Linq Reflection Expression throws exception on property of proprety

The error is that you are passing Person into prop.GetValue when accessing PersonName.First. The method tries to get the property First from Person but can't any. You need to pass the correct object into prop.GetValue. I made this generic method which achives what you want. One limitation is that it only checks fields and properties, i will try to add methods in a bit

public static void OutputField < T > (T item, Expression < Func < T, string >> outExpr) 
{
  // Get the expression as string
  var str = outExpr.ToString();

  // Get the variable of the expresion (m, m => ...)
  string pObj = str.Substring(0, str.IndexOf(' '));

  // Get all the members in the experesion (Name, First | m.Name.First);
  string[] members = new string(str.Skip(pObj.Length * 2 + 5).ToArray()).Split('.');

  // Last object in the tree
  object lastMember = item;
  // The type of lastMember
  Type lastType = typeof(T);

  // Loop thru each member in members
  for (int i = 0; i < members.Length; i++) 
  {
    // Get the property value
    var prop = lastType.GetProperty(members[i]);
    // Get the field value
    var field = lastType.GetField(members[i]);

    // Get the correct one and set it as last member
    if (prop is null) 
    {
      lastMember = field.GetValue(lastMember);
    }
    else 
    {
      lastMember = prop.GetValue(lastMember, null);
    }

    // Set the type of the last member
    lastType = lastMember.GetType();
  }

  // Print the value
  Console.WriteLine($ "value={lastMember}");
}

EDIT: Turns out you can compile the expression and invoke it

public static void OutputField<T>(T item, Expression<Func<T, string>> outExpr)
{
  Console.WriteLine($"value={outExpr.Compile().Invoke(item)}");
}