c# - How to copy or get a changing value of a model property to another model?

Question

I am creating a web app using C# MVC. I created a model named Trip.cs with properties as below:

public int ID {get; set;}
public string Destination {get; set;}
public DateTime DepartureDate {get; set;}
public string MeetPlace {get; set;}
public int NumberOfSeats {get; set;}
public virtual ApplicationUser User { get; set; }
public string UserId { get; set; }

I created another model called ReservedTrip.cs identical with Trip.cs with the same properties. What I do is when the logged user clicks on the Actionlink named "Reserve Trip", I save this "Trip" to the ReservedTrip.cs and I decrease the number of property NumberOfSeats with 1. So in other words I copy this "Trip" data from Trip.cs to ReservedTrip.cs. The problem is when I display in a view the data from model Trip.cs the number of NumberOfSeats changes, but in the model ReservedTrip.cs the property NumberOfSeats doesn't change. So I want the changes of property NumberOfSeats of model Trip.cs to change in the property NumberOfSeats to be changed with the same value.

Can anyone help me?

Answer 1

From a design standpoint, it is better to not have a copy of any table. A good design for this situation can be something like this.

public class Trip
{
    public int ID {get; set;}
    public string Destination {get; set;}
    public DateTime DepartureDate {get; set;}
    public string MeetPlace {get; set;}
    public int NumberOfSeats {get; set;}
    public int CreatedByUserID {get; set;}

    public virtual ApplicationUser CreatedByUser {get; set;}
    public virtual ICollection<TripReservation> Reservations {get;set;}
}
public class TripReservation
{
    public int ID {get; set;}
    public int TripID {get; set;}
    public int UserID {get; set;}

    public virtual Trip Trip {get; set;}    
    public virtual ApplicationUser User {get; set;}
}

then in your controller you can construct a view model with the number of seats available being

numberOfSeatsAvailable = trip.NumberOfSeats - trip.Reservations.Count();

If a reservation can reserve more than 1 seat, you can sum that from all reservations for that trip.

Example: ViewModel

public class TripReservationsViewModel
{
    public Trip Trip { get; set; }
    public int NumberOfSeatsAvailable { get; set; }
}

Example: Controller

public ActionResult TripDetails(int id)
{
    var trip = db.Trips.FirstOrDefault(trip => trip.ID == id);
    if (trip == null)
    {
        // Trip does not exist, 
        // Redirect the user to the trips home page
        //
        return RedirectToAction("Index");
    }

    var viewModel = new TripReservationsViewModel();

    viewModel.Trip = trip;
    viewModel.NumberOfSeatsAvailable = trip.NumberOfSeats - trip.Reservations.Count();

    return View(viewModel);
}

Example: View

@model TripReservationsViewModel

<h1>Trip Details</h1>
<p>Seats available: @Model.NumberOfSeatsAvailable</p>
etc...