public IHttpActionResult Create(AuthorModel author)
        {
            if (!this.ModelState.IsValid)
            {
                return BadRequest(ModelState);
            }

            var newAuthor = new Author
            {
                FirstName = author.FirstName,
                LastName = author.LastName
            };

            this.data.Authors.Add(newAuthor);
            this.data.SaveChanges();

            author.AuthorId = newAuthor.AuthorId;
            return Ok(author);
        }
        public IHttpActionResult Update(int id, AuthorModel author)
        {
            if (!this.ModelState.IsValid)
            {
                return BadRequest(ModelState);
            }

            var authorFromDb = this.data.Authors.All().FirstOrDefault(s => s.AuthorId == id);
            if (authorFromDb == null)
            {
                return BadRequest("Such student does not exist!");
            }

            authorFromDb.FirstName = author.FirstName;
            authorFromDb.LastName = author.LastName;
            this.data.SaveChanges();

            author.AuthorId = id;
            return Ok(author);
        }