public IHttpActionResult Update(int id, CommentOutputData comment)
        {
            if (!ModelState.IsValid)
            {
                return BadRequest(ModelState);
            }

            var existingComment = this.data.Comments.All().FirstOrDefault(u => u.Id == id);
            if (existingComment == null)
            {
                return BadRequest("Such comment does not exists!");
            }

            existingComment.Content = comment.Content ?? existingComment.Content;

            this.data.Comments.Update(existingComment);
            this.data.SaveChanges();

            return Ok();
        }
        public IHttpActionResult Create(int id, CommentOutputData comment)
        {
            if (!ModelState.IsValid)
            {
                return BadRequest(ModelState);
            }

            var existingUser = this.data.Users.All().FirstOrDefault(u => u.Id == id);
            if (existingUser == null)
            {
                return BadRequest("Such user does not exists!");
            }

            var newComment = new Comment
            {
                Content = comment.Content,
            };

            existingUser.Comments.Add(newComment);
            this.data.SaveChanges();

            return Ok(newComment.Id);
        }