on code

Dependency Injection in Asp.net MVC using MVC Contrib

2010-01-07T05:23:10.037

For the sake of creating the sample let's introduce the dependency of a ILinkRepository in our brand new asp.net MVC application. Eventually this repository will be used by our HomeController to display a number of Links and finally we will inject the dependency by StructureMap dependency framework..

Next we will add the dependency of ILinkRepository on our HomeController. Since the default ControllerFactory cannot cope with controllers having no default constructor we will hard code the initialization of this dependency on the default constructor. Finally we will pass the list of links to the view and the view will display it for the user. This is the common scenario.

Since view is strongly typed, it will just iterate over the collection producing a list of links. We are now done with the basic structure of the application. We have just used a type of dependency injection infamously known as Poor Man's dependency injection since the HomeController constructor hard coded the creation of the repository.

Now, it's time to modify the controller for dependency injection. Since we are using dependency injection, controller is not concerned with creating the repository as in previous version. Dependency injection framework will automatically provide the dependent repository to the controller.

Running the application now will definitely produce an error since the default controller factory cannot create controllers having no parameterless constructor as shown below.

No parameterless constructor defined for this object.

Finally we are in a position to introduce the StructureMap dependency injection framework to the MVC application. It could be configured in the Global.asax.cs file as follows and the application will run as expected.

Source code could be downloaded from here.

DataContract Serializer Essentials

2010-01-07T05:25:16.507

DataContractSerializer could be used to serialize and deserialize instances of a type into an XML stream or document. The first step in the process is to prepare the type for the serialization. In order to apply the DataContract attributes we have to add reference to the assembly System.Runtime.Serialization.dll. Decorate the Type and the members for the Type to be serialized as shown below.

In addition to the implicit serialization, an instance of DataContractSerializer can be used to explicitly serialize the object by using an appropriate object to write the format (an instance of XmlWriter, fro example). The details are illustrated in the following picture.

The resulting XML file could be customized by passing the properties such as Name and Namespace to the DataContract and DataMember attributes.

Getting Started with Clojure in .net

2009-11-05T05:49:47.357

Before getting started here is the pre-requisites for installing ClojureCLR

Microsoft .NET Framework Version 3.5 SP1
Visual Studio 2008 SP1
Dynamic Language Runtime
NUnit
RhinoMocks

These are the steps followed by me for the new installation

Created a folder called ClojureCLR
Downloaded the Dynamic Language Runtime and extracted the DLR_Main folder into the above folder
Compiled the DLR by opening the visual studio solution file inside DLR_Main
Downloaded the ClojureCLR by using the git (Windows version can be downloaded here) and Opened the ClojureCLR.sln file
Added references for NUnit and Rhinomocks (with castle dependencies download from here) Clojure.Tests project
Set Clojure.Main as startup project and then Crl + F5 or F5 will start the interactive Clojure section

Clojure is dynamic i.e,

Clojure can be embedded in .net applications and can be interacted with
Can be used as a scripting language inside .net
Can be interacted with the primary programming interface called Read-Eval-Print (REPL) loop
Supports dynamic compilation

Part of clojure called Reader will read the clojure program in chunks called forms and translates them in to clojure data structures. when run for the first time, the clojure REPL will display the following prompt.


Clojure 1.1.0-alpha-SNAPSHOT
user=>

Prompt displays the default namespace and is ready to evaluate the clojure programs. Let's feed it with a number.


Clojure 1.1.0-alpha-SNAPSHOT
user=> 42 1
42

user=> (+ 2 3)2
5

Number literal 1 is a Form in clojure and evaluates to itself. Let's feed the REPL with a function that calculates the sum of two numbers 2. Several deviations from the imperative programming languages are evident from this single expression.

