The Problem Solver : LINQ

Nederlandse CodeCamp 2009

Maurice — Mon, 19 Oct 2009 10:26:00 GMT

Op 21 november 2009 organiseren de SDN, Stichting dotNed en VBcentral samen het derde Nederlandse Code Camp. Dit is een dag lang met code, code sharing, freaking en gezellig samenzijn. Een evenement door ontwikkelaars, voor ontwikkelaars. De regie ligt voor een belangrijk deel bij de deelnemers! Het aantal plaatsen voor deelnemers is wel beperkt tot maximaal 150. Wacht dus niet te lang met beslissen want voor je het weet is er geen plaats meer. Vergeet bij je aanmelding niet op te geven welke onderwerpen je interesse hebben. Bovendien nodigen we iedereen graag uit om zelf een sessie in te vullen.

Op de website, www.codecamp.nl, vind je meer informatie en kan je je aanmelden.

Combined DevelopMentor instructors blog feed.

Maurice — Wed, 19 Aug 2009 07:37:12 GMT

Michael Kennedy, one of the co instructors from DevelopMentor, has created a combined feed from all the blogs of the various DevelopMentor. An awesome group of people with a lot of knowledge to share. Highly recommended in you RSS reader.

http://feeds.feedburner.com/DevelopmentorInstructors

If you want to check out a list of the individual blog feeds look here.

Enjoy!

www.TheProblemSolver.nl
Wiki.WindowsWorkflowFoundation.eu

Want to download all MIX sessions?

Maurice — Tue, 31 Mar 2009 06:52:40 GMT

Then you should check Mike Swanson’s blog post here. He has two batch files, the first downloads all MIX session recordings with in the format you like, the second renames them so it is easier to make sense of all the media file names.

If you just want a list of all sessions with download links this page might be the thing for you.

So much better than downloading them by hand. Not as good as going to the MIX itself but if you, like me, couldn’t go it is still a nice way to see all the content.

Enjoy!

Software Development Event march 30th

Maurice — Mon, 23 Mar 2009 15:40:29 GMT

Just one week to go to the next Software Development Event. The schedule with all the sessions is looking good. But this time there is even more!

We will have a Microsoft Surface machine somewhere in the common area for people to try our. And if you have never played, oops tested, with a Surface machine before this is a truly exiting machine!

Just goes to show, the SDN will go to extraordinary efforts to please all attendees

You can see the full schedule here. And don’t forget, we are not in Ede this time but in a great new location in Driebergen.

Hope to see everyone there next week Monday.

www.TheProblemSolver.nl
Wiki.WindowsWorkflowFoundation.eu

And now on Twitter at http://twitter.com/mauricedb.

Looking back at the MVP Summit

Maurice — Sat, 07 Mar 2009 11:08:09 GMT

Last week lots of MVP, myself included, where in Redmond visiting Microsoft on our yearly MVP pilgrimage. The MVP Summit is always a great event. Not only do we get to talk to the MS team members who actually design and build all the software we love and use but we also get to meet each other. And with MVP’s being located around the world that is kind of rare as well.

Despite this being a great event I still have very mixed feelings about this last MVP summit. The problem isn’t the events itself or the people I met, that was al great . No the problem was in some of the technological decisions made in product groups. Unfortunately I can’t divulge details yet because I have signed an NDA but as soon .NET 4.0 as beta 1 is made public I will be able to blog about some of these decisions. And rest assured I will!

The reason we really need to is the way these important changes are communicated. Or should I say not communicated. Some very important changes where not communicated at all and could only be derived by bullet points missing from PowerPoint slides. Only when directly asked about the missing bullet point would someone say “Yes that is right, we decided to …. NDA … because … NDA …”. Sorry about the NDA part .

I can only say that these decisions are a big problem and I know several MVP’s who decided to skip other sessions on the same product as a result. I didn’t, as far as I am concerned ignoring a problem is not going to make it go away, but I really think this product team needs to reevaluate this decision and the general future trend.

