}
add_filter('posts_join', 'tax_search_join', 10, 2);
add_filter('posts_where', 'tax_search_where');
add_filter('posts_groupby', 'tax_search_groupby');

SQL when both are used

// Not unique table/alias: 'wp_term_relationships'
SELECT SQL_CALC_FOUND_ROWS wp_posts.ID
FROM wp_posts 
INNER JOIN wp_term_relationships
ON (wp_posts.ID = wp_term_relationships.object_id) 
INNER JOIN wp_term_relationships
ON wp_posts.ID = wp_term_relationships.object_id 
INNER JOIN wp_term_taxonomy
ON wp_term_taxonomy.term_taxonomy_id = wp_term_relationships.term_taxonomy_id 
INNER JOIN wp_terms
ON wp_terms.term_id = wp_term_taxonomy.term_id 
WHERE 1=1 
AND ( wp_term_relationships.term_taxonomy_id IN (3) )
AND (((wp_posts.post_title LIKE '%melon%')
OR (wp_posts.post_excerpt LIKE '%melon%')
OR (wp_posts.post_content LIKE '%melon%'))) 
AND wp_posts.post_type = 'document_cpt'
AND (wp_posts.post_status = 'publish'
OR wp_posts.post_status = 'acf-disabled'
OR wp_posts.post_status = 'private')
OR ( wp_term_taxonomy.taxonomy LIKE 'document_tags' 
AND wp_terms.name LIKE '%melon%' ) 
GROUP BY wp_posts.ID
ORDER BY wp_posts.post_title LIKE '%melon%' DESC, wp_posts.post_date DESC
LIMIT 0, 20