通过ajax填充品牌名称下拉的模型下拉列表

Question

像这样看：

<div class="row">
    <div class="col-sm-6">
        <div class="form-group">
            <label for="inputEmail3" class="col-sm-4 control-label">Brand Name</label>
            <div class="col-sm-8">
                <select class="form-control" id="brand_mod" name="brand_name" required>
                    <option value="" selected disabled="disabled">Select Brand Here</option>
                    <?php foreach($b->result() as $row) { ?>
                    <option value="<?php echo $row->id; ?>"> <?php echo $row->brand_name; ?></option>
                    <?php } ?>
                </select>
            </div>
        </div>
    </div>  
    <div class="col-sm-6">
        <div class="form-group">
            <label for="inputPassword3" class="col-sm-4 control-label">Model</label>
            <div class="col-sm-8">
                <select name="model_number" class="form-control" id="models">
                    <option value="">--Select model --</option>
                </select>
            </div>
        </div>
    </div>  
</div>

在品牌名称下拉品牌名称下面是正确可见的，有我的型号名称下拉列表...我想当我点击任何品牌名称时，其模型会在模型下拉列表中显示 然后我的ajax电话是

<script>
    $('#brand_mod').change(function(){  

    var bbb = $('#brand_mod').val();
    //alert(bbb);

     $.ajax({
            type: "GET",
            url: '@Url.Action("<?php echo base_url(); ?>User/get_models", "Application")',
            contentType: "application/json; charset=utf-8",
            data: { brand_id : $('#brand_mod').val() },

            dataType: "json",
            cache: false,
            success: function(data) 
            { 
                alert(data);
                alert('Success'); 
                return false;
            },
            error:function()
            {
                alert('error');
                return false;
            }

        });
    });


</script> 

然后我的控制器就像这样进行ajax调用

public function get_models(){


    $id = $this->input->post('brand_id');
    $this->load->model("user/User_model");
    $result1 = $this->User_model->all_models($id);
    //$data = array();
     '<option value=""></option>'
    foreach($result1 as $row)
    {
     '<option value="'.$row->id'">'.$row->model_name'</option>'
    }
}

我的模特是

public function all_models($id)
{
    $this->db->where('brand_id',$id);
    $query = $this->db->get('wc_models');
    return $query->result_array();
}

但是我收到错误警告......代码有问题......我已经尽力了......请帮忙......