class Customer extends DataObject {
   
   public static $db = array(
[...]
   );
   
   public static $indexes = array(
      'Email' => 'unique'
   );
   
   public static $has_one = array(
      'CustomerGroup' => 'CustomerGroup'
   );
   
   public static $summary_fields = array(
      'Name' => 'Name',
      'Telephone' => 'Telephone',
      'Email' => 'Email',
      'Created' => 'CreatedText'
   );
   
   public static $casting = array("CreatedText" => "Text");
   
public function CreatedText() {
return $this->Created;
}

class crmAdmin extends ModelAdmin {

   public static $menu_title = 'Customer Relationship Manager';
   public static $url_segment = 'crm';
   public static $managed_models = 'CustomerGroup';

[...]