Expression> how can i get TValue's name?

.net c# expression-trees

Question

//ModelFor(person =>person.Name);
public void ModelFor<TModel, TValue>(
    Expression<Func<TModel, TValue>> expression)
{
    //Result should be "Name"
    string nameOfTValue = ????;     
}

Accepted Answer

EDIT: After your edit, I think you are want the name of the member involved in the expression, assuming of course that the expression is a member-expression in the first place.

((MemberExpression)expression.Body).Member.Name

To be more robust, you can do:

var memberEx = expression.Body as MemberExpression;

if (memberEx == null)
     throw new ArgumentException("Body not a member-expression.");

string name = memberEx.Member.Name;

(Not relevant anymore):

To get a System.Type that represents the type of the TValue type-argument, you can use the typeof operator.

You probably want:

typeof(TValue).Name

But also consider the FullName and AssemblyQualifiedName properties if appropriate.

This really has nothing to do with expression-trees; you can use this technique to get the type of a type-argument for any generic method.


Popular Answer

@Ani: I don't think this is right, I think that he wants the name of the parameter in the expression of type TValue

If this is true... this works 1 level deep only but might be handy anyway:

var nameOfTValue = ((MemberExpression)expression.Body).Member.Name; 

Here is smarter implementation that should be able to deal with multiple levels:

 public class PropertyName{
    public static string For<T>(
      Expression<Func<T,object>> expression){
      var body=expression.Body;
      return GetMemberName(body);
    }
    public static string For(
      Expression<Func<object>> expression){
      var body=expression.Body;
      return GetMemberName(body);
    }
    public static string GetMemberName(
      Expression expression){
      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));
    }
  }

Usage:

var fieldName=PropertyName.For<Customer>(x=>x.Address.Region);
//fieldName==Address.Region

Another trick, this can be combined with reflection nicely:

public static T Set<T,TProp>(this T o,
   Expression<Func<T,TProp>> field,TProp value){
  var fn=((MemberExpression)field.Body).Member.Name;
  o.GetType().GetProperty(fn).SetValue(o,value,null);
  return o;
}

Allows to directly set properties with ease, can be useful for test fixtures:

var customer=new Customer("firstName","lastName");
customer.Set(x=>x.Name, "different firstName");


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