Look Ma! No Classes – Creating Generic List(T) collection of Anonymous Types and calling Extension Methods

Posted by: Suprotim Agarwal , on 12/26/2008, in Category LINQ
Views: 46417
Abstract: In this article, we will see how to create Generic List(T) collection of Anonymous Types using LINQ in C# and VB.NET. We will also explore Extension Methods and see how to call them using AnonymousTypes
Look Ma! No Classes – Creating Generic List(T) collection of Anonymous Types and calling Extension Methods
 
In one of my previous articles, I explained some Common Generic List(T) Operations using C# 2.0 and VB.NET . However the approach was very specific to a List<T> collection that we pre-created. What if we wanted to create classes on the fly, create a collection of the class and also add some custom generic functionality? In this article, we will explore how to create collection of Anonymous Types and also call Extension Methods.
For those who are not familiar with Anonymous types and Extension Methods, please read the new features of C# 3.0 and in VB.NET. In simple words, Anonymous Types enables creation of unnamed types on the fly without first writing the definition of the type.
Since this article also focuses on creating a List(T) collection of Anonymous Types, I will be creating a Helper class (TypeCreator) that will return me a List(T) of anonymous type using generic type inference.
Note: If you see the possibility of passing in your type across layers or services, give it a structure.
Create a Console Application Project and add a class called ‘TypeCreator’. The code will look similar to as shown below. This code template returns a List(T) collection:
C#
    static class TypeCreator
    {
        public static List<T> TypeGenerator<T>(this T[] t)
        {
            return new List<T>(t);
        }
    }
VB.NET
Module TypeCreator
    Public Function TypeGenerator(Of T)(ByVal at As T()) As List(Of T)
        Return New List(Of T)(at)
    End Function
 
End Module
In order to call this TypeGenerator function, add the following code in the Main() method of your Program.cs/Module1.vb as shown below:
C#
        static void Main(string[] args)
        {
            var Person = TypeCreator.TypeGenerator(new[]{
                new {ID=1, FirstName="John", MiddleName="", LastName="Shields", Age=29, Sex='M'},
                new {ID=2, FirstName="Mary", MiddleName="Matthew",  LastName="Shields", Age=29, Sex='M'},
                new {ID=3, FirstName="Amber", MiddleName="Carl", LastName="Shields", Age=29, Sex='M'},
                new {ID=4, FirstName="Kathy", MiddleName="", LastName="Shields", Age=29, Sex='M'}
            });
             }
VB.NET
    Sub Main()
        Dim Person = TypeCreator.TypeGenerator(New Object() { _
            New With {.ID = 1, .FirstName = "John", .MiddleName = "", .LastName = "Shields", .Age = 29, .Sex = "M"c}, _
            New With {.ID = 2, .FirstName = "Mary", .MiddleName = "Matthew", .LastName = "Shields", .Age = 29, .Sex = "M"c}, _
            New With {.ID = 3, .FirstName = "Amber", .MiddleName = "Carl", .LastName = "Shields", .Age = 29, .Sex = "M"c}, _
            New With {.ID = 4, .FirstName = "Kathy", .MiddleName = "", .LastName = "Shields", .Age = 29, .Sex = "M"c}})
 
    End Sub
As evident in the code above, we are creating a List(T) collection of anonymous types by passing anonymous classes to the TypeGenerator() function. How do we test it? We can surely use for each loop and then print the collection members on the console. But what I would like to do, is just call something like MyColl.PrintToConsole() and that’s it. I want to encapsulate the looping mechanism as well as be able to pass in any List(T) collection of anonymous types to be looped. Enter Extension Methods!
Extension Methods are static methods that extend existing classes and can be invoked by using instance method syntax.
We will extend the ‘TypeCreator’ class and add in an Extension Method called ‘PrintToConsole’. The PrintToConsole method uses reflection to extract the properties(name, value) of the List(T) passed to it. The code will look similar to the following:
C#
        public static void PrintToConsole<T>(this List<T> items)
        {
            PropertyInfo[] pi = typeof(T).GetProperties();
            // extra loop required to print column names only once
            foreach (var p in pi)
            {
                Console.Write("{0,-12}", p.Name);
            }
            Console.WriteLine();
            foreach (var item in items)
            {               
                foreach (var p in pi)
                {
                    Console.Write("{0,-12}", p.GetValue(item, null));
                }
                Console.WriteLine();
            }
            Console.ReadLine();
        } 
VB.NET
<System.Runtime.CompilerServices.Extension()> _
    Public Sub PrintToConsole(Of T)(ByRef items As List(Of T))
        Dim pi As PropertyInfo() = GetType(T).GetProperties()
        ' extra loop required to print column names only once
        For Each p In pi
            Console.Write("{0,-12}", p.Name)
        Next
        Console.WriteLine()
        For Each item In items
            For Each p In pi
                Console.Write("{0,-12}", p.GetValue(item, Nothing))
            Next
            Console.WriteLine()
        Next
        Console.ReadLine()
    End Sub
Now all you have to do in your Main() method is to call this ‘Extension Method’
Person.PrintToConsole();
In order to test if this Extension Method is generic enough, just try creating a few more anonymous type collections and pass it to the ‘PrintToConsole’. That’s it.
The entire source code will look similar to the following:
C#
Program.cs
using System;
using System.Collections.Generic;
using System.Text;
using System.Linq;
 
namespace CommonGenericOperationsUsingLINQ
{
    class Program
    {
       
        static void Main(string[] args)
        {
            var Person = TypeCreator.TypeGenerator(new[]{
                new {ID=1, FirstName="John", MiddleName="", LastName="Shields", Age=29, Sex='M'},
                new {ID=2, FirstName="Mary", MiddleName="Matthew", LastName="Shields", Age=29, Sex='M'},
                new {ID=3, FirstName="Amber", MiddleName="Carl", LastName="Shields", Age=29, Sex='M'},
                new {ID=4, FirstName="Kathy", MiddleName="", LastName="Shields", Age=29, Sex='M'}
            });
                          
