First Bulgarian .NET Book is here

Second volume from the first Bulgarian book about .NET is out. You can download free copy from here. Printed version will be available after a month.

Windows Forms data binding and notification of changed properties

Yesterday a college of mine asked me a question: "How to refresh TextBox control in Windows forms application binded to a property of object, when the property change its value?". The solution is very simple, but according to me not very well documented (at least in books I read).

Solution: Provide event named PropertyNameChanged, where PropertyName is the name of property binded to the TextBox. During the binding process, the text box inspects binded object for event with the mentioned signature and binds to it. The sample code looks like this:

public class Customer

{

    private string mName;

    public string Name

    {

        get { return mName; }

        set

        {

            mName = value;

            if (NameChanged != null)

            {

                NameChanged(this, EventArgs.Empty);

            }

        }

    }

    public event EventHandler NameChanged;

}

Customer cust = new Customer();

textBox1.DataBindings.Add("Text", cust, "Name");

Another possible solution is to remove and add binding of the text box to the object. You can write general routine to loop through each control for a given form and remove-add binding. This is nasty solution of course.

Cool conference in Bulgaria

DevReach - one of the most exiting conferences about Microsoft technologies in Bulgaria is coming. According to the program, some of the world leading industry speakers will present quite interesting lectures. Hope we will meet there.

Google toolbar 4

This morning I was amazed! A few minutes after turning on my PC a small balloon appeared. The message in the balloon was something about Google toolbar update. Who cares, was my first reaction. But when the update was finished I was surprised to learn that LONG WAITING FEATURES LIKE ACCESSING BOOKMARKS FROM ANY COMPUTER are already present. Believe me - this is like a elixir of life for me. I'm using one PC at work, one PC at home and one laptop. Managing bookmarks in situation like this is almost nightmare. In the past there were some other decision of this problem, but none of them was so elegant as Google toolbar. BTW, Microsoft are developing the same service, but as far as I know this feature is still in beta.
The other features I like are SpellCheck and Translate. If you are inspired, install the toolbar from here for WinXP and IE. Enjoy!

ADO.NET Entity Framework ContextObject and ASP.NET application

Last month Microsoft published first CTP of ADO.NET Entity Framework. For more info - look here. Although Microsoft is still planning integration between Entity Framework and ASP.NET, I want to show you how to handle ADO.NET Entity Framewrok context object in ASP.NET application. This post is inspired from NHibernate session management.
The idea is simple: Context object will be stored in ASP.NET session and after the request HTTPModule will free it. I'm using ASP.NET session instead of ASP.NET context to further extend this example to support session per application transaction strategy. If you are wondering what is "session per application transaction" take a look at NHibernate session management. Here is the code of the implementation:

public class ContextManager<T>where T: ObjectContext, new()

{

    public static T ObjectContext

    {

        get

        {

            T resultContext;

            if (HttpContext.Current.Items.Contains(

                ContextConst.CONTEXT_OBJECT_SESSION_KEY))

            {

                resultContext =

                    (T)HttpContext.Current.Items[

                        ContextConst.CONTEXT_OBJECT_SESSION_KEY];

            }

            else

            {

                resultContext = new T();

                HttpContext.Current.Items[ContextConst.CONTEXT_OBJECT_SESSION_KEY] = 

                    resultContext;

            }

            return resultContext;

        }

    }

    public static bool isActiveObjectContext

    {

        get

        { 

            return HttpContext.Current.Items.Contains(

                ContextConst.CONTEXT_OBJECT_SESSION_KEY);

        }

    }

 }

public class ContextHttpModule : IHttpModule 

{

    #region IHttpModule Members

    public void Init(HttpApplication context)

    {

        context.EndRequest += new EventHandler(OnEndRequest);

    }

    public void Dispose()

    {

        //Intentionaly not implemented

    }

    public void OnEndRequest(Object sender, EventArgs e)

    {

        if (HttpContext.Current.Items.Contains(ContextConst.CONTEXT_OBJECT_SESSION_KEY))

        {

            ObjectContext contextObject = 

                (ObjectContext)HttpContext.Current.Items[

                    ContextConst.CONTEXT_OBJECT_SESSION_KEY];

            contextObject.Dispose();

