class SelectModelAdmin extends ModelAdmin {
   public static $managed_models = array(
      'SelectModel'
   );
   static $url_segment = 'selectadmin';
   static $menu_title = 'Select Admin';
}
class SelectModel extends DataObject {
   static $db = array('Name' => 'Text');
   static $searchable_fields = array('Name');
}
class Page extends SiteTree {
   static $has_one = array(
      'Select' => 'SelectModel',
   );
   function getCMSFields() {
      $fields = parent::getCMSFields();
      $select = new DropdownField('SelectID', 'Select', DataObject::get('SelectModel')->map('ID','Name'));
      $fields->addFieldToTab('Root.Content.Main', $select, 'Content');
      return $fields;
   }
}