Cakephp(cakeedc)搜索插件自定义过滤方法

我试图使用cakephp搜索插件，我使用查询方法过滤结果有问题。我创建了一个名为findByLength()的函数，它在$filterArgs数组中声明。我不确定我正在构建的阵列是否正确。当我看sql语句，它看起来甚至没有被调用。什么好主意吗?谢谢!

<?php
// findByLength() is not affecting the sql like expected. Any ideas?
// using http://cakedc.com/downloads/view/cakephp_search_plugin
    public $filterArgs = array(
            array('name' => 'name', 'type' => 'like'),
            array('name' => 'search', 'type' => 'like', 'field' => 'Trail.description'),
            array('name' => 'type','type'=>'string'),
            array('name'=>'dogs_allowed','type'=>'value'),
            array('name'=>'area_id','type'=>'value'),
            array('name' => 'length', 'type' => 'query', 'method' => 'findByLength', 'field' => 'Trail.length'),
            array('name' => 'state_id','field'=>'Area.state_id', 'type' => 'value'),
            array('name'=>'created_by_pt','field'=>'Trail.created_by','type'=> 'value'),
            //array('name'=>'created_by_user','field'=>'Trail.created_by','type'=> 'value'),
 );
    public function findByLength(){
        if(empty($data['Trail']['length'])){
            return array();
        }
        switch($data['Trail']['length']){
            case 0:
                return array('AND'=> array($this->alias.'.length >='=> $data['Trail']['length'],
                                                                     $this->alias.'.length <'=> $data['Trail']['length'] + 3)
                                );
            break;
            case 3:
                return array('AND'=> array($this->alias.'.length >='=> $data['Trail']['length'],
                                                                     $this->alias.'.length >'=> $data['Trail']['length'] + 3)
                                );
            break;
            case 6:
            return array('AND'=> array($this->alias.'.length >='=> $data['Trail']['length'],
                                                                 $this->alias.'.length <'=> $data['Trail']['length'] + 4)
                            );
            break;
            case 10:
            return array('AND'=> array($this->alias.'.length >='=> $data['Trail']['length'])
                            );
            break;
        }
    }
?>