grails通过Ajax实现select标签的级联

在grails通过选择select不同的option，通过Ajax查询数据库中的值，返回Json类型的结果，实现页面标签的无刷新级联。
1.页面代码，在id为type.id不同的选择返回不同的值到id为brand的select中。

 <tr> <td valign="top" class="name">
                           <label for="type">设备类型</label>
                    </td>
                      <td>
<select id="type.id" name="type.id" onchange ="setPinPai(this.options[this.selectedIndex].value)">
<g:each in="${purCategoryList}"status="i"var="purCategoryIn">         
<option value="${purCategoryIn.id}">${purCategoryIn.name}</option>
                            </g:each>                                     
                      </select><font color = "red">*</font>
                              </td>
                             </tr>
                             
                             <tr class="prop">
                              <td valign="top" class="name">
                                 <label for="brand">设备品牌:</label>
                              </td>
                              <td>
                                 <select id ="brand" name="brand">

        <g:each in="${brandList}" status="i" var="brand">     
         <option value="${brand.name}">${brand.name}</option>
                            </g:each>                                       
                        </select><font color = "red">*</font>

2.js进行处理，导入prototype类库，发送Ajax异步请求，获得返回的json类型的值，然后加入到id为brand的select中。

 <g:javascript library="prototype" />
        <script language="JavaScript" type="text/javascript">

          function setPinPai(xiaolei){
            var baseUrl = "${createLink(controller:'purList', action:'getJson')}"
            var url = baseUrl + "?bigId=" +(xiaolei)
            
            new Ajax.Request(url, {
              method: 'get',
              asynchronous: true,
              onSuccess:function(req) {update(req.responseText, 'pinpaiMess')}
            })
          }

          function update(json, mess){
          //  alert(json);
              var cjxx = eval( "(" + json + ")" )
              //删除所有的值
              document.getElementById("brand").options.length=0;

              for(var i = 0;i<cjxx.length;i++){     
                var pinPaiText = cjxx[i].name;
                var pinPaiValue = cjxx[i].name;  
                document.getElementById("brand").options.add(new Option(pinPaiText,pinPaiValue));
              }
          }
 </script>

3.controllor中的处理，通过传入的id好进入数据库进行查询，然后返回json结果。

    def getJson ={
//处理已经遗留的数据库
//        println params.id+" getJson""
//        Sql sql = new Sql(dataSource)
//        def com_id = params.id
//        def xiaoleiStr = " select p.name as xiaolei,p.pur_big_cate_id as xiaoleiid from pur_category p "
//        if(com_id!=null&&com_id!="-1"){
//            xiaoleiStr =xiaoleiStr+"where p.id = "+com_id
//        }
        def com_id = params.bigId
        println com_id
        def BrandArray = Brand.findAllByPurCategory(PurCategory.get(com_id))
        //def PurCategoryArray = PurCategory.findAllByPurBigCate(PurBigCate.get(com_id))
       // println BrandArray.size()

        render BrandArray as JSON
    }