Custom Taxonomy Example

<?php
/*
 This snippet will create a custom taxonomy, register it to the event CPT, and add a search field to your events search form.
 By Events Manager 5.5.8 the last two functions aren't needed, because EM will automatically register these new taxonomies as searchable within itself.

 For help with adding this for your site, see here - http://wp-events-plugin.com/tutorials/how-to-safely-add-php-code-to-wordpress/
 */

//Create a custom taxonomy.
function my_em_create_custom_taxonomy() {
    $labels = array(
        'name' => 'Grades',
        'singular_name' => 'Grade',
        'search_items' => 'Search Grades',
        'all_items' => 'All Grades',
        'parent_item' => 'Parent Grade',
        'parent_item_colon' => 'Parent Grade:',
        'edit_item' => 'Edit Grade',
        'update_item' => 'Update Grade',
        'add_new_item' => 'Add New Grade',
        'new_item_name' => 'New Grade Name',
        'menu_name' => 'Grade Categories',
    );
    register_taxonomy('grades',array(EM_POST_TYPE_EVENT), array(
        'hierarchical' => true,
        'labels' => $labels,
        'query_var' => true
    ));
}
add_action( 'init', 'my_em_create_custom_taxonomy', 0 );

//Hook into the search form and add the Custom Taxonomy search field.
function my_em_custom_taxonomy_search_form(){
    ?>
    <div class="em-search-category em-search-field">
    <label>Grades</label>
    <?php
    $selected = !empty($_REQUEST['grades']) ? $_REQUEST['grades']:false;
    wp_dropdown_categories( array(
        'hide_empty' => 0,
        'orderby' =>'name',
        'name' => 'grades',
        'hierarchical' => true,
        'taxonomy' => 'grades',
        'selected' => $selected,
        'show_option_none' => 'Choose a grade',
        'option_none_value'=>0,
        'class'=>'em-events-search-grade',
    ));
    ?>
    </div>
    <?php
}
add_action('em_template_events_search_form_footer', 'my_em_custom_taxonomy_search_form');

//Delete everthing below in Events Manager 5.5.8 or later, although this has no negative impact if left here by mistake

function my_em_custom_taxonomy_accepted_search($searches){
    $searches[] = 'grades';
    return $searches;
}
add_filter('em_accepted_searches','my_em_custom_taxonomy_accepted_search',1,1);

function my_em_custom_taxonomy_default_search( $args ){
    if( empty($args['grades']) ) $args['grades'] = false;
    return $args;
}
add_filter('em_events_get_default_search','my_em_custom_taxonomy_default_search');