Great .NET posters at 9:19 AM

[Change note: The URL of those .NET posters has been changed]

"Barone, Budge & Dominick" has a great collection of posters relating to.NET technology. You can find the first page Here.

.NET web service tips at 11:34 AM

Here are list of tips for .NET web service development. I put here so that I need not google to find them later. :)

1) Generate web service interface so that we can separate implementation from WSDL. When WSDL is changed someday, we will not lose our implemenation code:

wsdl.exe /si ServerInterfaceSample.wsdl

2) Web service can use ASP.NET session state. To enable ASP.NET session state, set WebMethod.EnableSession = True. On the client you must also create a new instance of System.Net.CookieContainer. Note that to persist data for the entire application, neither step is required.

Client code:

//On the client you must add the following code (for session state only):
serviceName.CookieContainer = new System.Net.CookieContainer();

Server code:

 //Setting EnableSession to true allows state to be persisted per Session
[WebMethod(EnableSession=true)]
public String UpdateSessionHitCounter() {
   //update the session "HitCounter" here
   return Session["HitCounter"].ToString();
}

3) Asynchronous call to web service:
Use the event-based model to asynchronously call your Web services.

   //First implement the HelloWorldCompleted method using the following signature:
  //public void HelloWorldCompleted(object sender, HelloWorldCompletedEventArgs args)
 
  //Create the Web service
  HelloWorldWaitService service = new HelloWorldWaitService();
  //Add our callback function to the event handler
  service.HelloWorldCompleted += this.HelloWorldCompleted;
  //Call the Web service asynchronously
  service.HelloWorldAsync("first call");
  //when the Web service call returns the HelloWorldCompleted method will be called

Optimistic Concurrency Control using RowVersion in Sql 2005 and C# at 1:36 PM

To use optimistic concurrency control, one option is to add a RowVersion (kind of timeStamp) column in Sql 2005 table. Its value will be modified automatically by Sql server whenever the row is updated.

alter table dbo.authors add LastRowVersion RowVersion

The type of the newly added column is "TimeStamp" in Sql 2005, but its value has no relationship with time at all. The RowVersion column only uses the same structure of TimeStamp to save version number (8 bytes).

The process of optimistic concurrency control using RowVersion column is like below: When user A gets a record and tried to edit, the RowVersion value is also got to A's program. Another user B also gets the same record to edit, but B saves his/her content before A saves. Now the record's LastRowVersion is changed. When A tries to save content into the record, the save process should compare the previously fetched LastRowVersion with the latest value in the database. If the two values do not match, user A should get error message like "Another user has saved the content in front of you. Your content cannot be saved", blah blah.

Now, let's see how to deal with the RowVersion column in ASP.NET/C# code. In data access layer, we still use SqlDbType.Timestamp for RowVersion to transfer value between our code and Sql Server. But in other layers, we should use byte[] array.

When the ASP.NET page gets the data from business layer, the RowVersion value can be saved in ViewState:

ViewState["RowVersion"] =
Convert.ToBase64String(bo.LastRowVersion);

When user clicks "Save" button in edit page to save changes, we can get the old RowVersion from ViewState in postback:

byte[] rowVersion =
Convert.FromBase64String(ViewState["RowVersion"] as string);

Then we can pass the rowVersion variable with the new content to data access layer for concurrency check as mentioned above.

In some applications, ViewState may be disabled. In this case, we can save the value in ControlState, which needs several more lines of code than using ViewState.

Mix'06 sessions are online now :) at 10:40 AM

Luckily I attended Microsoft Mix'06 conference in Las Vegas in March, 2006. As the conference included various topics covering web design, web development, smart client application, next generation of OS and browser, so the conference was named Mix (mixture).

I was quite impressed by the demos of Windows Presentation Foundation, Windows Presentation Foundation Everywhere, and Atlas. I think other sessions must be also interesting, such as "building your own search engine", but I couldn't attend those meetings at that time.

But now, I can watch all those sessions online :)