public async Task <IActionResult> Borrow(int id) { var copy = _context.Copies.FirstOrDefault(c => c.Book.Id == id && c.IsAvailable); if (copy != null) { var borrowing = new Borrowing { Copy = copy, DateOfBorrowing = DateTime.Today, ApplicationUser = await _userManager.GetUserAsync(User) }; await _context.Borrowings.AddAsync(borrowing); copy.IsAvailable = false; await _context.SaveChangesAsync(); } return(RedirectToAction(nameof(Index))); }