如何在Laravel 5.6中的数据依赖选择输入中掌握表数据以编辑表单？

Question

与Laravel 5.6一起工作，我有表名称工具，并且在此表数据编辑表单中具有省，区和镇数据依赖选择输入，

<select name="provincename" id="provincename" class="form-control input dynamic" data-dependent="districtname" >
            <option value="{{$vehicles->provincename}}">{!! $vehicles->provincename !!}</option>
            @foreach($town_list as $town)

            <option value="{{$town->provincename}}">{{$town->provincename}}</option>
            @endforeach
        </select>

 <div class="form-group row required{{ $errors->has('districtname') ? ' has-error' : '' }}">
            <label for="exampleFormControlSelect1" class="col-form-label col-md-3 col-lg-2">District</label>
            <div class="col-md-8">
           <select name="districtname" id="districtname" class="form-control input dynamic" data-dependent="townname" >
            <option value="{{$vehicles->districtname}}">{!! $vehicles->districtname !!}</option>
</select> 

这种依赖性的控制器

 function fetch(Request $request)
    {
        $select = $request->get('select');
        $value = $request->get('value');
        $dependent = $request->get('dependent');
        $data = DB::table('towns')
               ->where($select,$value)
               ->groupBy($dependent)
               ->get();

               $output = '<option value="">Select '.ucfirst($dependent).'</option>';
               foreach ($data as $row) {
                $output .= '<option value="' .$row->$dependent. '">
                          '.$row->$dependent.'</option>';
               }
               echo $output;
    }

但是当我单击编辑表单时，省名值会在选择输入中正确选择。但未根据车辆表格值选择地区名称。我该如何解决这个问题？来自城镇表的地区数据