Passing a custom attribute with a variable value as a parameter

Question

I created a custom attribute class that will check the system security and throws an authentication exception if there is a security error.

public class EntityChecker: System.Attribute
{
    public EntityChecker(int entityId)
    {
        // doing some logic to check if the entityId is allowed to be inserted
    }
}

I want to use this custom attribute as a declaration to an entity addition function and I want to pass a variable from the function to the attribute constructor. can something like this be done?

[EntityChecker(entityId)]
public int AddNewEntity(entityId)
{
 // logic of entity addition
}

Answer 1

Can something like this be done ?!

No. Constructor parameters in attributes must be resolved at compile time. They are intended as metadata on the type or method itself, not something that would be used per call or per instance.

Given your description, an attribute is likely not an appropriate way to handle this. Since you want to run extra code that happens per call, you will need a different technique. For example, you could pass a delegate, ie:

public int CheckedAddEntity(int entityId, Func<int, int> funcToAdd)
{
    // Perform your checking on entityId here
    return funcToAdd();
}

This would let you then call via something like:

int result = CheckedAddEntity(entityId, AddNewEntity);

Answer 2

In this case, I recommend looking at Aspect-Oriented programming. It is a different way of doing code, but one that allows you to re-use the boilerplate logic (e.g. authentication) throughout. You might have to design your attribute a little bit differently, but all of the logic can be put into an "aspect" which then gets compiled automatically into the code when you build the project.

I personally use PostSharp, although I know there are others out there. They have a free license available for development; as long as you don't require advanced functionality, it's very cost-effective.

http://www.postsharp.net/blog/post/5-Ways-That-Postsharp-Can-SOLIDify-Your-Code-Authorization