Archive, C#, NHibernate

NHibernate Formula Properties

Jason / February 19, 2008

One often overlooked feature of NHibernate is the use of formula properties. Formula properties are properties that do not map to columns in the database, but instead are mapped using raw SQL queries.

The formula is mapped in the NHibernate mapping file using the same property element that normal properties use, just replacing the column keyword for the formula keyword.

<property name="FormulaPropertyName" formula="SQL STATEMENT" /> 

The basic idea is that when NHibernate loads your object it will issue your custom SQL at the same time, allowing for complex read-only properties to offload their work to the database.

For example, assume you have an class representing an order on an e-commerce website. An order is typically composed of line items, and a common question to ask the order as a whole is “what is your subtotal?”. Without weighing the pros and cons of such a decision assume that you do not want to store the subtotal as a field on the order table.

A perfectly acceptable solution would be to have a read-only property as such:

public decimal SubTotal{ get{ decimal subTotal = 0; foreach(LineItem li in this.LineItems){ subTotal += li.ExtendedPrice; //i.e., units ordered times unit price. } return subTotal; } } read more

.NET, Archive, C#, Software Design

Parsing RSS From C#

I set out to write a RSS parser in C#. I know that several existing libraries are available for .NET that parse RSS streams, but out of curiosity I wanted to give it a go anyway.
Before I get started, for those interested in RSS libraries for .NET checkout RSS.NET or RSSConnect, to just name two.

As .NET developers we have some really powerful tools available to us that are built directly into the .NET framework. Take, for example, Serialization. In .NET we can turn an object into an XML resource using the XmlSerializer class, provided that the class is Serializable. In fact, the XmlSerializer object will even attempt to populate an object from an XML resource.

Visual Studio ships with a tool called XSD which can turn an XML Schema Definition into a C# class. Knowing that RSS is expressed as an XML resource, I set out to find an XSD for RSS. After some searching I found this site, which contains an XSD for RSS that the site’s author wrote. For posterity I have placed a mirror of that file on my own site, which you can find here.

Before continuing on, I need to pause and look ahead. The XSD that I found did not work out of the box, and I had to make a small modification to get it to work. I removed a reference to the RSS schema namespace from the XSD. The modified XSD can be downloaded from here

Now, armed with an XSD, we can have the XSD program make some classes for us. From a command prompt (preferable the “Visual Studio Command Prompt” command prompt) type:

xsd RSS20.xsd /classes

Provided that RSS20.xsd is the name of the RSS XSD, and that you are currently in the same directory as RSS20.xsd, the XSD program should output a single file called RSS20.cs. The C# source file that XSD produced contains a class definition for each RSS entity, most notable the root node called “rss”.

With classes that represent RSS, we can now use the XmlSerializer object to easily populate an object with RSS data. For example:

     string rssXml = "... your rss data here ...";
XmlSerializer helper = new XmlSerializer(typeof(rss));
rss obj = (rss)helper.Deserialize(new StringReader(rssXml));

The above code snippet, will create an rss instance called “obj” from raw RSS data. But, you don’t want to have to do this everytime you want to parse RSS. Instead, it would be helpful if that logic was encapsulated by the rss object. Fortunately, the classes produced by the XSD program are all partial classes. So, in a separate .cs file, we can re-declare the rss class and expand upon its functionality.

//declare another portion of the "rss" object.
public partial class rss{
//add more methods to "rss" here
read more

.NET, Archive, ASP.NET, aspNETserve, C#

An Embedded ASP.NET Web Server

To correspond with the release of aspNETserve version 1.1, I have written a simple demonstration of hosting an ASP.NET 2.0 web server right into your own application.

The following code sample is about as simple as it gets.

using System; using System.Collections.Generic; using System.Text; using aspNETserve; namespace ConsoleWebServer { class Program { static void Main(string[] args) { string physicalPath = "c:\\wwwroot"; int port = 8080; using (Server s = new Server(new System.Net.IPAddress(new byte[] { 127, 0, 0, 1 }), "/", physicalPath, port)) { s.Start(); Console.WriteLine("Press any key to stop the server"); Console.ReadKey(); s.Stop(); } } } } read more

.NET, Archive, C#

Tail Recursion Revisited

A year ago I blogged about Tail Recursion in C# on .NET 2.0. With the public beta of .NET 3.5 now available, I decided to retry my little experiment.

For the experiment I used Beta 1 of .NET 3.5 (version 3.5.20404), which you can get from here. Using the supplied compiler, I compiled the following C# code:

public class TailTest{ public static void Main(){ TailTest f = new TailTest(); f.DoTail(0); } public void DoTail(int n){ int v = n + 1; System.Console.WriteLine(v); DoTail(v); } } read more

.NET, Archive, C#

Throwing More Than Just Exceptions

Jason / January 23, 2007

It is a little known fact (and probably for the best) that the CLR can throw and catch more than just System.Exception and its children. In fact, the CLR can use any type as if it was an Exception.

.assembly ExceptionTestAssembly {}

.class public ExceptionTest { //custom class
//note that ExceptionTest does NOT extend System.Exception
.method public void .ctor(){
.maxstack 1

.method static void main() il managed{
.entrypoint //program entry point...
.try {
newobj instance void ExceptionTest::.ctor()
throw //throw a random object

} catch ExceptionTest { //catch the random object
ldstr "Random object caught"
call void [mscorlib]System.Console::WriteLine(string)
leave.s OUT

OUT: ret
read more

Archive, C#, XNA

Embedding Assets Into Your XNA Game

Jason / January 21, 2007

Currently I am a working on a small XNA project whose solution is composed of 4 projects, a DLL, a Windows Game, a Xbox 360 game, and a level editor. Each projects needs access to my assets (currently just 2d sprites), and has raised the interesting question of how to easily share them between each project.

What I had been doing was adding the assets to the Windows game as pipeline content. After compiling it I would then copy the compiled assets from the bin directory, to the bin directories of the level editor and the Xbox 360 game. While this worked, it was error prone and time consuming.

Instead I found that I can add my assets to the DLL as embedded content, and then load them at runtime. Normally you would have probably loaded content by calling the "Load" method of "ContentManager", like:


As stated above, the problem with this solution is that "mySprite" would have had to been compiled into the content pipeline. When your assets are added as embedded content, the above method does not work. Instead, you can load your content like this:

Assembly asm = Assembly.GetExecutingAssembly();
Texture2D.FromFile(_graphicsDevice, asm.GetManifestResourceStream("SampleProject.Textures.mySprite.png"));
read more

.NET, Archive, ASP.NET, C#

Cookie Renaming in ASP.NET

Jason / January 20, 2007

In ASP.NET you can seamlessly rename cookies on the fly with the help the PreSendRequestHeaders and BeginRequest events of the HttpApplication class.

Both events call EventArgs delegates, with the sender object as a HttpApplication instance.


/// Called when a cookie is about to be sent to the browser. /// private void CookieOut(object sender, EventArgs e) { HttpApplication app = (HttpApplication)sender; HttpCookie cookie = app.Response.Cookies["ASP.NET_SessionId"]; if (cookie != null) { app.Response.Cookies.Remove("ASP.NET_SessionId"); cookie.Name = "fooBar"; app.Response.Cookies.Add(cookie); } } read more