Windows Communication Foundation

ADO.NET Data Services: deleting entities with associations

alessandro.delsole@nospamvisual-basic.it — Sat, 11 Apr 2009 11:04:00 GMT

Probably this topic is more generally related to the ADO.NET Entity Framework programming, but in my case this was an issue I was experiencing with the ADO.NET Data Services, exposing an entity data model (I recorded some videos about).

Imagine you have a client application that sends a DELETE Http requests to a Data Service for deleting entities on the database. It's not unusual that your entity will have associations with other entities and so on. The "delete" action gets performed on the Entity Data Model, because this is just a .NET representation of the data source, but you'll probably get errors when trying to invoke the DataService.SaveChanges method, because the engine will try to delete a record from the database, which has associations. So, it would be necessary also to remove associated records. A work-around to accomplish this is setting the Delete action from within SQL Server Management Studio for a particular foreign key.

Supposing we're working on the Northwind database and our goal is being able of removing Orders with Order_Details associated, we can open the database and navigate to the foreign key called FK_Order_Details_Orders under the Order_Details table, as shown in the following picture:

Click the Modify command, and you'll be able to see the Foreign Key Relationships window. Here you can change the Delete rule to Cascade, as shown in the following picture:

In this way, deleting and Order entity will allow removing associated Order_Details. Another best practice in deleting entities is enforcing FK associations and regarding this Beth Massi wrote a great blog post which you can find here.

Alessandro

Creating and consuming WCF services with VS 2008 Express Editions - part two

Alessandro Del Sole (English) — Fri, 02 Jan 2009 18:43:00 GMT

In my previous post we saw how to utilize Microsoft Visual Studio 2008 Express Editions to create and consume Windows Communication Foundation services: Visual Web Developer 2008 for the first task and Visual Basic 2008 for the second one, observing how VWD does all the "dirty" work to publish the service to Internet Information Services.

In this post we want to use exclusively Visual Basic 2008 Express, reconstructing from zero the project. After starting VB 2008 Express, the first step to cover is creating a Class Library project that we'll call WcfExpressTemplate.

Once ready, to the project must be added two assembly references: System.ServiceModel.dll (the WCF assembly) and System.Runtime.Serialization.dll. Once we've done this, we have to write the contract, the interface that characterizes the service. We can also reuse the code file we created last time with VWD or add a new file called IExpressService.vb whose code is the following:

<ServiceContract()> _

Public Interface IExpressService

<OperationContract()> _

Function ValidateMailAddress(ByVal mailAddress As String) As Boolean

End Interface

The class that implements the contract is defined inside a file called ExpressService.svc.vb (we can reuse the previous from VWD) whose code is always this:

Public Class ExpressService

Implements IExpressService

Public Function ValidateMailAddress(ByVal mailAddress As String) As Boolean Implements IExpressService.ValidateMailAddress

Dim validateMail As String = "^([\w-\.]+)@((\[[0-9]{1,3}\.[0-9]{1,3}\.)|(([\w-]+\.)+))([a-zA-z]{2,4}|[0-9]{1,3})(\]?)$"

Return Regex.IsMatch(mailAddress, validateMail)

End Function

End Class

To complete this file, we need the .svc file that identifies the services via markup code. To add a .svc file to the project we call the Project|Add new item command but we need to use the text file template, because VB Express doesn't offer a .svc file template. As we said before, the file will be called ExpressService.svc and will contain the following markup:

<%@ ServiceHost Language="VB" Debug="true" Service="WcfServiceTemplate.ExpressService" CodeBehind="ExpressService.svc.vb" %>

The last step needed to create our service is adding a configuration file. For the same reasons we discussed about the .svc file, we need to add it using the Text file template. So let's add a Web.config file. Here we have a simplified code, because we're not in a Web application but in a class library, so some sections are not necessary:

<?xml version="1.0" encoding="utf-8" ?>

<system.serviceModel>

<service

name="WcfServiceTemplate.ExpressService"

behaviorConfiguration="MyServiceBehavior">

<endpoint address=""

binding="wsHttpBinding"

contract="WcfServiceTemplate.IExpressService" />

</service>

</services>

</behavior>

</serviceBehaviors>

</behaviors>

</system.serviceModel>

</configuration>

Substantially we specified just the ServiceModel section, that is the one related to the WCF service. Select Build|Build... to compile the project and verify that no exceptions are thrown. Our project is so cool that we want to transform it into a reusable project template for WCF each time we start Visual Basic 2008 Express, so we decide to export the project to a template. From the File menu, select the command Export template. The following two pictures show the two Wizard steps needed to export the project, underlining the template type (project template) and the various identifier to assign.

Don't you believe it's troue? J Try to create a new project and you'll see the new template among the available ones:

Now we have to face the most complex step, publishing the service to Internet Information Services. We need a temporary folder, in my pc I created one called C:\Temporary\ExpressSvc. In the mentioned ExpressSvc folder we must copy the Web.config and ExpressService.svc. Inside the folder we need then to create another subfolder called Bin, where we'll copy the WcfExpressTemplate.dll, which is effectively the WCF service.

Once done this, let's start Internet Information Services Manager from Windows' Administrative tools. Expand the tree structure until you see the default web site, right click it and select the Add Application command as shown here:

In the next window, let's specify the path where we manually deployed the service by assigning an Alias as shown here:

Now we can verify that the service has been correctly hosted typing the service URL in the addresses bar. Our browser will appear as follows:

This means that everything is working fine! Now we can reference our service from whatever .NET application. The following picture shows the Add Service Reference dialog, underlining how the service's metadata are reached and shown correctly:

And that’s all! J Perhaps a long series of steps, but I hope that it can be useful to clarify any doubts about creating and consuming WCF services with Visual Studio 2008 Express Edition.