All program codes are written in parenthesized lists
A function call is written as a list with the function or operator's name (+ in the above code) first, and the arguments following (2 and 3 in above code)
White space is the commas in Clojure (2 3 in the above code as arguments instead of 2, 3)


Clojure 1.1.0-alpha-SNAPSHOT
user=> (+ 4 6) 3
10
user=> (- 5 4) 4
1
user=> (/ 2.0 3) 5
0.666666666666667
user=> (* 5 6) 6
30
user=> (inc 4) 7
5
user=> (dec 4) 8
3
user=> (quot 12 5) 9
2
user=> (rem 12 5) 10
2
user=> (min 2 3 4 1) 11
1
user=> (max 2 3 4 1) 12
4

Add, Subtract, Multiply, Divide, Increment, Decrement, quot[ient] of dividing numerator by denominator, remainder of dividing numerator by denominator, least of the nums and the greatest of the nums are the computations supported by the clojure on Numbers. In addition to the bitwise operations the numbers support the following comparison operations.


Clojure 1.1.0-alpha-SNAPSHOT
user=> (== 1 1)
True
user=> (< 1 2)
True
user=> (<= 3 4)
True
user=> (> 3 2)
True
user=> (>= 4 3)
True
user=> (zero? 4)
False
user=> (pos? -2)
False
user=> (neg? -2)
True

Other data structures will be covered in future posts.

Asp.net MVC Areas in depth - Part 2

2009-10-12T08:42:07.097

One of the first gotchas that will come across while using the asp.net MVC areas is in the usage of same controller name across different areas and the main project. For example the default asp.net MVC template has a HomeController and if we add the HomeController to one of the areas, accessing the home part of the areas will work fine but accessing the main home url will result in the following error

	The controller name 'home' is ambiguous between the following types: 
        AreasInDepth.Controllers.HomeController 
        AreasInDepth.Areas.Blog.Controllers.HomeController

The easiest solution is to come up with unique controller names. Since the routing for the controllers in the areas works fine in this case and the only thing we have to fix is the main controllers we can use another concept to make this code work. The following code in Global.asax file is all that is required to fix this mess

 protected void Application_Start()
 {
      AreaRegistration.RegisterAllAreas();
      RegisterRoutes(RouteTable.Routes);
      ControllerBuilder.Current.DefaultNamespaces.Add("AreasInDepth.Controllers"); 1
 }

Simply, the above code instructs the DefaultControllerFactory to give priority for the controller inside the main project over those in areas and do not throw the previous InvalidOperationException if the controller name is happened to be unique among these default name spaces 1.

It's time to continue exploring the areas in asp.net MVC 2 preview 2

public Route MapRoute(string name, string url, object defaults, object constraints, string[] namespaces) 
{
    if (namespaces == null && Namespaces != null) {
        namespaces = Namespaces.ToArray();
    }

    Route route = Routes.MapRoute(name, url, defaults, constraints, namespaces); 1
    route.DataTokens["area"] = AreaName;2

    bool useNamespaceFallback = (namespaces == null || namespaces.Length == 0);
    route.DataTokens["UseNamespaceFallback"] = useNamespaceFallback; 3

    return route;
}

MapRoute function of the AreaRegistrationContext class, discussed in the previous post, creates and adds 1 a Route to the global static RouteTable.Routes. It also places two data tokens namely area 2 and UseNamespaceFallback 3 which are later utilized in the route mapping workflow. If namespaces are not provided UseNameSpaceFallBack data token will have the value of true and the DefaultControllerFactory will probe the rest of the namespaces to get a valid controller type. This is a useful hook to prevent the DefaultControllerFactory from searching for controller in unintended areas. Rest of the magic happens during the request processing and we have to look the code inside DefaultControllerFactory, and here it is

protected internal virtual Type GetControllerType(RequestContext requestContext, string controllerName) {
    if (String.IsNullOrEmpty(controllerName)) {
        throw new ArgumentException(MvcResources.Common_NullOrEmpty, "controllerName");
    }

   
    object routeNamespacesObj;
    Type match;

