Select All not working in a WordPress search filter

by

Couple of notes:

  1. Your form action is incorrect: <form method="get"
    action="http://www.adoptapet.ie/archive-farm/">    . The page is <form
    method="get" action="http://www.adoptapet.ie/archive-farms/">

  2. You should reorder your argument list for
    adopt_custom_taxonomy_dropdown(). As written, most of your
    arguments have default values and can be omitted when the function
    is called, except that as written argument five doesn’t have a
    default so you can’t in practice omit two, three, and four. Move
    $name to the front– much better usability.

    adopt_custom_taxonomy_dropdown( $taxonomy, $name, $orderby = 'date', $order="DESC", $limit="-1", $show_option_all = null, $show_option_none = null )
  3. Don’t use query_posts(), ever. It clobbers the main query and can
    cause numerous problems.
  4. While I have not edited the code into the suggestions below, you
    should not ever use user supplied data like $_GET without
    sanitizing it. $_GET and $_POST are not safe.

I think your problem is mostly a logic issue. This…

isset($_GET["farm-type"]) && isset($_GET["location-farms"])

…. is always going to be true. $_GET["farm-type"] and $_GET["location-farms"] are always going to be set when your form submits, even if they are empty. You should be using !empty() instead.

And you can clean up this code a lot:

if (!empty($_GET["farm-type"])){
  $farm_type = $_GET["farm-type"];
  $myquery['tax_query'][] = 
    array(
      'taxonomy' => 'farm-type',
      'terms' => array($farm_type),
      'field' => 'slug',
    );
}

if (!empty($_GET["location-farms"])){
  $farm_location = $_GET["location-farms"];
  $myquery['tax_query'][] = 
    array(
      'taxonomy' => 'location-farms',
      'terms' => array($farm_location),
      'field' => 'slug',
    );
}

if (!empty($myquery)) {
  $q = new WP_Query($myquery); // instead of wp_query()
  var_dump($q);
}

And you probably want an AND relationship between your two components.

if (!empty($myquery)) {
  if (1 < count($myquery['tax_query'])) {
    $myquery['tax_query']['relation'] = 'AND';
  }
  $q = new WP_Query($myquery);
  var_dump($q->request); // debug
}

Now, if you pass an empty string for your “Select All” option instead of a number, I believe you should get the results you are looking for.