Dynamics and ExpandoObject

Dave Mateer — Thu, 06 Oct 2011 20:23:30 GMT

Whilst getting my head around Rob Conery’s Massive ORM, I needed to figure out what the dynamic keyword is in C#4:

class Program {

 static void Main(string[]
args) {

 Calculator calc = new Calculator();

 int sum = calc.Add(1, 2);

 Console.WriteLine(sum);

 Console.ReadLine();

 }

 }

 public class Calculator {

 public int Add(int a, int b)
{

 return a+b;

 }

 }

creation of an object, invokation of a method, and the collection of a return value

Var

Can represent any type that can be determined at compile time.

class Program {
static void Main(string[] args) {
//int
var i = 5;
//string
var x = "hello";
//int[]
var y = new[] { 0, 1, 2, 3 };
//anonymous type
var anon = new { Name = "Dave", Age = 34 };
//List<int>
var list = new List<int>();
//Calculator
var calc = new Calculator();
int sum = calc.Add(1, 2);
Console.WriteLine(sum);
Console.ReadLine();
}
}

public class Calculator {
public int Add(int a, int b) {
return a+b;
}
}

Dynamic

at runtime you get the type

 class Program {

 static void Main(string[]
args) {

 //int

 dynamic i = 5;

 //string

 dynamic x = "hello";

 //int[]

 dynamic y = new[]
{ 0, 2, 3, 4 };

 //anonymous type

 dynamic anon = new {Name="Dave",
Age=34};

 Console.WriteLine(i + x);

 dynamic calc = new Calculator();

 //don't get intellisense
when press .

 int sum = calc.Add(1, 2);

 Console.WriteLine(sum);

 Console.ReadLine();

 }

 }

 public class Calculator {

 public int Add(int a, int b)
{

 return a+b;

 }

 }

ExpandoObject and TryInvokeMember

An object whose members can be dynamically added and removed at runtime.

can’t do anything with the expandoObject though!

Much better. Saying to the compiler – “Playing with a different set of rules”.

Why doesn’t Product need to by Dynamic?

 dynamic tbl = new DynamicModel("Northwind", "Products", "ProductID");

 //tbl.Single returns
a dynamic of type ExpandoOnject, not an ExpandoObject.

 //acutally an IEnumrable<dynamic>.FirstOfDefault()

 var product = tbl.Single();