     1
    if (requestContext != null && requestContext.RouteData.DataTokens.TryGetValue("Namespaces", out routeNamespacesObj)) 
    {
        IEnumerable routeNamespaces = routeNamespacesObj as IEnumerable;
        if (routeNamespaces != null) {
            HashSet nsHash = new HashSet(routeNamespaces, StringComparer.OrdinalIgnoreCase);
            match = GetControllerTypeWithinNamespaces(controllerName, nsHash);

            
            if (match != null || false.Equals(requestContext.RouteData.DataTokens["UseNamespaceFallback"])) {
                
                return match; 2
            }
        }
    }

    
    HashSet nsDefaults = new HashSet(ControllerBuilder.DefaultNamespaces, StringComparer.OrdinalIgnoreCase);
    match = GetControllerTypeWithinNamespaces(controllerName, nsDefaults); 3
    if (match != null) {
        return match;
    }

    
    return GetControllerTypeWithinNamespaces(controllerName, null /* namespaces */); 4
}

GetControllerType, first searches 1 the route namesapaces for the matching controller type. It will exit the search if a match is found or the namespace fallback option 2 is set to false. If the previous two conditions were not satisfied the function will search for the type in the application's default namespaces collection 3. This is the scenario explained at the beginning of this post. Finally there will be a fallback option to search all of the namespaces for valid controller type. 4

Asp.net MVC Areas in depth

2009-10-04T12:10:05.617

protected void Application_Start()
{
     AreaRegistration.RegisterAllAreas(); 1
     RegisterRoutes(RouteTable.Routes);
}

In the Application_Start event, the Asp.net MVC application registers the areas by calling a static function on the AreaRegistration abstract class 1.

public static void RegisterAllAreas() 
{
      RegisterAllAreas(null);
}

public static void RegisterAllAreas(object state) 
{
                                 2                        3
      RegisterAllAreas(RouteTable.Routes, new BuildManagerWrapper(), state);
}

RegisterAllAreas function was finally invoked with a RouteCollection 2 and an IBuildManager instance 3.

Buildmanager provides the methods to manage the Asp.net compilation. GetReferencedAssemblies method of the Buildmanager will return a collection of assemblies which includes those specified in assemblies element of web.config, assemblies built from App_Code folder, and assemblies from other top level folders.

internal static void RegisterAllAreas(RouteCollection routes, IBuildManager buildManager, object state) 
{
                                                                                               4
        List areaRegistrationTypes = TypeHelpers.FilterTypesInAssemblies(buildManager, IsAreaRegistrationType);
        foreach (Type areaRegistrationType in areaRegistrationTypes) 
        {
            AreaRegistration registration = (AreaRegistration)Activator.CreateInstance(areaRegistrationType);5
            registration.CreateContextAndRegister(routes, state);
        }
}

From the referenced assemblies, the application filters, using a predicate 4, those of AreaRegistration Type and creates an instance for each item found 5. In asp.net MVC preview 2 a class that is derived from AreaRegistration Type should be present in the corresponding area's folder and the instances of these classes are the ones created in the above step.

public class Routes: AreaRegistration 6
{
                                           7
    public override void RegisterArea(AreaRegistrationContext context)
    {
        context.MapRoute("blog_default", "Blog/{controller}/{action}/{id}",
                             new {controller = "Post", action = "index", id = ""});8
    }

    public override string AreaName 5
    {
        get { return "blog"; }
    }
}

CreateContextAndRegister method of AreaRegistration instance packages the RouteCollection, object state, and area name 5 (which is obtained from the user defined AreaRegistration derived class 6) in to an AreaRegistrationContext and passes the context 7 to the RegisterArea method which is implemented in the user defined AreaRegistration class. The custom defined AreaRegistration class then can add the required routes 8 to the RoutesCollection and the internals of these will be further explored in the next post.

