public IEnumerable <CommentViewModel> Comment(CommentPostViewModel model)
 {
     if (ModelState.IsValid)
     {
         _service.AddComment(model, GetClientIp());
         return(_service.RetrieveCommentList(model.ArticleID));
     }
     throw new HttpResponseException(Request.CreateErrorResponse(HttpStatusCode.BadRequest, ModelState));
 }