fastadmin选择下拉框两级联动

<div class="form-group">
        <label class="control-label col-xs-12 col-sm-2">发送者:</label>
        <div class="col-xs-12 col-sm-8">
            {:build_select('row[sender]', $senders, null, ['class'=>'form-control selectpicker sender', 'data-rule'=>'required'])}
        </div>
    </div>
    <div class="form-group">
        <label class="control-label col-xs-12 col-sm-2">{:__('External_userid')}:</label>
        <div class="col-xs-12 col-sm-8">
            <select  id="c-external_userid" class="form-control selectpicker" name="row[external_userid]">
                <option value="0" id="external_userid">请选择</option>
            </select>
        </div>
    </div>

1.build_select是框架内置的函数，$senders为数据集

$('.sender').on('changed.bs.select', function() {//单击时方法
        // console.log('agja');
        var ids = $(this).val();
        console.log($('.sender').selectpicker('val'));

        $.post('qywx.gmsglog/getFollowUser',
            {
                'userid':ids
            },
            function (data) {
                $('#c-external_userid').html("");
                for(var i in data){
                    $('#c-external_userid').append('<option value="'+data[i]+'">'+data[i]+'</option>')
                }
                $('select').selectpicker('refresh');
            }
        );
    });

1.当第一个select点击选择时候，通过jq监听拿到数据，传送给后台接口

public function getFollowUser()
    {
        $userid           = $this->request->post('userid');
        $external_userids = Db::name('qywx_resident_follow_user')->field('external_userid')->where('userid', $userid)->select()->toArray();
        $external_userids = array_column($external_userids, 'external_userid');
        $external_userids = array_combine($external_userids, $external_userids);

        return json($external_userids);

    }

1.通过json返回数据

思考：

　　1.定义两个下拉选择框，通过事件进行关联，拿到第一个下拉框的id传送给后台，拿到数据

　　2.每次点击的时候需要清空之前的option

　　3.$('select').selectpicker('refresh');刷新一下select，重新加载append数据

　　4.select加multiple=""属性为多选