Sequential Workflow - Part 2

2009-09-28T11:29:29.82

partial class ATMSimulator
{
      #region Designer generated code

      ///  
      /// Required method for Designer support - do not modify 
      /// the contents of this method with the code editor.
      /// 
      [System.Diagnostics.DebuggerNonUserCode]
      private void InitializeComponent()
      {
          this.CanModifyActivities = true;
          System.Workflow.Activities.CodeCondition codecondition1 = new System.Workflow.Activities.CodeCondition();
          this.DispatchAmount = new System.Workflow.Activities.CodeActivity();
          this.GatherAmountInput = new System.Workflow.Activities.CodeActivity();
          this.CashWithdrawalSequence = new System.Workflow.Activities.SequenceActivity();
          this.WhileUserNeedsATMService = new System.Workflow.Activities.WhileActivity();
          // 
          // DispatchAmount
          // 
          this.DispatchAmount.Name = "DispatchAmount";
          this.DispatchAmount.ExecuteCode += new System.EventHandler(this.DispatchAmount_ExecuteCode);
          // 
          // GatherAmountInput
          // 
          this.GatherAmountInput.Name = "GatherAmountInput";
          this.GatherAmountInput.ExecuteCode += new System.EventHandler(this.GatherAmountInput_ExecuteCode);
          // 
          // CashWithdrawalSequence
          // 
          this.CashWithdrawalSequence.Activities.Add(this.GatherAmountInput); 3
          this.CashWithdrawalSequence.Activities.Add(this.DispatchAmount);
          this.CashWithdrawalSequence.Name = "CashWithdrawalSequence";
          // 
          // WhileUserNeedsATMService
          // 
          this.WhileUserNeedsATMService.Activities.Add(this.CashWithdrawalSequence);2
          codecondition1.Condition += new System.EventHandler  ( his.CheckUserNeedsATMService);
          this.WhileUserNeedsATMService.Condition = codecondition1; 4
          this.WhileUserNeedsATMService.Name = "WhileUserNeedsATMService";
          // 
          // ATMSimulator
          // 
          this.Activities.Add(this.WhileUserNeedsATMService);
          this.Name = "ATMSimulator";
          this.CanModifyActivities = false;

      }

      #endregion

      private CodeActivity DispatchAmount;
      private SequenceActivity CashWithdrawalSequence;
      private WhileActivity WhileUserNeedsATMService; 1
      private CodeActivity GatherAmountInput;

}

The major differnce from the Part 1 in this workflow is the inclusion of WhileActivity 1 so that the user can make more than one transaction in one go. WhileActivity is a CompositeActivity so it can conatin other activities 2. Since WhileActivity can execute only single activity, the previous activities are packaged in to a single SequenceActivity 3 and given to the WhileActivity 2. The Condition property of WhileActivity, which is set to an instance of CodeCondition 4 in this code, determines whether the WhileActivity should proceed or halt.

public sealed partial class ATMSimulator : SequentialWorkflowActivity
{
      private int amountToWithdraw = 0;
      private bool userNeedsService = true;

      public ATMSimulator()
      {
          InitializeComponent();
      }
      private void GatherAmountInput_ExecuteCode(object sender, EventArgs e) 1
      {
          Console.WriteLine("please sepecify the amount to withdraw");
          amountToWithdraw = int.Parse(Console.ReadLine());
      }

      private void DispatchAmount_ExecuteCode(object sender, EventArgs e) 2
      {
          Console.WriteLine(String.Format("Please collect {0:c} from the ATM", amountToWithdraw));
          Console.WriteLine("Enter Q to quit");
          userNeedsService = !Console.ReadLine().Equals("Q", StringComparison.OrdinalIgnoreCase); 3
       }

      private void CheckUserNeedsATMService(object sender, ConditionalEventArgs e) 4
      {
          e.Result = userNeedsService; 5
      }


}

The sequence activities are executed 1 2 in the first go and sets whether the user needs to do further transactions 3. Based on the user's preference, CodeCondition event handler 4 sets the Result to a boolean value to signal whether the while loop should halt or proceed 5.

