cakephp中扩张自定义验证规则

cakephp中扩展自定义验证规则
  在CAKEPHP中,有多达26条验证规则可以用,详细的见这里:
http://book.cakephp.org/view/1181/Adding-your-own-Validation-Methods#!/view/1152/Core-Validation-Rules

但如何扩展自定义呢?比如一个例子中,只对管理员用户要校验输入用户名,普通用户不用
(一个很极端的例子),可以这样做:
class User extends AppModel {  
  var $name = 'User';  
  var $validate = array(
         'name' => array('notempty' =>
array('rule' => array('notempty'),          
      'message' => 'Please enter first name',
......

.......
     'username' => array('custom' =>
    array('rule' => array('validateDependentFields'),    
            'message' => 'Please enter height',
这里对username使用自定义的方法,定义一个方法validateDependentFields去校验

方法为:
 

function validateDependentFields($field){  
   $passed=true; 
    switch(true){     
    case array_key_exists('username',$field):    
         if(  $this->data['User']['user_type_id']==1 and (!isset($this->data['User']['username']) or empty($this->data['User']['username'])) )
{               
  $passed=false;      
       }
else{      
           $passed=true;           
  }      
   break;      
   case array_key_exists('class_of',$field):       
      if(  $this->data['User']['user_type_id']==1 and (!isset($this->data['User']['class_of']) or empty($this->data['User']['class_of'])) )
{   
              $passed=false;    
        
 }else
{           
      $passed=true; 
            }      
   break;  
   }     
return $passed; 
}