Despite this hiccup I am very exited about lots of the things I got to see and am really looking forward to .NET 4 and Visual Studio 2010. Now if we only could have a beta today . When we will have a first beta is still a big question though. If a date was announced I missed it, the best I heard was a quarter and is quite a time span.

Enjoy.

www.TheProblemSolver.nl
Wiki.WindowsWorkflowFoundation.eu

Consuming an ADO.NET Data Service from Silverlight

Maurice — Tue, 06 Jan 2009 12:02:05 GMT

When developing Silverlight line of business (LOB) applications we often need to get at some data from a database. There are various ways to do so. One option that is easy to get started with with is creating an ADO.NET Entity Data Model (EDM) and exposing that entity model using an ADO.NET Data Service.

Getting started

The first thing we need to create is an ASP.NET Web Application. This is basically going to act as a container for our Data Service and our Silverlight LOB application. As you can see below I named the Web Application SLDataService.

Next we need to add the ADO.NET Entity Data Model. I already have a Northwind SQL Server database on my machine and that is the database I am going to expose to I am naming the EDM Northwind.edmx.

When the popup ask if I want to create a new EDM based on an existing database or start from scratch I selected the existing database option and pointed it at my Northwind database. This lets me select the tables I want to import. In this case I am only interested in the Customers table so that is what I am importing. By default the class name will be the same as the table name, i.e. Customers, but as Customer is a more logical name I removed the training “s”.

Next step is creating the ADO.NET Data Service to publish the entity model. Add another item to the project, this time choosing an ADO.NET Data Service and naming it Northwind.svc.

If we open the Northwind.svc.cs file we need to enter a few details before we can proceed. The first thing we need to enter is EDM class name we are going to expose. In this case that is the NorthwindEntities model. Next we need to allow callers to access the EDM. By default nothing is exposed to this is a crucial step that needs to be done in the InitializeService() function! In this case I am going to allow everything, maybe not the best solution in real live

public class Northwind : DataService<NorthwindEntities>
{
    public static void InitializeService(IDataServiceConfiguration config)
    {
        config.SetEntitySetAccessRule("*", EntitySetRights.All);
    }
}

Testing our data service

Now we should be able to test our ADO.NET Data Service in the browser. Start the project and you should see the following in the browser.

Navigate to the following URL http://localhost:4163/Northwind.svc/CustomerSet by adding CustomerSet and you should see the following customer data.

If you see an RSS feed instead of the XML go into settings and disable the feed reading view. BTW the reason the customers data is showing up as an RSS feed is because the ADO.NET Data Services uses the ATOM feed format to transmit its data using a REST approach.

Creating a Silverlight LOB client

The next step is to create a Silverlight client application to consume and display the data. Add a new project the solution of type Silverlight Application and name it SilverlightClient.

When prompted just accept the defaults and add the Silverlight application to the existing SLDataService app. Next we need to add a service reference to the Northwind ADO.NET Data Service. Call it NorthwindService.

Next we need to set up a bit of a user interface to display the list of customers. I kept this really simple and used a ListBox with a DataTemplate like this:

<UserControl x:Class="SilverlightClient.Page"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
    Width="500" Height="300">
    <Grid x:Name="LayoutRoot" Background="White">
        <ListBox x:Name="lstCustomers">
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <StackPanel Orientation="Horizontal">
                        <TextBlock Text="{Binding CompanyName}" Width="250" />
                        <TextBlock Text="{Binding City}" Width="100" />
                        <TextBlock Text="{Binding Country}" Width="100" />
                    </StackPanel>
                </DataTemplate>
            </ListBox.ItemTemplate>
        </ListBox>
    </Grid>
</UserControl>

The final step is to load the data from the service and bind this to the ListBox. To do that we need to create an DataServiceContext object of type NorthwindEntities. Unlike a regular service reference the DataServiceContext does not know its own URL by default and we need to be given the URL where the web service is located. Easy enough using the URL of the current page, loaded using HtmlPage.Document.DocumentUri, and the name of the service, Northwind.svc in this case.