        }

    }

    #endregion

}

internal class ContextConst

{

    public const string CONTEXT_OBJECT_SESSION_KEY =

        "ContextConst.CONTEXT_OBJECT_SESSION_KEY";

}

Now, lets look how the code above can be used. First lets make some corrections to web.config file:

<connectionStrings>

  <add name="Duwamish7Model.Duwamish7" 

       connectionString="metadata=C:\Temp\ContextObject\Model;

          mapping=C:\Temp\ContextObject\Model;

          provider=System.Data.SqlClient;

          provider connection string="Data Source=ns-server;

          Initial Catalog=Duwamish7;Integrated Security=True""

    providerName="System.Data.Mapping" />

</connectionStrings>

<httpModules>

  <add name="ContextObjectManager"

       type="ObjectContextManager.ContextHttpModule, ObjectContextManager"/>

</httpModules>

Having all of the above done, we can write somethig like this:

Duwamish7 db = ContextManager<Duwamish7>.ObjectContext;

Query<Authors> query = db.GetQuery<Authors>(

    "SELECT VALUE a FROM Authors AS a WHERE a.PKId > 144");

Repeater1.DataSource = query;

Repeater1.DataBind();

P.S. The code above is not tested for concurrency problems.

WCF and WS Eventing

WCF (aka Indigo) is the latest communication technology from Microsoft (still in beta). Although there are a lot of goodies in this technology, something really useful for me is missing - implementation of WS Eventing. If you are wondering why - this article gives the answer. Fortunately there is already non-Microsoft implementation. Read this article if you are interested.

Finally it is true!

Yesterday, PFC Levski Sofia did it. The team had succeeded to qualify for the UEFA champions league group stage for the first time in Bulgarian football history. Although I'm fan of the CSKA Sofia the success of Levski makes me happy. More info - here.

Microsoft SQL Server and Ad-Hock queries optimization

Yesterday I was surprised to learn that Microsoft SQL Server 2005 makes behind the scene parameterization of ad-hock queries. For example, lets have the following query:

SELECT ID, Name FROM Article WHERE Price > 100

SQL Server 2005 will replace constant literal values (100 in this example) by variables and this way query plan will be reuses for all queries similar to

SELECT ID, Name FROM Article WHERE Price > @p1

Not all of the ad-hock queries can be parameterized. If you are interested read this article.

Attribute based transaction management and NHibernate

In my previous post about NHibernate session management I presented a session per request strategy for session management in ASP.NET application. I will extend this example to show you how to declaratively manage transactions via attributes. Take a look at the GenericDAO.Save method:

public void Save(T entity)

{

    bool manageTransaction = ! orm.isActiveTransaction;

    if (manageTransaction)

    {

        orm.BeginTransaction(IsolationLevel.ReadCommitted);

    }

    try

    {

        orm.session.SaveOrUpdate(entity);

        if (manageTransaction)

        {

            orm.CommitTransaction();

        }

    }catch(Exception e)

    {

        if (manageTransaction)

        {

            orm.RollbackTransaction();

        }

        throw e;

    }            

}

Almost 90% of the code is for transaction management. It will be nice if we can write something like:

[Transaction(IsolationLevel.ReadCommitted)]

public void Save(T entity)

{

    mOrm.session.SaveOrUpdate(entity);

    mOrm.session.Flush();

}

To achieve this, I will use Spring.NET to intercept method call of the DAO. Before method marked with TransactionAttribute is executed a transaction will be started and then committed after method is executed. Although .NET provides solution for intercepting method calls via ContextBoundObject, I will use Spring.NET because this way my DAO object must implement just one interface instead of inheriting from ContextBoundObject.
Lets begin with the implementation. First I will declare the attribute used to mark transaction sensitive methods:

[AttributeUsage(AttributeTargets.Method)]

public class TransactionAttribute : Attribute

{

    private IsolationLevel mIsolationLevel;

    public TransactionAttribute()

    {

        mIsolationLevel = IsolationLevel.ReadCommitted;

