语法：:p arameterize（） 必须是数组类型

我收到此错误

传递给 Illuminate\Database\Grammar：:p arameterize（） 的参数 1 必须是数组的类型，给定的字符串，

当我尝试使用选择表单添加我的视图时。但是当我删除它时，我没有得到任何错误。我只是尝试在选择列表中输入多个值。我需要用于此目的吗？array[]foreach

视图

<div class = "form-group {{ $errors->has('approver') ? ' has-error' : '' }}">

    <label for = "approver" class = "control-label">Approver:</label>

    <select name = "approver[]" multiple class = "form-control select2-multi">

        @foreach ($approver as $list)
            <option value = "{{ $list->id }}">{{ $list->username }}</option>
        @endforeach

    </select>

    @if ($errors->has('approver'))
        <span class = "help-block">{{ $errors->first('approver') }}</span>
    @endif

</div>

控制器

public function getDocuments()
{
   $approver = DB::table('users')->where('id', '!=', Auth::id())->get();

   return view ('document.create')->with('approver', $approver);
}

public function postDocuments(Request $request)
{

    $this->validate($request,
    [
        'title' => 'required|regex:/(^[A-Za-z0-9 ]+$)+/|max:255',
        'content' => 'required',
        'category' => 'required',
        'recipient' => 'required',
        'approver' => 'required',
    ]);     


    $document = new Document();
    $approve = new Approve();
    $user = Auth::user();
                                //Request in the form
    $document->title = $request->title;
    $document->content = $request->content;
    $document->category_id = $request->category;
    $approve->approver_id = $request->approver;

    $approve->save();

    $document->save();

    $document->sentToApprovers()->sync([$approve->id],false);

}

更新

我死了并转储变量并给出了一个值数组。$approver

此外，die并转储，正如您在此处看到的，我在选择列表中输入了4和5的id。$request