如何根据PHP中的另一个DropDown填充DropDown

Question

我在下面创建了这段代码，根据第一个下拉列表（部门）填写第二个下拉列表用户这是我的Ajax请求

<script type="text/javascript">
    $(document).ready(function(){

        $("#sel_depart").on('change', function(){
            var deptid = $(this).val();

            $.ajax({
                url: 'action.php',
                type: 'post',
                data: {depart:deptid},
                dataType: 'json',
                success:function(response){

                    var len = response.length;

                    $("#sel_user").empty();
                    for( var i = 0; i<len; i++){
                        var id = response[i]['id'];
                        var name = response[i]['name'];

                        $("#sel_user").append("<option value='"+id+"'>"+name+"</option>");

                    }
                }
            });
        });

    });
</script>

这是第一次下拉

<tr>
                <td>departments/td>
                <td>

                <select id="sel_depart" ><?php foreach($myrow2 as $row){?>
                <option value="<?php echo $row['id'] ?>"> <?php echo $row['ename']?></option> <?php }?>
                 <div class="clear"></div>
                </select>
                </td>

            </tr>

这是第二个

<tr> 
                <td>users</td>
                <td>
    <select id="sel_user">
        <option value="0">- Select A user-</option>
    </select> 
</td>
</tr>

Ajax向action.php发送包含以下内容的请求：

if (isset($_POST['depart'])){
$departid = $_POST['depart'];   // department id
if($obj->spinner2($departid)){
    header("location:merchant.php?msg=district fetched ");
}
}

这是函数spinner2：

public function spinner2($departid){
    $sql="SELECT id,ename FROM district where city_id =".$departid ;
    $arr = array();
    $result = mysqli_query($this->con,$sql);
    while ($row = mysqli_fetch_array($query)){
        $userid = $row['id'];
        $name = $row['ename'];
        $arr[] = array("id" => $userid, "name" => $name);
    }
     $users_arr=json_encode($arr);
    echo $users_arr;
    return $users_arr;
}

当我选择一个部门时没有任何事情发生