    }

    public TransactionAttribute(IsolationLevel aIsolation)

    {

        mIsolationLevel = aIsolation;

    }

    public IsolationLevel isolationLevel

    {

        get { return mIsolationLevel; }

        set { mIsolationLevel = value; }

    }

}

Now I will decrare the class responsible for starting and committing transactions. There are a lot of specific issues about method interception and Spring.NET so if you are not familiar with them read the documentation about Spring.NET. The class looks like:

public class TransactionAroundAdvice : IMethodInterceptor

{

    OrmManager mOrm;

    public TransactionAroundAdvice()

    {

        mOrm = OrmManagerFactory.GetInstance();

    }

    private TransactionAttribute GetTransactionAttribute(MethodInfo aMethod)

    {

        object[] attributes = aMethod.GetCustomAttributes(

            typeof(TransactionAttribute), true);

        if (attributes.Length != 1)

        {

            //TODO: Throw more meaningfull exception and message

            throw new Exception("Transaction Attribute is missing");

        }

        return (TransactionAttribute)attributes[0];

    }

    public object Invoke(IMethodInvocation invocation)

    {

        bool manageTransaction = ! mOrm.isActiveTransaction;

        if (manageTransaction)

        {

            TransactionAttribute transactionAttribute =

                GetTransactionAttribute(invocation.Method);

            mOrm.BeginTransaction(transactionAttribute.isolationLevel);

        }

        //TODO: Find way to compare isolation level from TransactionAttribute and

        //current active transaction if manageTransaction == false

        object returnValue;

        try

        {

            returnValue = invocation.Proceed();

            if (manageTransaction)

            {

                mOrm.CommitTransaction();

            }

        }catch(Exception e)

        {

            if (manageTransaction)

            {

                mOrm.RollbackTransaction();

            }

            if ((e is TargetInvocationException) && (e.InnerException != null))

            {

                //Because when AOP is enables, method is invoked via reflection

                //TargetInvocationException is thrown. This exception is most likely

                //to confuse application developer, so it is removed

                throw e.InnerException;

            }

            else

            {

                throw e;

            }

        }            

        return returnValue;

    }

}

When a method marked with TransactionAttribute is intercepted then Invoke method from TransactionAroundAdvice class is called. Now lets see how our DAO class looks like when transaction management code is removed:

public class AttributeEnabledDAO<T>: IDAO<T>

{

    public AttributeEnabledDAO()

    {

        mOrm = OrmManagerFactory.GetInstance();

    }

    private OrmManager mOrm;

    #region IDAO Members

    public T Load(object id)

    {

        return (T) mOrm.session.Load(typeof(T), id);

    }

    [Transaction(IsolationLevel.ReadCommitted)]

    public void Save(T entity)

    {

        mOrm.session.SaveOrUpdate(entity);

        mOrm.session.Flush();

    }

    #endregion

}

Much more simple. Example of using AttributeEnabledDAO is given bellow:

ProxyFactory articleDAOFactory = new ProxyFactory(

    new AttributeEnabledDAO<Article>());

articleDAOFactory.AddAdvisor(new DefaultPointcutAdvisor(

    new AttributeMatchMethodPointcut(typeof(TransactionAttribute)),

    new TransactionAroundAdvice()));

IDAO<Article> articleDao;

lock (synchObject)

{

    articleDao = (IDAO<Article>) articleDAOFactory.GetProxy();

}

Article article = articleDao.Load(1);

article.Name = "Paracetamol";

article.SalePrice = rnd.NextDouble();

articleDao.Save(article);

ADO.NET vNext CTP is out

Microsoft has just released ADO.NET vNext CTP. This CTP includes the preview build of the long waiting ADO.NET Entity Framework. This Entity Framework is Microsoft's ORM tool. If you are wondering what is ORM tool take a look at my post about
NHibernate session management.
Presentation with features of Entity Data Model can be found here. If somehow Link* technologies looks messy for you, taka a look at this presentation.

Querying Microsoft SQL Server trace files

Have you ever wanted to be able to query saved SQL Server profiler trace files (*.trc)? Yes! Then you need to use fn_trace_gettable.