Uri uri = new Uri(HtmlPage.Document.DocumentUri, "Northwind.svc");
NorthwindEntities context = new NorthwindEntities(uri);

Using this context object we can do a LINQ query to load some data. Pretty standard stuff except that the asynchronous nature of Silverlight changes the actual loading of the data a bit. Normally you would expect to do something like:

var query = from cust in context.CustomerSet 
            select cust;

lstCustomers.ItemsSource = query.ToList();

In this case that won’t work and will only result in an System.NotSupportedException with the following message "Specified method is not supported.".

The correct way of doing this is by using a DataServiceQuery object which can load the data asynchronously as follows:

var query = from cust in context.CustomerSet 
            select cust;

var dsQuery = (DataServiceQuery<Customer>)query;
dsQuery.BeginExecute(
    result => lstCustomers.ItemsSource = dsQuery.EndExecute(result), 
    null);

And the final result looks like this

Not bad at all

The complete code behind looks like this:

using System;
using System.Data.Services.Client;
using System.Linq;
using System.Windows;
using System.Windows.Browser;
using System.Windows.Controls;
using SilverlightClient.NorthwindService;

namespace SilverlightClient
{
    public partial class Page : UserControl
    {
        public Page()
        {
            InitializeComponent();
            Loaded += new RoutedEventHandler(Page_Loaded);
        }

        void Page_Loaded(object sender, RoutedEventArgs e)
        {
            Uri uri = new Uri(HtmlPage.Document.DocumentUri, "Northwind.svc");
            NorthwindEntities context = new NorthwindEntities(uri);
 
            var query = from cust in context.CustomerSet 
                        select cust;

            // This doesn't work and will throw an System.NotSupportedException!
            // lstCustomers.ItemsSource = query.ToList();

            var dsQuery = (DataServiceQuery<Customer>)query;
            dsQuery.BeginExecute(
                result => lstCustomers.ItemsSource = dsQuery.EndExecute(result), 
                null);
        }
    }
}

Visual Studio project sampe code

Enjoy!

www.TheProblemSolver.nl
Wiki.WindowsWorkflowFoundation.eu

Updated SQL Server Compact Workflow Persistence Service

Maurice — Wed, 12 Nov 2008 13:46:12 GMT

Yesterday I uploaded a new version of the SQL Server Compact Workflow Persistence Service to code.msdn.com. No major changes this time just two new features to get it more in line with the standard SqlWorkflowPersistenceService.

I added a GetAllWorkflows() function that returns all persisted workflow's in the database.
I added a LoadExpiredTimerWorkflowIds() function that will return a list of workflow instanceId's of all workflow's with an expired timer.

Both new functions should help make the SqlCeWorkflowPersistenceService even more like the out of the box SqlWorkflowPersistenceService. And as before it is completely free .

You can download the source code for the SqlCeWorkflowPersistenceService here: http://code.msdn.microsoft.com/SqlCeWFPersistence.

PS should you need to develop a custom WorkflowPersistenceService for some other database this would be a good starting point!

Enjoy.

www.TheProblemSolver.nl
Wiki.WindowsWorkflowFoundation.eu

PDC session download

Maurice — Sat, 01 Nov 2008 10:17:52 GMT

Want to download and watch all PDC content? Then there are a couple of ways to get at them. The official way if to go through the session agenda at the conference site. See https://sessions.microsoftpdc.com/public/timeline.aspx. You see all sessions but it takes a bit of work. Another nice way is through Channel 9 by using the following feed: http://channel9.msdn.com/posts/pdc2008/RSS/?tag=videos.

But the best as far as I am concerned is using the list compiled by Greg Duncan. Check this list http://coolthingoftheday.blogspot.com/2008/10/pdc2008-quick-video-link-list.html. And it even has the Visual Basic source code used to generate the list

Enjoy the videos!

www.TheProblemSolver.nl
Wiki.WindowsWorkflowFoundation.eu

Red Gate to continue development of .NET Reflector

Maurice — Wed, 20 Aug 2008 07:04:54 GMT

.NET Reflector, by Lutz Roeder, must be one of the most useful tools I have when developing .NET code. Usually it is the first thing I install right after Visual Studio not even waiting until I need it because I know I will.

