public void Test()
        {
            var authors = new List<Author>
            {
                new Author
                {
                    BirthDate = DateTime.Now,
                    FirstName = "First Name"
                },
                new Author
                {
                    BirthDate = DateTime.Now,
                    FirstName = "First Name 2"
                },
            };

            var books = new List<Book>();
            authors.ForEach(x =>
            {
                var book = new Book
                {
                    Description = "Description " + x.AuthorId,
                    AuthorId = x.AuthorId
                };

                //db.Authors.Attach(x);
                //db.Entry(x).State = EntityState.Added;

                x.Books.Add(book);
            });

            db.Authors.AddRange(authors);
            db.SaveChanges();

            var id = authors.FirstOrDefault().AuthorId;
        }
        public IHttpActionResult PostBook(Models.BooksModel.BooksModel booksModel)
        {
            if (!ModelState.IsValid)
                return BadRequest(ModelState);

            var book = new Book
            {
                Description = booksModel.Description,
                Title = booksModel.Title,
                PublishDate = booksModel.PublishDate
            };
            try
            {
                db.Books.Add(book);
                db.SaveChanges();

                return Created("DefaultApi", new { id = book.BookId });
            }
            catch (Exception)
            {
                return StatusCode(HttpStatusCode.InternalServerError);
            }
        }