Get method name using Lambda expression

Question

I am trying to get the method name for a type using a lambda expression. I am using Windows Identity Foundation and must define access policies with a type name with a namespace as a resource and a method name as an action. Here is an example.

This is the type from which I get the type name and method name:

namespace My.OrderEntry { public class Order { public void AddItem(string itemNumber, int quantity) {} } } 

Here is how I would like to define an access policy through DSL:

 ForResource<Order>().Performing(o => o.AddItem).AllowUsersHaving(new Claim()); 

From this statement, I would like to get "My.OrderEntry.Order" as a resource and "AddItem" as an action. Getting a type name with a namespace is not a problem, but I don't think I can use lambda for the method I'm trying to do.

 public static IPermissionExp Performing<T>( this IActionExp<T> exp, Func<T, delegate???> action) {} //this is where I don't know what to define 

Can this be done? Is there any other way to do such things without using magic strings?

Answer 1

There are two ways to do this:

1: you can do overloads that accept various Func and Action delegates (e.g. Expression<Func<T, Func<TParam1,TParam2, TReturn>> ). Please note that your callers must explicitly specify common parameters either in a method call or by creating a delegate. This will be used as follows:

 ForResource<Order>().Performing(o => new Action<string>(o.AddItem)).AllowUsersHaving(new Claim()); 

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2: You can take an Expression<Action> , which contains a method call, and parse a MethodInfo that is called from the expression tree. This will be used as follows:

 ForResource<Order>().Performing(o => { o.AddItem(null); }).AllowUsersHaving(new Claim()); 

Answer 2

This seems to be what you are looking for if you want the name of the action delegation method to be passed to the Run function.

 public static IPermissionExp Performing<T>( this IActionExp<T> exp, Expression<Action<T, string, int>> action) { var expression = action.Body as MethodCallExpression; string actionMethodName = string.Empty; if (expression != null) { actionMethodName = expression.Method.Name; } // use actionMethodName ("AddItem" in the case below) here } 

This will allow you to call a method like this ...

 ForResource<Order>().Performing((o, a, b) => o.AddItem(a, b)).AllowUsersHaving(new Claim()); 

Answer 3

I recently did something at work where you defined a method using lambda, which then got an internal object. You can also use strings or pass to MethodInfo, but the first one is not type safe (and typos are a big risk), and the latter is not very elegant.

Basically, I had such a method (this is not an exact method, it is a bit more advanced):

 public void SetRequest(Request req, Expression<Func<Service, Func<long, IEnumerable<Stuff>>> methodSelector); 

The key here is the “Expression” thing, this allows you to “choose” a method similar to this:

 SetRequest(req, service => service.SomeMethodTakingLongReturningStuffs); 

The method selector turns into an expression tree from which you can extract different bits of data. I don’t remember exactly what the resulting tree looks like, it also depends on how your lambdas look.

Answer 4

Instead, you can pass it as an action that does not call any return type. This is still a bit dirty, because you need to pass some arguments to the method to compile it.