三级联动

 <div class="form-group">
     <label class="">大分类：</label>
     <select name="max" class="form-control" style=" 200px"   id="max"  >
         <option value="" >--请选择大分类--</option>
         <volist name="maxtype" id='vvo'  >
         <option value="<?php echo $vvo['id'];?>" <?php if($max==$vvo['id']){ echo selected;} ?> ><?php echo $vvo['name'];?></option>
        </volist>
     </select>

     <label class="">小分类：</label>
     <select name="two" class="form-control" style=" 200px"  id="two">
         <option value="" >--请选择小分类--</option>
         <?php if(!empty($s_class)){ foreach($s_class as $k=>$v){?>
            <option value="<?php echo $v['id'];?>" <?php if($two==$v['id']){ echo selected;} ?> ><?php echo $v['name'];?></option>
         <?php } } ?>

     </select>

     <label class="">品牌：</label>
     <select name="brand_id" class="form-control" style=" 200px" id="pinpai">
         <option value="" >--请选择品牌--</option>
         <?php if(!empty($brand_data)){   foreach($brand_data as $k=>$v){?>
         <option value="<?php echo $v['brand_id'];?>" <?php if($brand_id === $v['brand_id']){ echo selected;} ?>><?php echo $v['brand_name']; ?></option>
         <?php } } ?>
     </select>

</div>

《script》

  $(document).on('change','#max',function() {
       var maxid = $("select[name=max]").val();
       $(".dtype").val(maxid);

       $.ajax({
           url:"/admin/product/secondlevel",
           type:"post",
           data:{
               id:maxid
           },
           success: function (data) {
                console.log(data)
            str='<option value="">--请选择--</option>';
            $.each(data,function (k,v) {
                str+='<option class="rep"         id="' + v.id + '"   value="'+v.id+'">'+v.name+'</option>';
                
            })
               $("#two").append($('#two').html(str));
       }
       })
   });

$(document).on('change',"#two",function () {
       id= $(this).val()
       $(".mtype").val(id);

    $.ajax({
        url:"/admin/product/threelist",
        type:"post",
        data:{
            id:id
        },
        success: function (data) {
            console.log(data)
            str='<option value="">--请选择--</option>';
            $.each(data,function (k,v) {
                str+='<option class="rep"         id="' + v.brand_id + '"   value="'+v.brand_id+'">'+v.brand_name+'</option>';

            })
            $("#pinpai").append($('#pinpai').html(str));

        }
    })
})

public  function  threelist(){
    $id=$_POST['id'];
    $classification_derive_brand=M('classification_derive_brand')->group('brand_id')->where("c_sid=$id")->select();
    $this->ajaxReturn($classification_derive_brand);
}