Method 1:
        public async Task<int?> GetQueuePositionAsync(User user, Book book)
        {
            var bookRservations = await context.Reservations
                .Where(r => r.BookID == book.ID)
                .OrderBy(r => r.CreatedOn).ToListAsync();
            var position = bookRservations.FindIndex(r => r.UserID == user.Id);
            return ++position;
        }

Method 2:
        public async Task<bool> IsUserFirstToCheckOutAsync(string userId, int bookId)
        {
            var isBookReservedByUser = await IsBookReservedByUserAsync(bookId, userId);
            if (isBookReservedByUser)
            {
                var reservations = await GetReservationsByBookIdAsync(bookId);
                var userFirstInQueue = reservations.OrderBy(x => x.CreatedOn).First();
                var isCurrentUserFirst = userFirstInQueue.UserID == userId;
                return isCurrentUserFirst;
            }
            else return false;
        }