使用laravel选择类别后选择子类别

I am creating a form in which I get subcategories after I select one category. But problem is that I have only one table in which categories and subcategories are stored.

All the values in the table have their auto-increment id and a parent_id. For all Main-Categories, parent_id is 0. and Sub-categories have Main-Categories id as their parent_id. As shown in image

Depending upon this condition I build a query and passed that query to my view through controller as

$k = DB::table('main_category')->where('parent_id','=','0')->lists('name','id');

And in view:

<div class="form-group">
    {!! Form::label('category','Category:') !!}
    <select name="category" id="category" class="form-control input-sm">
        @foreach($k as $a)
        <option value="{{$a}}">{{$a}}</option>
            @endforeach
    </select>
</div>

<div class="form-group">
    {!! Form::label('subcategory','Subcategory:') !!}
    <select name="subcategory" id="subcategory" class="form-control input-sm">
            <option value=""></option>
    </select>
</div>

My script.js:

    $('#category').on(change,function(e){
  console.log(e);
   var cat_id = e.target.value;

    //ajax
    $get('/ajax-subcat?cat_id='+ cat_id,function(data){
        //success data
        //console.log(data);
        $('#subcategory').empty();
        $.each(data,function(index,subcatObj){
            $('#subcategory').append('<option value ="'+subcatObj.id+'">'+subcatObj.name+'</option>');
        });

    });
});

Routes.php:

    Route::resource('event', 'EventsController');

Route::get('/ajax-subcat',function () {
    $cat_id = Input::get('cat_id');
//    return $cat_id;
    $subcategories = DB::table('main_category')->where('name', '=',$cat_id)->get();
    return Response::json($subcategories);
});

But when I use $a->name or $a->id, I get error as trying to get non object property.

Also, I am taking refrence of this video

Here are some corrections taking reference from this page for script. In Controller:

 $s = Category::all()->where('parent_id','=','0');

View:

<div class="form-group">
    {!! Form::label('category','Category:') !!}
    <select name="category" id="category" class="form-control input-sm">
        @foreach($s as $k)
            <option value="{{ $k['id'] }}">{{ $k['name'] }}</option>
        @endforeach
        {{--<option value="Dance And Music">Dance And Music</option>--}}
    </select>
</div>

<div class="form-group">
    {!! Form::label('subcategory','Subcategory:') !!}
    <select name="subcategory" id="subcategory" class="form-control input-sm">
        <option value=""></option>
    </select>
</div>

Script:

        $(document).ready(function () { 
            $('#category').on('change',function(e){
            console.log(e);
            var cat_id = e.target.value;
            //console.log(cat_id);
            //ajax
            $.get('/ajax-subcat?cat_id='+ cat_id,function(data){
                //success data
               //console.log(data);
                var subcat =  $('#subcategory').empty();
                $.each(data,function(create,subcatObj){
                    var option = $('<option/>', {id:create, value:subcatObj});
                    subcat.append('<option value ="'+subcatObj+'">'+subcatObj+'</option>');
                });
            });
        });
    });

Routes.php

Route::get('/ajax-subcat',function () {
$cat_id = Input::get('cat_id');
$subcategories = DB::table('main_category')->where('parent_id','=',$cat_id)->lists('name');
return Response::json($subcategories);});

for this change the name with id

you set the id in the where field instead of name

   Route::resource('event', 'EventsController');

    Route::get('/ajax-subcat',function () {
     $cat_id = Input::get('cat_id');
       //          return $cat_id;
      $subcategories = DB::table('main_category')->where('id', '=',$cat_id)->get();
return Response::json($subcategories);
 });

As you need to find all Sub Category for a Main Category your query should be

Route::get('/ajax-subcat',function () {
    $cat_id = Input::get('cat_id');
//    return $cat_id;
    //All the catagory belong to parentid is cat_id (main catagoryId)
    $subcategories = DB::table('main_category')->where('parent_id', '=',$cat_id)->get();
    return Response::json($subcategories);
});