So the big news is that Red Gate, makers of the Ants profiler and lots of other tools, are taking over from Lutz Roeder and will continue developing .NET Reflector. Interesting move and I hope this means a bright future for the .NET Reflector.

.NET Framework 3.5 Enhancements Training Kit

Maurice — Tue, 19 Aug 2008 10:32:52 GMT

Want to know what is new in the .NET 3.5 SP1 framework or Visual Studio 2008 SP1? Then check out the presentations and labs here: http://www.microsoft.com/downloads/details.aspx?FamilyID=355C80E9-FDE0-4812-98B5-8A03F5874E96&displaylang=en

Overview

The .NET Framework 3.5 Enhancements Training Kit includes presentations, hands-on labs, demos, and event materials. This content is designed to help you learn how to utilize the .NET 3.5 Enhancement features including: ASP.NET MVC, ASP.NET Dynamic Data, ASP.NET AJAX History, ASP.NET Routing, ADO.NET Data Services, ADO.NET Entity Framework, WCF 3.5 SP1, and the .NET Framework Client Profile.

Now this is nowhere near complete but a good place to start.

Enjoy!

Visual Studio 2008 Service Pack 1 available

Maurice — Mon, 11 Aug 2008 15:33:33 GMT

It is available from the subscriptions download at http://msdn.microsoft.com/en-us/subscriptions/default.aspx

Get it while it is hot

Enjoy!

SQL Server Compact 3.5 SP1 released

Maurice — Thu, 07 Aug 2008 07:47:58 GMT

Steve Lasker just announced that SQL Server Compact 3.5 service pack 1 is released, read his announcement here.

They added support for the entity framework, great stuff. And another neat feature is native 64 bits support. No longer do you need to target X86 and use WoW [:0]. Great if you are using my SQL Server Compact Workflow Persistence Service.

Enjoy!

CodeCamp 2008

Maurice — Sat, 02 Aug 2008 08:39:22 GMT

Afgelopen jaar hebben we het eerste CodeCamp in Nederland georganiseerd en dat was een groot succes. De meeste deelnemers vroegen om meer, sommige zelfs om een CodeCamp per kwartaal of een heel weekend lang. Nou hebben we dat laatste nog niet gedaan maar we zijn wel aan de slag gegaan om een nieuw CodeCamp te organiseren. Als datum hebben we zaterdag 6 september gekozen. Gelukkig waren Microsoft en Class-a behulpzaam en kunnen we, net als vorig jaar, weer in het Microsoft Innovation Center in Barneveld terecht. Een mooie datum en locatie om uitgerust van de vakantie een hoop kennis uit te wisselen.

Het programma staat nog niet helemaal vast, hou daar de website voor in de gaten, maar je kan er ondermeer de bekende Nederlandse sprekers verwachten. Uiteraard kan je zelf ook nog een sessie voorstellen dus als je een idee hebt voor een leuke sessie laat het dan zo snel mogelijk weten.

Dus zet de datum vast in je agenda en meld je zo snel mogelijk aan op de website www.code-camp.nl.

Het CodeCamp is een gezamenlijk initiatief van de SDN, de stichting DotNed en VB Central.

Lambda expression simplify code

Maurice — Mon, 26 May 2008 08:54:39 GMT

One of the nice new features in Visual Basic 9 are lambda expressions. They where actually added as one of the underlying pieces for LINQ. But besides enabling LINQ you can use them in all sorts of places. One of the places they really help me is in places where I previously needed to declare a delegate and use that.

Take for example the following code where I use the ThreadPool to do some work:

Private Sub btnStart_Click() Handles btnStart.Click
    ThreadPool.QueueUserWorkItem(AddressOf DoWork)
End Sub

Private Sub DoWork(ByVal state As Object)

    For index As Integer = 1 To 100
        SetProgressLabel(index)
        Thread.Sleep(100)
    Next
End Sub

The SetProgressLabel function reports the progress to the user by setting the text on a label. As the work is done in a background thread I need to use Invoke to set the text property.

