我有數據庫表“事件”和“類別”。我想使用表單中的選擇下拉菜單為事件分配類別。我還希望能夠對其進行編輯和更新。我目前給了我以下錯誤的代碼 -SQLSTATE [23000]：違反完整性約束：1048 列 'category_id' 不能為空addEvent.blade.php  <div class="form-group">    <div class="form-group">      <div class="form-group">        {!! Form::Label('category_id', 'Category:') !!}        <select> class="form-control" name="category_id">          @foreach($categories as $category)            <option value='{{ $category->id}}'> {{ $category->category}}</option>          @endforeach         </select>      </div>    </div>  </div>事件控制器public function addEvent(Request $request){  $this->validate($request, [    'event_name'  => 'required',    'start_date'  => 'required',    'end_date'    => 'required',    'time'        => 'required',    'trip_id'     => 'required',  ]);    $start_date = Carbon::parse($request['start_date'])->format('Y-m-d');    $end_date = Carbon::parse($request['end_date'])->format('Y-m-d');    $tripCheck = Trip::where('id', $request['trip_id'])    ->whereDate('startdate', '<=', $start_date)    ->whereDate('enddate', '>=', $start_date)    ->whereDate('startdate', '<=', $end_date)    ->whereDate('enddate', '>=', $end_date)    ->first();    if ($tripCheck) {      $events = new Events;      $trips = Trip::all();      $categories = Categories::pluck('category','id');      $events->category_id = $request['category_id'];      $events->colour =  $request['colour'];      $events->event_name = $request['event_name'];      $events->start_date = $request['start_date'];      $events->end_date = $request['end_date'];      $events->time = $request['time'];      $events->address = $request['address'];      $events->notes = $request['notes'];      $events->trip_id = $request['trip_id'];      $events->save();return redirect('trips')->with('success', 'The new event has been added to your trip')->with('trips', $trips)->withCategories($categories);} else  {  return redirect('trips')->withErrors(['The dates you added are not within Trip start and end date.']);   }