Using pre_get_posts to rewrite search query to display posts from multiple taxonomies

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This seems like it should be straightforward, but I’m stuck on it!

If a user searches for ‘alice’, I would like to show them all posts with the custom taxonomy terms of ‘bob’ and ‘carol’, regardless of if those posts contain the string ‘alice’ in them or not.

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I’m able to set the query’s tax_query so that it only shows posts with ‘bob’ and ‘carol’ as terms, but I can’t reset the actual search query so that it is showing all posts, not just posts with ‘alice’ in them.

This is the filter I’m using to change the tax_query: 

if ( !$query->is_search )
    return $query;

$taxquery = array(
    'relation' => 'OR',
    array(
        'taxonomy' => 'people',
        'field' => 'slug',
        'terms' => array( 'bob' ),
    ),
    array(
        'taxonomy' => 'people',
        'field' => 'slug',
        'terms' => array( 'carol' ),
    )
);

$query->set( 'tax_query', $taxquery );
return $query;

but using this to set the search query doesn’t work: 

$queryvars = array(
        's' => ''
);
$query->set( 'query_vars', $queryvars );
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1 comment

  1. It does’t work because you can’t use set to change all query vars. Simplest way to do the trick is set 's' to an empty string:

    add_action( 'pre_get_posts', function( $query ) {

  if ( ! is_admin() && $query->is_main_query() && $query->is_search() ) {
    $taxquery = array( ... );
    $query->set( 'tax_query', $taxquery );
    $query->set('s', '' );
  }

});

    In this way, WordPress will still consider the request a search, so the search.php template will be used to show results and if you call is_search() the result will be TRUE.

    If you want that WordPress will not consider anymore the request a search, you need to also manually unset $query->query_vars['s'] and set $query->is_search to false:

    add_action( 'pre_get_posts', function( $query ) {

  if ( ! is_admin() && $query->is_main_query() && $query->is_search() ) {
    $taxquery = array( ... );
    $query->set( 'tax_query', $taxquery );
    $query->set('s', '' );
    unset( $query->query['s'] );
    $query->is_search = FALSE;
  }

});

    Doing that, WordPress will not anymore consider the request a search, and will use index.php as template.

    If you want to use another template, e.g. taxonomy.php you need to use 'template_include' filter:

    add_action( 'pre_get_posts', function( $query ) {

  if ( ! is_admin() && $query->is_main_query() && $query->is_search() ) {
    $taxquery = array( ... );
    $query->set( 'tax_query', $taxquery );
    $query->set('s', '' );
    unset( $query->query['s'] );
    $query->is_search = FALSE;
    add_filter( 'template_include', function() {
      return locate_template( 'taxonomy.php' )
    }, 0 );
  }

});