Data type to handle decrypting data - as method param data type

Question

On several of our AJAX endpoints, we accept a string and immediately in the method, we try to decrypt the string into an int. Seems like a lot of repetitive code.

public void DoSomething(string myId)
{
  int? id = DecryptId(myId);
}

Where DecryptId is a common method (in the base controller class)

I would like to create a class that does all this for me and use this new class as the data type in the method argument (instead of string) and then a getter that returns the decrypted int?

What's the best way to do this?

Answer 1

Here's my implementation that is working.

public class EncryptedInt
{
    public int? Id { get; set; }

    // User-defined conversion from EncryptedInt to int
    public static implicit operator int(EncryptedInt d)
    {
        return d.Id;
    }
}

public class EncryptedIntModelBinder : IModelBinder
{
    public object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
    {
        if (bindingContext == null)
        {
            throw new ArgumentNullException("bindingContext");
        }

        var rawVal = bindingContext.ValueProvider.GetValue(bindingContext.ModelName);
        var ei = new EncryptedInt
        {
            Id = Crypto.DecryptToInt(rawVal.AttemptedValue)
        };
        return ei;
    }
}

public class EncryptedIntAttribute : CustomModelBinderAttribute
{
    private readonly IModelBinder _binder;

    public EncryptedIntAttribute()
    {
        _binder = new EncryptedIntModelBinder();
    }

    public override IModelBinder GetBinder() { return _binder; }
}

... and in Global.asax.cs in the Application_Start method (in case you want it global for all EncryptedInt types instead of using Attribute on each reference) ...

// register Model Binder for EncryptedInt type
ModelBinders.Binders.Add(typeof(EncryptedInt), new EncryptedIntModelBinder());