How Func return Object name as string

Question

I have static method like this :

    public static string MyMethod(Func<Student, object> func)
    {            
        return ??? ;
    }

and I use it as following :

    var s1 = MyMethod(student => student.ID); // Return "ID" ???
    var s2 = MyMethod(student => student.Age); // Return "Age" ???
    var s3 = MyMethod(student => student.Name); // Return "Name" ???

How write method that return the following results ?

s1 : "ID"
s2 : "Age"
s3 : "Name"

* return each property`s name after => as string

You cannot with this signature -- it must be something such as `Expression>`. — Jon, Dec 12 '13 at 20:09

vittore · Accepted Answer · 2013-12-12T20:17:24.957

1

You can change signature of your method from

  public static string MyMethod(Func<Student, object> func)

change it to

  public static string MyMethod(Expression<Func<Student, object>> func) {
     return GetMemeberName(func)
  } 

  public static string GetMemberName(Expression expression)
    {            
        if (expression is LambdaExpression)
        {
            var lambdaExpression = (LambdaExpression)expression;
            return GetMemberName(lambdaExpression.Body);                              
        }

        if (expression is MemberExpression)
        {
            var memberExpression = (MemberExpression)expression;
            if (memberExpression.Expression.NodeType == ExpressionType.MemberAccess)
            {
                return GetMemberName(memberExpression.Expression)+ "."+ memberExpression.Member.Name;
            }
            return memberExpression.Member.Name;
        }

        if (expression is UnaryExpression)
        {
            var unaryExpression = (UnaryExpression)expression;
           if (unaryExpression.NodeType != ExpressionType.Convert)
                throw new Exception(string.Format(
                    "Cannot interpret member from {0}",
                    expression));
            return GetMemberName(unaryExpression.Operand);
        }
        throw new Exception(string.Format("Could not determine member from {0}",expression));
    }

edited Dec 12 '13 at 20:17

answered Dec 12 '13 at 20:07

vittore

17,449
6
44
82

2

This is good, but you have to tell him how to make it work. The OP has `Func<>`, not `Expression`. – Gabe Dec 12 '13 at 20:10
4

Basically this is a bunch of code that, while useful, comes nowhere close to answering the stated question. I would upvote this if it were made into a real answer. – Jon Dec 12 '13 at 20:11
Also note that with a parameter of type `Expression`, you can't call it using a lambda. – Servy Dec 12 '13 at 20:12
@Gabe added some explanation – vittore Dec 12 '13 at 20:17
@Jon added some details – vittore Dec 12 '13 at 20:18
Why cast it down to an `Expression` just so that you can cast it back up again to a `LambdaExpression`. – Servy Dec 12 '13 at 20:18
@Servy in order to have one method accepting any type of expression as an argument. It could've been method group. – vittore Dec 12 '13 at 20:20
Are you sure about the MemberAccess clause? In particular, what would be the type of the first recursive subcall and why there is "." connecting two recursive subcalls? – Wiktor Zychla Dec 12 '13 at 20:31
@WiktorZychla I wrote this code several years ago, let me check. – vittore Dec 12 '13 at 20:31
@WiktorZychla this should work in case of `a=>a.p1.p2` and return `p1.p2` – vittore Dec 12 '13 at 20:33
Can't check it now but still, I am the only one who upvoted you ;) – Wiktor Zychla Dec 12 '13 at 20:34
@WiktorZychla there is 2 ups and 1 downs :D – vittore Dec 12 '13 at 20:35

score 0 · Answer 2 · answered Dec 12 '13 at 20:17

The signature must involve expression tree rather than func to be able to inspect it. Luckily, your invocations don't change as the compiler will create expressions out of your lambdas.

This version is probably the shortest, it doesn't involve recursion but works only for simple property access lambdas.

public static string MyFunc( Expression<Func<Student, object>> Property )
{
     if ( Property != null && Property.Body != null )
         if ( Property.Body.NodeType == ExpressionType.MemberAccess )
         {
             MemberExpression memberExpression = 
                (MemberExpression)Property.Body;

             if ( !string.IsNullOrEmpty( memberExpression.Member.Name ) )
                 return memberExpression.Member.Name;

         }

     return string.Empty;
 }

score 0 · Answer 3 · edited May 23 '17 at 11:51

0

From another SO question, this may be what you're looking for:

public static string GetPropertyName<T>(Expression<Func<T>> propertyExpression)
{
    return (propertyExpression.Body as MemberExpression).Member.Name;
}

To use it, you'd write something like this:

var propertyName = GetPropertyName(
    () => myObject.AProperty); // returns "AProperty"

edited May 23 '17 at 11:51

Community

1
1

answered Dec 12 '13 at 20:28

Aaron Palmer

8,912
9
48
77

How Func return Object name as string

3 Answers3