Before VB9 I would have to implement the SetProgressLabel like this:

Delegate Sub SetProgressLabelDelegate(ByVal percentage As Integer)
Private Sub SetProgressLabel(ByVal percentage As Integer)
    If lblStatus.InvokeRequired Then
        lblStatus.Invoke( _
            New SetProgressLabelDelegate( _
                AddressOf SetProgressLabel), _
                percentage)
    Else
        lblStatus.Text = percentage.ToString() + " %"
    End If
End Sub

First I would need to declare a delegate with the right signature, create an object passing in the address of the function to call and the parameters. Even though I declared the delegate with its parameters the Invoke is not aware of these and I can add make errors with the parameters which don't show until runtime.

So here is a better way to do this in VB9:

Private Function SetProgressLabel(ByVal percentage As Integer) As Object
    If lblStatus.InvokeRequired Then
        lblStatus.Invoke(Function() SetProgressLabel(percentage))
    Else
        lblStatus.Text = percentage.ToString() + " %"
    End If
    Return Nothing
End Function

This time I use an lambda expression to call the SetProgressLabel function. No need for the extra delegate and I get full compile time checking . In fact the only drawback is that I need to declare SetProgressLabel as a function instead of a sub as VB forces a lambda expression to return a value. This makes working with lambda expressions somewhat less powerful than the C# implementation Lets just hope that problem is rectified soon.

One neat thing is that you don't actually need to target the 3.5 framework to use lambda expressions. The previous sample works just fine targeting the .NET 2.0 runtime as long as VB9 is used. The reason for this is that the lambda expression syntax is actually just a compiler trick and it creates an delegate for us behind the scenes. Pretty cool!

Enjoy!

www.TheProblemSolver.nl
http://wiki.WindowsWorkflowFoundation.eu

SQL Server Compact and 64 bits

Maurice — Tue, 20 May 2008 10:32:18 GMT

The current version of SQL Server Compact has no support for 64 bits computing. While this may seem a problem if you want to deploy you application on a 64 bits version of Windows it really isn't most of the time. In fact if you change your assembly from the default AnyCPU to x86 compatible it will work just fine using Windows On Windows (WOW).

But even better there will soon be a native 64bits version of SQL Compact. This isn't in the beta version that is distibrited with Visual Studio 2008 SP1 beta but Steve Lasker promises it will be in the final version when that releases.

Another nice feature that will be added is support for LINQ to Entities. And that includes the designer support we now lack with LINQ to SQL.

More info about the change can be found in this blog post by Steve Lasker.

Enjoy!

www.TheProblemSolver.nl
http://wiki.WindowsWorkflowFoundation.eu

How to Download all of Visual Studio 2008 SP1

Maurice — Fri, 16 May 2008 09:05:00 GMT

VS2008 SP1 Beta is quite a package. By default the installation downloads the packages as needed and when needed. Now that is just fine if you only need to install a single machine. But when you need to install multiple, possibly virtual, machines like I have to it just wastes a lot of bandwidth and time . Fortunately there is a solution and it can be found here in the blog post by Heath Stewart.

Enjoy!

Workflow Persistence Service using SQL Server Compact

Maurice — Thu, 10 Apr 2008 18:11:29 GMT

As I mentioned previously I was working in a Workflow Persistence Service using SQL Server Compact as the back end store. Now this might not be the best persistence store to use in every application but it has a number of advantages.

One of the main advantages is ClickOnce deployment. In the case of the standard SqlWorkflowPersistenceService you need to have SQL Server installed and running and create the database, with a name of your choosing, using two scripts. Not a big problem but something that needs to be done first and is outside of the realm of what you would like to do with ClickOnce. Not so with SQL Server Compact. No with SqlCe you can just deploy a number of DLL's with your application and you are ready to go, so much easier and very ClickOnce compatible Add easy installation is just what you want when you are creating sample applications.

