Question

Let me explain my question by posing a hypothetical situation. Lets start with a class:

public class PaymentDetails
{
    public int Id {get;set;}
    public string Status {get;set;}
}

And then I have another class:

public class PaymentHelper
{
    private PaymentDetails _paymentDetails;
    public PaymentDetails MyPaymentDetails{ get { return _paymentDetails; } }

    public PaymentHelper()
    {
        _paymentDetails = new PaymentDetails(); 
    }

    public void ModifyPaymentDetails(string someString)
    {
        // code to take the arguments and modify this._paymentDetails
    }
}

OK, so I have these two classes. PaymentHelper has made the property MyPaymentDetails read-only.

So I cannot instantiate PaymentHelper and modify MyPaymentDetails like this:

PaymentHelper ph = new PaymentHelper();
ph.MyPaymentDetails = new PaymentDetails(); // Not allowed!!! 

But I can modify the public properties inside of ph.MyPaymentDetails like this:

ph.MyPaymentDetails.Status = "Some status"; // This is allowed

How do I prevent that from working? Or is there no good way of doing that?

Answer 1

The idea of protecting the properties of a complex type that is itself a property isn’t available from a language construct at that level.

One option is to design the contained type in such a way as to make its properties read-only using the access modifiers (public set, protected set, private set, etc).

My preference is to expose it as an interface to public consumers:

public class PaymentHelper
{
    private PaymentDetails _paymentDetails;
    public IPaymentDetails MyPaymentDetails{ get { return _paymentDetails; } }

    public PaymentHelper()
    {
        _paymentDetails = new PaymentDetails(); 
    }

    public void ModifyPaymentDetails(string someString)
    {
        // code to take the arguments and modify this._paymentDetails
    }
}

interface IPaymentDetails
{
   int Status { get; }
}

Code inside the PaymentHelper class can then use the PaymentDetails class directly, and code outside the class won’t be able to use PaymentDetails unless they cast directly to it, which you can stop if you don’t release the PaymentDetails class and only provide the interface.

Of course, you can never really stop the determined person who may use reflection to set things. I tend to let these people break the code 🙂