Alessandro

Creating and consuming WCF services with VS 2008 Express Editions - part one

Alessandro Del Sole (English) — Fri, 02 Jan 2009 18:18:00 GMT

A question that I've often read inside the Visual Basic Tips & Tricks community forums is: "how do I create and consume WCF services if I have only Visual Studio 2008 Express Editions?". So in this post and in the next one we'll see right how to accomplish this. In this first post we'll see how to use Microsoft Visual Web Developer 2008 Express Edition to create a WCF service and Visual Basic 2008 Express Edition to consume the service, while in the next post we'll see how to use just Visual Basic 2008 to reconstruct the WCF service, publish to IIS and, consume it and export our code to a reusable project template.

Therefore, the first thing to do is starting Microsoft Visual Web Developer 2008 Express Edition (administrative privileges are required for subsquently publishing to IIS). Our purpose is creating a project about a WCF Service Application (so, not a Web site), using the template and assigning the project name as shown in the following picture:

After a few seconds, VWD 2008 is ready and the new project appears as follows:

Notice how, in Solution Explorer, there is the interface IService1.vb (the Contract), the configuration file and the service file (Service1.svc). As you probably know, in Visual Studio 2008 each .svc file has a code-behind file, that effectively implements the contract and that will be called Service1.svc.vb. When you double click the .svc file, by default Visual Studio opens the code-behind file and not the markup one. Ok, we're ready to create a quite useful example, even if quite simple. Our service will expose a method capable to validate e-mail addresses, via regular expressions. So, Solution Explorer rename the IService1.vb file in IExpressService.vb. Completely remove the default VB code and type the following:

<ServiceContract()> _

Public Interface IExpressService

<OperationContract()> _

Function ValidateMailAddress(ByVal mailAddress As String) As Boolean

End Interface

Now rename Service1.vb in ExpressService.vb and remove all the code added by default by Visual Web Developer. The class will implement the contract as follows:

Public Class ExpressService

Implements IExpressService

Public Function ValidateMailAddress(ByVal mailAddress As String) As Boolean Implements IExpressService.ValidateMailAddress

Dim validateMail As String = "^([\w-\.]+)@((\[[0-9]{1,3}\.[0-9]{1,3}\.)|(([\w-]+\.)+))([a-zA-z]{2,4}|[0-9]{1,3})(\]?)$"

Return Regex.IsMatch(mailAddress, validateMail)

End Function

End Class

The ValidateMailAddress method will verify that the email address received as an argument is a valid mail address, returning True or False according to the check result. Now we must update the references to interface and class inside Web.config. First, localize the System.ServiceModel section, then modify the service attributes as follows, specifying our interface and class identifiers:

The last step consists in updating the markup in the service file ExpressService.svc. In Solution Explorer, right click this file and from the popup menu select View Markup. The code must be updated as follows:

<%@ ServiceHost Language="VB" Debug="true" Service="WcfExpressService.ExpressService" CodeBehind="ExpressService.svc.vb" %>

Now we're ready to compile the code and build the service. From the Build menu, select the Build command (is followed by the project name) accepting modifies to Web.config related to debugging.

When ready, the service must be hosted by an host application. A typical scenario is hosting services in Internet Information Services and Visual Web Developer 2008 gets the hands dirty for us (this didn't happen in VS 2005). From the Build menu let's click Publish. You'll see a window where you can specify the publish path, that can be IIS, a local folder or an FTP server. You can also click the Browse ("...") button to select the desired path or writing by yourself. Let's type the path for publishing as shown in the following picture, accepting the default settings:

Once VWD has finished publishing without errors, let's verify that our service has been hosted correctly. Let's start our Web browser and type the service URL. If everything works fine, the browser should appear as follows:

At this point the service is ready to be consumed. Let's start Microsoft Visual Basic 2008 Express Edition and create a new Console application as an example. We need to add a service reference, by utilizing the Project|Add Service Reference command. Now, when the Add Service Reference dialog appears, we just need to type the service URL and click Go, as shown here:

As you can see, Visual Basic will list service's metadata and this means that the service has been reached correctly. Change the namespace identifier as shown in the above picture, then click OK.

Now we have anything we need to consume the service. For example, the following (simple) code waits for the user to enter an email address, verifies that it's a valid address and then shows a message:

Imports ConsoleApplication1.ExpressServiceReference

Module Module1

Sub Main()

'Client instance

Dim client As New ExpressServiceClient

'An e-mail address must be entered

Console.WriteLine("Type the mail address to validate:")

Dim mailAddress As String = Console.ReadLine

'Address validation via our WCF Service

If client.ValidateMailAddress(mailAddress) = True Then

Console.WriteLine("You entered a valid mail address")

Else

Console.WriteLine("The mail address you entered is invalid.")

End If

Console.ReadLine()

End Sub

End Module

We can normally instantiate the service and call the method as from a typical class. If we try to run the application, we'll obtain a similar result:

As you can see, creating and consuming WCF Services with Microsoft Visual Studio 2008 Express Editions is a really simple task. In the next post we'll see how to reproduce the work with the only Visual Basic 2008.

Alessandro