ThinkPHP 3단계 연계

<div id="cBox">
<select id="pro">
<option>--请选择省份--</option>
</select>
</div>

$(function(){
$.ajax({type:'GET', url:'__URL__/linkage', data:'upid=0',
success:function( data ){
var proOption = '';//用来存放省份的选项
for( var i=0;i<data.length;i++){
proOption += &#39;<option value=&#39;+data[i].id+&#39;>&#39;+data[i].name+&#39;</option>&#39;;
}
$(&#39;#pro&#39;).append(proOption);
}, dataType:&#39;json&#39;
});
$(&#39;#cBox&#39;).on(&#39;change&#39;,&#39;select&#39;,function(){
var ob = $(this);
ob.nextAll(&#39;select&#39;).remove();
var val = $(this).val();
$.get(&#39;__URL__/linkage&#39;, {upid:val}, function(res){
if( res.length <=0 ) return false;
var len = $(&#39;#cBox select&#39;).length;

switch( len ){
case 1:
idValue = &#39;city&#39;;
break;
case 2:
idValue = &#39;qu&#39;;
break;
case 3:
idValue = &#39;xian&#39;;
break;
case 4:
idValue =&#39;dao&#39;;
break;
default:
idValue = &#39;222&#39;;
break;
}
var select = &#39;<select id="&#39;+idValue+&#39;"><option>--请选择--</option>&#39;;
for( var i=0;i<res.length;i++){
select += &#39;<option value="&#39;+res[i].id+&#39;">&#39;+res[i].name+&#39;</option>&#39;;
}
select +=&#39;</select>&#39;;
ob.after( select );
},&#39;json&#39;
);
});
});

public function linkage() {
$map['pid'] = I('get.upid');
$cityList = M('category')->where($map)->select();
echo json_encode($cityList);
}