扩展分类法搜索表单以包括自定义帖子类型字段

Question

我有以下内容来创建分类标准的搜索表单，来自＆＃34;考试＆＃34;自定义帖子类型。

我想做的是扩展搜索范围以包含名称为＆＃34; examination_code＆＃34;的字段。来自＆＃34;考试＆＃34;自定义帖子类型。

function buildSelect($tax){
    $terms = get_terms($tax);
    $x = '<select multiple="multiple" name="'. $tax .'[]">';
    $x .= '<option value="">Select '. ucfirst($tax) .'</option>';
    foreach ($terms as $term) {
       $x .= '<option value="' . $term->slug . '">' . $term->name . '</option>';
    }
    $x .= '</select>';
    return $x;
}

搜索表单：

<form method="post" action="<?php bloginfo('url'); ?>/timetable-results/">
<?php  
$taxonomies = get_object_taxonomies('exam'); 
$taxonomies = array_diff($taxonomies, ["language", "post_translations"]);

foreach($taxonomies as $tax){
    echo buildSelect($tax);
}
?>
<input type="submit"/>
</form>

结果页面：

<?php  
$tax_query = array();

foreach ( get_object_taxonomies( 'exam' ) as $tax ) {
    if ( isset( $_POST[ $tax ] ) ) {
        $tax_query[] = array(
            'taxonomy' => $tax,
            'terms' => wp_unslash( ( array ) $_POST[ $tax ] ),
            'field' => 'slug',          
        );
    }
}

$args['tax_query'] = $tax_query;
$paged = (get_query_var('paged')) ? get_query_var('paged') : 1;
$args['paged'] = $paged;  
$the_query = new WP_Query( $args );
var_dump($the_query);

?>