I actually did all the data access using LINQ to SQL which fully supports SqlCe as a client. It might appear not to as there is no designer support like with SQL Server itself but runtime it works just fine . using LINQ to SQL actually made the data access very easy and has an additional benefit, if you want to use the full SQL Server all you need to do is provide a different database connections string. One additional benefit of using LINQ to SQL was that is can check if the database exists and, if not, create it with a single function call. No need to mess with those tedious Create Table statements in SQL scripts!

Imports TheProblemSolver.Workflow.Hosting.Persistence

Module Module1
    Class Program
        Shared Sub Main()
            Using workflowRuntime As New WorkflowRuntime()

                Dim connectionStr As String = "Data Source=WorkflowPersistenceDatabase.sdf"
                Dim unloadOnIdle As Boolean = True
                Dim loadingInterval As TimeSpan = TimeSpan.FromSeconds(15)
                Dim persistence As New SqlCeWorkflowPersistenceService(connectionStr, _
                                                                       unloadOnIdle, _
                                                                       loadingInterval)
                workflowRuntime.AddService(persistence)

                Dim workflowInstance As WorkflowInstance
                workflowInstance = workflowRuntime.CreateWorkflow(GetType(Workflow1))
                workflowInstance.Start()

                Console.WriteLine("Press enter to stop...")
                Console.ReadLine()
            End Using
        End Sub
    End Class
End Module

Usage is real simple and pretty much the same as the standard SqlWorkflowPersistenceService type. The only extra is to set a reference to the TheProblemSolver.Workflow.Hosting.Persistence.dll that includes the SqlCeWorkflowPersistenceService type.

using System;
using System.Workflow.Runtime;
using TheProblemSolver.Workflow.Hosting.Persistence;

namespace TestClient
{
    class Program
    {
        static void Main(string[] args)
        {
            using (WorkflowRuntime workflowRuntime = new WorkflowRuntime())
            {
                string connectionStr = @"Data Source=WorkflowPersistenceDatabase.sdf";
                bool unloadOnIdle = true;
                TimeSpan loadingInterval = TimeSpan.FromSeconds(15);
                SqlCeWorkflowPersistenceService persistence = 
                    new SqlCeWorkflowPersistenceService(connectionStr, unloadOnIdle, loadingInterval);
                workflowRuntime.AddService(persistence);

                WorkflowInstance instance = workflowRuntime.CreateWorkflow(typeof(Workflow1));
                instance.Start();

                Console.WriteLine("Press enter to stop...");
                Console.ReadLine();
            }
        }
    }
}

If you want to download the SqlCeWorkflowPersistenceService you can find it here. Any feedback, hopefully good, will be appreciated!

Enjoy!

www.TheProblemSolver.nl
http://wiki.WindowsWorkflowFoundation.eu

LINQ to SQL, SQL Compact and the |DataDirectory| macro

Maurice — Wed, 09 Apr 2008 12:27:47 GMT

As I previously mentioned having the LINQ DataContext create the database if it doesn't exist yet is a cool feature but it isn't perfect.

The problem I just ran into was while using the |DataDirectory| macro, something the SqlCeConnection understands and will replace with the directory specified. Well it turns out the LINQ DataContext isn't that smart when checking if the database exists. Apparently it checks if the database file exists without expanding the |DataDirectory| so it never finds the database. The result is a SqlCeException with the message: "File already exists. Try using a different database name. [ File name = C:\Projects\ConsoleApplication1\ConsoleApplication1\bin\Debug\Data2.sdf ]"

Actually creating the database the first time works just fine and all other actions like querying or updating are fine to.

To reproduce the error create a console app and add a LINQ to SQL DBML file. Just add a small class with a property to server as table.

Add the following code:

Module Module1
    Sub Main()
        Try
            ' Cleanup any previous files
            My.Computer.FileSystem.DeleteFile("Data1.sdf")
            My.Computer.FileSystem.DeleteFile("Data2.sdf")
        Catch ex As Exception
        End Try

        For i As Integer = 1 To 2
            CreateDatabaseIfNeeded("Data Source=Data1.sdf")
            CreateDatabaseIfNeeded("Data Source=|DataDirectory|\Data2.sdf")
        Next
    End Sub

    Sub CreateDatabaseIfNeeded(ByVal connection As String)
        Dim context As New DataClasses1DataContext(connection)
        If Not context.DatabaseExists() Then
            Console.WriteLine("Creating database")
            context.CreateDatabase()
        Else
            Console.WriteLine("Database exists")
        End If
    End Sub
End Module

And run the application.

