Automatically sorting custom post type admin area by a custom field

I have created a custom post type to display future events, with the event’s date stored in a custom field (YYYY/MM/DD format). I’d like the admin screen for this custom post type to be automatically sorted by the event date custom field.

Having tried out MikeSchnickel’s excellent tutorial on creating a ‘sort by’ column, I think I’ve worked out that I need to use something similar to the parse_query filter he uses. But I can’t seem to adapt it to my needs,

I’m pretty new to customizing wordpress like this, so some simple guidance would be much appreciated!

Here’s my code to register the custom type post (gs_events), add meta box for the custom field (event_date), and set up custom columns for the admin screen….

add_action('init', 'my_custom_init');

function my_custom_init() {
  $labels = array(
    'name' => _x('Events', 'post type general name'),
    'singular_name' => _x('Event', 'post type singular name'),
    'add_new' => _x('Add New', 'event'),
    'add_new_item' => __('Add New Event'),
    'edit_item' => __('Edit Event'),
    'new_item' => __('New Event'),
    'view_item' => __('View Event'),
    'search_items' => __('Search Events'),
    'not_found' =>  __('No events found'),
    'not_found_in_trash' => __('No events found in Trash'), 
    'parent_item_colon' => ''
  );
  $args = array(
    'labels' => $labels,
    'public' => true,
    'publicly_queryable' => true,
    'show_ui' => true, 
    'query_var' => true,
    'rewrite' => array('slug' => 'events'),
    'capability_type' => 'post',
    'hierarchical' => false,
    'menu_position' => 5,
    'supports' => array('title','editor','thumbnail','comments')
  ); 
  register_post_type('gs_events',$args);
}

register_taxonomy("Location", array("gs_events"), array("hierarchical" => true, "label" => "Cities", "singular_label" => "City", "rewrite" => true));

add_action("admin_init", "admin_init");

function admin_init(){
  add_meta_box("event_date-meta", "Event Date", "event_date", "gs_events", "side", "high");
}

function event_date(){
  global $post;
  $custom = get_post_custom($post->ID);
  $event_date = $custom["event_date"][0];
  ?>
  <label>Date:</label>
  <input name="event_date" value="<?php echo $event_date; ?>" />
  <?php
}

add_action('save_post', 'save_details');

function save_details(){
  global $post;
  update_post_meta($post->ID, "event_date", $_POST["event_date"]);
}

add_action("manage_posts_custom_column",  "events_custom_columns");
add_filter("manage_edit-gs_events_columns", "events_edit_columns");

function events_edit_columns($columns){
  $columns = array(
    "cb" => "<input type="checkbox" />",
    "title" => "Venue",
    "location" => "Location",
    "event_date" => "Date",
  );

  return $columns;
}
function events_custom_columns($column){
  global $post;

  switch ($column) {
    case "event_date":
      $custom = get_post_custom();
      echo $custom["event_date"][0];
      break;
    case "location":
      echo get_the_term_list($post->ID, 'Location', '', ', ','');
      break;
  }
}

And I reckon I need to add some modification of this code from Mike Schnickels’s aforementioned tutorial, but I’m not sure how to implement it in this case…

add_filter( 'parse_query', 'sort_movie_by_meta_value' );
function sort_movie_by_meta_value($query) {
    global $pagenow;
    if (is_admin() && $pagenow=='edit.php' &&
            isset($_GET['post_type']) && isset($_GET['post_type'])=='movie' && 
            isset($_GET['sortby'])  && $_GET['sortby'] !='None')  {
        $query->query_vars['orderby'] = 'meta_value';
        $query->query_vars['meta_key'] = $_GET['sortby'];
    }
}