Question

I’m trying to get my head around a polymorphism/inheritance situation in C#.

What I have right now is these classes:

Lease (the base class containing the general data)
PrivateLease (inheriting from the Lease class)
BusinessLease (inheriting from the Lease class)

What I want to achieve is this:

Lease lease = new PrivateLease();

This works at the moment, but I am not able to access the properties on the PrivateLease object when doing this. At least not without casting the Lease object to a PrivateLease object first.

I’d like the Lease object to be the general object of either a PrivateLease or BusinessLease object which holds all the data for one of the objects. Then when inserting/updating/deleting to the database I’m going to ask which type it is first to dertermine which tables to insert the data into.

I’ve got a strange feeling that the above is not the right approach to solve this problem. Does anyone have any hints on this? 🙂 I’ve searched on google and read in my programming books and everyone suggests this approach of having a base class and then inherit from it to the other classes.

Any help/hint is greatly appreciated!

Thanks in advance.

EDIT

Should’ve elaborated a bit on this from the beginning, I’m sorry for that!

The above mentioned classes are merely just holding data from the UI of my ASP.NET solution to perform CRUD operations against the database via a Data Access Layer. So bascially these classes only contains a bunch of properties to hold data. I.e:

public class Lease
{
    public int Id { get; set; }
    public bool IsActive { get; set; }
    public string TypeOfRental { get; set; }
    public string RentalPeriod { get; set; }
    public DateTime TakeoverDate { get; set; }        
}

public class PrivateLease : Lease
{
    public string Floor { get; set; }
    public string Side { get; set; }
    public int FloorSize { get; set; }
    public int NumberOfRooms { get; set; }
}

etc..

The PrivateLease and BusinessLease classes are different because of the different leaseing-variables that exists in the real world 🙂

Basically I could just go with the two separate PrivateLease and BusinessLease objects, but since the model dictates that an Address object can hold one or more Leases, this is not an option.

To me it seems like I’m going to go through a major casting hell both on the ASP.NET frontend and on the DAL? :-/

Answer 1

Don’t decide (choose a logic) on the layer of consumer, but let to decide by the classes themselves:

// or you ILease interface if a parent class will not contain any shared logic
abstract class Lease
{
    public abstract void Do();

    // example of shared logic
    protected void Save(Lease l) { }
}

class PrivateLease : Lease
{
    public override void Do() { // private logic here }
}

class BusinessLease : Lease
{
    public override void Do() { // business logic here }
}

Usage:

Lease l = ...
l.Do(); // execute the logic

---

You may want to create a factory for objects creation:

static class LeaseFactory<T> where T : Lease, new() // constraint to require default constructor existence
{
    public static Leas Create()
    {
        return new T();
    }
}