            Person.PrintToConsole();
 
            var Products = TypeCreator.TypeGenerator(new[]{
                new {PID=1, ProductName="Chai", Quantity=12, Price=18.10},
                new {PID=2, ProductName="Coffee",Quantity=23 , Price=28.20},
                new {PID=3, ProductName="Chains", Quantity=42,   Price=21.60},
                new {PID=4, ProductName="Chips", Quantity=21, Price=21.20}
            });
 
            Products.PrintToConsole();       
 
        }
    }
}
 
TypeCreator.cs
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Reflection;
 
namespace CommonGenericOperationsUsingLINQ
{
    static class TypeCreator
    {
        public static List<T> TypeGenerator<T>(this T[] at)
        {
            return new List<T>(at);
        }
 
        public static void PrintToConsole<T>(this List<T> items)
        {
            PropertyInfo[] pi = typeof(T).GetProperties();
            // extra loop required to print column names only once
            foreach (var p in pi)
            {
                Console.Write("{0,-12}", p.Name);
            }
            Console.WriteLine();
            foreach (var item in items)
            {               
                foreach (var p in pi)
                {
                    Console.Write("{0,-12}", p.GetValue(item, null));
                }
                Console.WriteLine();
            }
            Console.ReadLine();
        }       
    }
}
 
VB.NET
Module1.vb
Module Module1
 
    Sub Main()
        Dim Person = TypeCreator.TypeGenerator(New Object() { _
            New With {.ID = 1, .FirstName = "John", .MiddleName = "", .LastName = "Shields", .Age = 29, .Sex = "M"c}, _
            New With {.ID = 2, .FirstName = "Mary", .MiddleName = "Matthew", .LastName = "Shields", .Age = 29, .Sex = "M"c}, _
            New With {.ID = 3, .FirstName = "Amber", .MiddleName = "Carl", .LastName = "Shields", .Age = 29, .Sex = "M"c}, _
            New With {.ID = 4, .FirstName = "Kathy", .MiddleName = "", .LastName = "Shields", .Age = 29, .Sex = "M"c}})
 
        Person.PrintToConsole()
 
        Dim Products = TypeCreator.TypeGenerator(New Object() { _
             New With {.PID = 1, .ProductName = "Chai", .Quantity = 12, .Price = 18.1}, _
             New With {.PID = 2, .ProductName = "Coffee", .Quantity = 23, .Price = 28.2}, _
             New With {.PID = 3, .ProductName = "Chains", .Quantity = 42, .Price = 21.6}, _
             New With {.PID = 4, .ProductName = "Chips", .Quantity = 21, .Price = 21.2}})
 
        Products.PrintToConsole()
    End Sub
 
End Module
 
TypeCreator.vb
Imports System.Reflection
 
Module TypeCreator
    Public Function TypeGenerator(Of T)(ByRef at As T()) As List(Of T)
        Return New List(Of T)(at)
    End Function
 
    <System.Runtime.CompilerServices.Extension()> _
    Public Sub PrintToConsole(Of T)(ByVal items As List(Of T))
        Dim pi As PropertyInfo() = GetType(T).GetProperties()
        ' extra loop required to print column names only once
        For Each p In pi
            Console.Write("{0,-12}", p.Name)
        Next
        Console.WriteLine()
        For Each item In items
            For Each p In pi
                Console.Write("{0,-12}", p.GetValue(item, Nothing))
            Next
            Console.WriteLine()
        Next
        Console.ReadLine()
    End Sub
End Module
 
The entire source code in C# and VB.NET can be downloaded from here. I hope this article was useful and I thank you for viewing it.
Give a +1 to this article if you think it was well written. Thanks!
Recommended Articles
Suprotim Agarwal, ASP.NET Architecture MVP, MCSD, MCAD, MCDBA, MCSE, is the CEO of A2Z Knowledge Visuals Pvt. He primarily works as an Architect Consultant and provides consultancy on how to design and develop .NET centric database solutions.

Suprotim is the founder and primary contributor to DotNetCurry, DNC .NET Magazine, SQLServerCurry and DevCurry. He has also written an EBook 51 Recipes using jQuery with ASP.NET Controls. and is authoring another one at The Absolutely Awesome jQuery CookBook.

Follow him on twitter @suprotimagarwal


Page copy protected against web site content infringement by Copyscape


User Feedback
Comment posted by Kevin Gallagher on Wednesday, August 10, 2011 4:52 PM
I could not get PrintToConsole to output and replace it with the following (VB.NET)
    <System.Runtime.CompilerServices.Extension()> _
    Public Sub PrintToConsole(Of T)(ByVal value As IEnumerable(Of T))
        Dim firstRecord = value.First

        For Each pi In firstRecord.GetType.GetProperties
            Console.Write("{0,-12}", pi.Name)
        Next

        Console.WriteLine()

        For Each result In value
            For Each pi In result.GetType.GetProperties
                Console.Write("{0,-12}", pi.GetValue(result, Nothing))
            Next
            Console.WriteLine()
        Next

    End Sub

Post your comment
Name:  
E-mail: (Will not be displayed)
Comment:
Insert Cancel