Unable to cast object - linq

Question

I am new to LINQ, I tried to run the following code and I got InvalidCastException error: "Unable to cast object of type 'd__3a`1[debug.Product]' to type 'debug.Product'" - what is wrong?
Code (VB - using VS2008)
Private Sub btnLinq_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnLinq.Click
Dim Products As New List(Of Product)
Dim p1 As New Product
p1._ID = "1"
p1._Name = "Product A"
Products.Add(p1)
Dim p2 As New Product
p2._ID = "2"
p2._Name = "Product B"
Products.Add(p2)
Dim p3 As New Product
p3._ID = "3"
p3._Name = "Product C"
Products.Add(p3)
Dim prod As Product = From p In Products Where p._ID = "1" Select p Take 1
MsgBox(prod._ID)
End Sub
End Class
Public Class Product
Public _ID As String
Public _Name As String
End Class

Answer 1

Take returns an IEnumerable<Product> (in your case), and not a Product.
(Check it by outputting result.GetType() ):
(note that my example code is in C#)
List<Product> products = new List<Product> ();
products.Add (new Product ()
{
Id = 1,
Name = "Prod1"
});
products.Add (new Product ()
{
Id = 2,
Name = "Prod2"
});
var result = ( from p in products
where p.Id == 1
select p ).Take (1);
Console.WriteLine (result.GetType ());
Console.ReadLine ();
In my case, the code above outputs:
System.Linq.Enumerable+<TakeIterator>d__3a`1[LinqTest.Product]
In your case, instead of using Take 1, you could try to use First or FirstOrDefault instead.
So, try this:
var result = ( from p in products
where p.Id == 1
select p ).FirstOrDefault ();
Console.WriteLine (result.GetType ());
Console.WriteLine (result.Name);

Answer 2

The Take method (Enumerable.Take) doesn't return an element, rather it returns an another sequence (IEnumerable<Product>). Take(n) just creates a new sequence with a maximum of n elements.
To take the first element from the sequence use one of the following methods:
FirstOrDefault() - returns null if the sequence is empty
First() - throws InvalidOperationException if the sequence is empty