在 Doctrine PHP Symfony 中覆盖 Doctrine_Record (sfDoctrineRecord) 实例方法

My background is in Propel, so I was hoping it would be a simple thing to override a magical getter in a Doctrine_Record (sfDoctrineRecord), but I'm getting either a Segfault or the override method is simply ignored in favor of the one in the superclass.

https://gist.github.com/697008eaf4d7b606286a

class FaqCategory extends BaseFaqCategory
{

  public function __toString()
  {
    return $this->getCategory();
  }

  // doesn't work
  // override getDisplayName to fall back to category name if getDisplayName doesn't exist
  public function getDisplayName() {

    // also tried parent::getDisplayName() but got segfault(!)
    if(isset($this->display_name)) {
      $display_name = $this->display_name;
    } else {
      $display_name = $this->category;
    }

    return $display_name;

  }

}

在 Doctrine_Record 实例上扩展/覆盖方法的正确 Doctrine 方法是什么(通过 sfDoctrineRecord 扩展 Doctrine_Record)?这必须是可行的...还是我应该查看模板文档?