public string GetOrderHistoryByCustomer(int id) { // This method is called because we need the information on the whole catalog // Since the catalog is small I went with this implementation. // If it was much large I would only fill the library with the relevant books FillBookLibrary(); // Attempt to find the customer CustomerEntity dbCustomer = _context.Customers .Include(o => o.Orders) .ThenInclude(ol => ol.Orderlines) .FirstOrDefault(c => c.Id == id); // If the customer was not found then let the user know if (dbCustomer == null) { return("No Customer exists by this name."); } string result = ""; // if one was found then map it to a usable object Library.Models.Customer m_customer = Mapper_Customer.MapCustomerWithOrders(dbCustomer); // Build the string that needs to be returned result += m_customer; foreach (Library.Models.Order order in m_customer.Orders) { result += $"\n{order}"; } return(result); }