Published
Wednesday, October 03, 2007 3:05 AM
by
mtaulty
I've written probably 10 - 20 different little applications that I try to use to highlight the differences between IQueryable and IEnumerable previously and, just recently, I've written another one.
I think this is a really interesting piece of code. Take it, compile it (in VS 2008) and press F10. Now, continue to press F11 until the program stops - repeat until satisfied with what's going on. I find the iterators aspect of it all quite entertaining as the debugger appears to step into functions in the wrong order.
using System;
using System.Collections.Generic;
using System.Collections;
class Program
{
static void Main(string[] args)
{
Console.ForegroundColor = ConsoleColor.Yellow;
Console.WriteLine("Enumerable...");
#region Enumerable
IEnumerable<int> enumerable =
new List<int>() { 10, 20, 30, 40, 50 };
var query = from i in enumerable
where i > 20
select i * 2;
// Enumerate to get the operators to do their work
foreach (var result in query)
{
}
#endregion
Console.ForegroundColor = ConsoleColor.Green;
Console.WriteLine("\nQueryable");
#region Queryable
System.Linq.IQueryable<int> queryable =
System.Linq.Queryable.AsQueryable(enumerable);
query = from i in queryable
where i > 20
select i * 2;
// Enumerator to get the operators to do their work
foreach (var result in query)
{
}
#endregion
}
}
public static class Extensions
{
public static IEnumerable<R> Select<R, T>(this IEnumerable<T> list,
Func<T, R> selector)
{
Console.WriteLine("SELECT starting...");
foreach (var v in list)
{
Console.WriteLine("\tSELECT returning item...");
yield return (selector(v));
}
Console.WriteLine("SELECT finished.");
}
public static IEnumerable<T> Where<T>(this IEnumerable<T> list,
Predicate<T> predicate)
{
Console.WriteLine("WHERE starting...");
foreach (var v in list)
{
Console.WriteLine("\tWHERE returning item...");
if (predicate(v))
{
yield return (v);
}
}
Console.WriteLine("WHERE finished.");
}
public static System.Linq.IQueryable<R> Select<R, T>(this System.Linq.IQueryable<T> list,
System.Linq.Expressions.Expression<Func<T, R>> selector)
{
Console.WriteLine("SELECT called with [{0}]", selector);
Console.WriteLine(" Inner clause [{0}]", list.Expression);
Console.WriteLine();
return (System.Linq.Queryable.Select<T,R>(list, selector));
}
public static System.Linq.IQueryable<T> Where<T>(this System.Linq.IQueryable<T> list,
System.Linq.Expressions.Expression<Func<T,bool>> predicate)
{
return (System.Linq.Queryable.Where<T>(list, predicate));
}
}