Sequential Workflow - Part 1

2009-09-28T12:32:21.18

public sealed partial class ATMSimulator : SequentialWorkflowActivity 1
{
      private int amountToWithdraw = 0;
      public ATMSimulator()
      {
          InitializeComponent();
      }

      private void GatherAmountInput_ExecuteCode(object sender, EventArgs e)2
      {
          Console.WriteLine("please sepecify the amount to withdraw");
          amountToWithdraw = int.Parse(Console.ReadLine());
      }

      private void DispatchAmount_ExecuteCode(object sender, EventArgs e)3
      {
          Console.WriteLine(String.Format("Please collect {0:c} from the ATM", amountToWithdraw));
      }

}

Activities are the primary building blocks in Windows Workflow Foundation (WF) and the sequential workflow itself is an activity called SequentialWorkflowActivity 1. As the SequentialWorkflowActivity inherits from the CompositeActivity, it can execute the code in the child activities 2 3 in a forward-only direction.

partial class ATMSimulator
{
      #region Designer generated code

      ///  
      /// Required method for Designer support - do not modify 
      /// the contents of this method with the code editor.
      /// 
      [System.Diagnostics.DebuggerNonUserCode]
      private void InitializeComponent()
      {
          this.CanModifyActivities = true;
          this.DispatchAmount = new System.Workflow.Activities.CodeActivity();
          this.GatherAmountInput = new System.Workflow.Activities.CodeActivity();
          // 
          // DispatchAmount
          // 
          this.DispatchAmount.Name = "DispatchAmount";
          this.DispatchAmount.ExecuteCode += new System.EventHandler(this.DispatchAmount_ExecuteCode);
          // 
          // GatherAmountInput
          // 
          this.GatherAmountInput.Name = "GatherAmountInput";
          this.GatherAmountInput.ExecuteCode += new System.EventHandler(this.GatherAmountInput_ExecuteCode);
          // 
          // ATMSimulator
          // 
          this.Activities.Add(this.GatherAmountInput);
          this.Activities.Add(this.DispatchAmount);
          this.Name = "ATMSimulator";
          this.CanModifyActivities = false;

      }

      #endregion

      private CodeActivity DispatchAmount; 4
      private CodeActivity GatherAmountInput; 5

}

In the designer generated file of the simulator program there exists two code activities 4 5. The primary goal of the code activities are to invoke the code-beside methods 2 3. These methods will be used to examine and change the workflow instance states.

EntityConnection code walkthrough

2009-09-27T10:57:21.487

// Specify the provider name, server and database.
string providerName = "System.Data.SqlClient";
string serverName = ".";
string databaseName = "AdventureWorks";

// Initialize the connection string builder for the
// underlying provider.
SqlConnectionStringBuilder sqlBuilder =
    new SqlConnectionStringBuilder(); 1

// Set the properties for the data source.
sqlBuilder.DataSource = serverName;
sqlBuilder.InitialCatalog = databaseName;
sqlBuilder.IntegratedSecurity = true;

// Build the SqlConnection connection string.
string providerString = sqlBuilder.ToString();2

SqlConnectionStringBuilder class 1 is used to create the Sql Server specific connection string 2. Later this generated connection string will be passed to the EntityConnectionStringBuilder instance. This gives the following advantages

Strongly typed connection string properties
Support for synonyms
Security

// Initialize the EntityConnectionStringBuilder.
EntityConnectionStringBuilder entityBuilder =
    new EntityConnectionStringBuilder();

//Set the provider name.
entityBuilder.Provider = providerName;3

// Set the provider-specific connection string.
entityBuilder.ProviderConnectionString = providerString;

// Set the Metadata location.
entityBuilder.Metadata = @"res://*/AdventureWorksModel.csdl|
                            res://*/AdventureWorksModel.ssdl|
                            res://*/AdventureWorksModel.msl";4
Console.WriteLine(entityBuilder.ToString());

Unlike the SqlConnectionStringBuilder, EntityConnectionStringBuilder is vendor agnostic and hence we need to specify the provider name 3 before generating the Entity connection string. Metadata file locations 4 should also be specified before constructing the connection string.

using (EntityConnection conn =
    new EntityConnection(entityBuilder.ToString()))
{
    conn.Open();
    Console.WriteLine("Just testing the connection.");
    conn.Close();
}