Post sharp using instance member

Question

I am attempting to create an aspect to manage security on a few properties of a class. However, the security aspect for one member relies on the data in another property of the class. I've read some tutorials on the IntroduceAspect, but I'm not sure it's what I need.

public class ClassWithThingsIWantToSecure
{

    [SecurityAspectHere(inherits from LocationInterceptionAspect)]
    public int ThingIWantToSecure;

    public string ThingINeedToKnowAboutInSecurityAspect;
}

Can someone point me in the right direction for making the runtime value of ThingINeedToKnowAboutInSecurityAspect available in the SecurityAspect?

Answer 1

I have done something a bit like this before, I've knocked up a test on a machine with postsharp installed and just tried it out, here is the code...

    class Program
{
    static void Main(string[] args)
    {
        Baldrick baldrick = new Baldrick();
        baldrick.ThingINeedToKnowAboutInSecurityAspect = "Bob";
        Console.WriteLine("There are {0} beans", baldrick.ThingIWantToSecure);

        baldrick.ThingINeedToKnowAboutInSecurityAspect = "Kate";

        try
        {
            //This should fail
            Console.WriteLine("There are {0} beans", baldrick.ThingIWantToSecure);
        }
        catch (Exception ex)
        {
            //Expect the message from my invalid operation exception to be written out (Use your own exception if you prefer)
            Console.WriteLine(ex.Message);
        }
        Console.ReadLine();
    }


}

[Serializable]
public class SecurityAspect : LocationInterceptionAspect
{
    public override void OnGetValue(LocationInterceptionArgs args)
    {
        ISecurityProvider securityProvider = args.Instance as ISecurityProvider;
        if (securityProvider != null && securityProvider.ThingINeedToKnowAboutInSecurityAspect != "Bob")
            throw new InvalidOperationException("Access denied (or a better message would be nice!)");
        base.OnGetValue(args);
    }
}



public interface ISecurityProvider
{
    string ThingINeedToKnowAboutInSecurityAspect { get; }
}

public class Baldrick : ISecurityProvider
{
    public string ThingINeedToKnowAboutInSecurityAspect { get; set; }

    [SecurityAspect]
    public int ThingIWantToSecure{get { return 3; }}
}

So, the idea here is to interrogate the args.Instance property for the instace of the object that is being decorated.