Laravel 5.1 - Crud with ajax

Hi i'm doing a CRUD with ajax, i have a problem with store comment submited. I have this error:

QueryException in Connection.php line 655: SQLSTATE[23000]: Integrity constraint violation: 1048 Column 'user_id' cannot be null (SQL: insert into comments (content, user_id, product_id, article_id, updated_at, created_at) values (my comment, , , , 2016-06-20 10:37:57, 2016-06-20 10:37:57))

i tryed to store a comment with text "my comment". My input "content" pass to my controller but my input hidden like "article_id", "user_id", "product_id" are not passing to my controller.

CommentController:

public function store(Request $request)
    {

        if($request->ajax()){
            $comment = new Comment();
            $comment->content = $request->input('content'); 
            $comment->user_id = $request->input('user_id'); 
            $comment->product_id = $request->input('product_id');
            $comment->article_id = $request->input('article_id');  

            $comment->save(); 


            return response()->json([

                "message" => "Comment pubblished!"
            ]);
        }
}

Form Comment article:

{!! Form::open(['route'=>'comment.store'] )!!}   



                                <div class="form-group">
                                    <label for="reply-text" class="sr-only">Commenta</label>


                                    {!! Form::textarea('content', null, ['id'=>'content','class'=>'form-control','rows'=>'3', 'placeholder'=>'Commenta','required'])!!}


                                </div>
                                <input type="hidden" id="token" name="_token" value="">
                                {!! Form::hidden('user_id', Auth::user()->id, null,['id'=>'user_id','class' =>'form-control'])!!}

                                {!! Form::hidden('article_id', $article->id, null,['id'=>'article_id','class' =>'form-control'])!!}

                                {!! Form::hidden('article_slug', $article->slug, null,['id'=>'article_slug','class' =>'form-control'])!!}

                                {!!link_to('#', $title='Comment post', $attributes =['id'=>'commento', 'class'=>'btn btn-lg btn-dark btn-outline'], $secure = null)!!} 

{!! Form::close()!!}

comment.js :

$("#commento").click(function(){

    var dato= $("#content").val();
    var dato2= $("#user_id").val();
    var dato3= $("#article_id").val();
    var dato4= $("#product_id").val();
    var route = "http://localhost:8000/comment";
    var token = $("#token").val();

    $.ajax({
        url: route,
        headers:{'X-CSRF-TOKEN':token},
        type: 'POST',
        dataType: 'json',
        data:{
            content: dato, 
            user_id: dato2, 
            article_id: dato3, 
            product_id: dato4
        },


    });

});

via Chebli Mohamed