public async Task <IHttpActionResult> AddDemand(Demand demand)
        {
            try
            {
                _DemandRepository = new DemandRepository();
                await _DemandRepository.AddDemand(demand);

                return(Ok());
            }
            catch (Exception e)
            {
                return(BadRequest("Error: " + e.Message));
            }
        }
        public async Task <IHttpActionResult> GetBookById(string id)
        {
            try
            {
                _BookRepository   = new BookRepository();
                _DemandRepository = new DemandRepository();
                Book book = await _BookRepository.GetBookById(id);

                User user = await this.AppUserManager.FindByNameAsync(User.Identity.Name);

                if (await _DemandRepository.CheckDemandExist(user, book) == null)
                {
                    await _DemandRepository.AddDemand(new Demand()
                    {
                        Book = book, User = user
                    });
                }
                return(Ok(book));
            }
            catch (Exception e)
            {
                return(BadRequest("Error: " + e.Message));
            }
        }