How to amend wordpress search so it queries taxonomy terms and category terms?

Question

I want to amend the search so if say I have taxonomy called \"author\" and add a term of \"Ian Rankin\" to a post, if I search for \"Ian Rankin\", I want that post to come up.

Answer 1

You can alter the search query using filter hooks to join the taxonomy tables.

e.g. to also search on the 'author' taxonomy

First join the taxonomy tables

function tax_search_join( $join )
{
  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;
}
add_filter('posts_join', 'tax_search_join');

then find the search term in the taxonomy 'author'

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

and finally group the results by post id to avoid duplicate results because of the join

function tax_search_groupby( $groupby )
{
  global $wpdb;
  if( is_search() )
  {
    $groupby = "{$wpdb->posts}.ID";
  }
  return $groupby;
}
add_filter('posts_groupby', 'tax_search_groupby');