Want to see this fixed? The vote for it here.

Enjoy!

www.TheProblemSolver.nl
http://wiki.WindowsWorkflowFoundation.eu

LINQ to SQL and creating databases

Maurice — Wed, 09 Apr 2008 10:19:06 GMT

LINQ to SQL has a really nice feature when making sample and demos in the ability to create the database if it doesn't exist yet. It also has a function called DatabaseExists() to check if a database exists. Both are defined on the DataContext class.

string connectionString 
    = @"Data Source=.\sqlexpress;Initial Catalog=MyNewDatabase;Integrated Security=True";

MyNewDatabase context = new MyNewDatabase(connectionString);
if (!context.DatabaseExists())
    context.CreateDatabase();

And best of all they work both for SQL Server and for SQL Compact so it is real easy to make demo's that work with both the full SQL Server as well as the lightweight SQL Compact. All you need to do is change the connection string.

connectionString = @"Data Source=MyNewDatabase.sdf";

Now I specially like the SQL Compact option for samples as there is no installation requirement, just copy the files and you are good to go . In fact I have been using LINQ to SQL to create a SQL Compact Workflow persistence service but because of the very nature of LINQ to SQL I can use it just as well with the full blown SQL Server as SQL Compact.

So why do I consider the DatabaseExists() function only suitable for demo's? Well in the case of SQL Server it makes a connection to the server and sees if it can use the database. Hardly a very reliable check as it can fail for any number of reasons. And if the database exists it still doesn't mean that the schema is correct. For SQL Compact the check is even worse, it only checks if a file with the same name exists, no matter what it is.

Enjoy!

www.TheProblemSolver.nl
http://wiki.WindowsWorkflowFoundation.eu

On the WF ReceiveActivity and WCF bindings

Maurice — Wed, 26 Mar 2008 16:46:22 GMT

The new ReceiveActivity and SendActivity that marry Windows Workflow Foundation (WF) and Windows Communication Foundation (WCF) are really cool . Getting started is easy because a new Sequential Workflow Service Library, found under WCF instead of Workflow in VS2008, uses nice defaults for everything. But sooner or later you need to change these defaults and you need to know what can be done and what can't.

When you want to use the new ReceiveActivity in a workflow you need to use a compatible WCF binding. The reason for this requirement is that the conversation context, see this blog post, is part of the message and needs to be retrieved and returned. The following code returns a list of all WCF binding and how they are composed:

Sub Main()

Dim assemblies As New List(Of Assembly)()

' .NET 3.0

assemblies.Add(GetType(ServiceHost).Assembly)

' .NET 3.5

assemblies.Add(GetType(WorkflowServiceHost).Assembly)

assemblies.Add(GetType(WebServiceHost).Assembly)

Dim query = From assembly In assemblies _

From type In assembly.GetTypes() _

Where type.IsSubclassOf(GetType(Binding)) _

AndAlso Not type.IsAbstract _

AndAlso type.IsPublic _

Order By type.Name _

Select type

PrintBinding(query.ToList)

Console.ReadLine()

End Sub

Private Sub PrintBinding(ByVal types As List(Of Type))

For Each type In types

Console.WriteLine(type.FullName)

Try

Dim binding As Binding = _

CType(Activator.CreateInstance(type), Binding)

Dim elements = binding.CreateBindingElements

For Each element In elements

Console.WriteLine(vbTab + element.GetType().FullName)

Catch ex As Exception

Console.WriteLine(ex.Message)

End Try

Console.WriteLine()

End Sub

The classes responsible for inserting and removing these conversation tokens are ContextRequestChannel and ContextReplyChannel and they are instantiated by the ContextBindingElement. So seems we are restricted to using BasicHttpContextBinding, NetTcpContextBinding or WSHttpContextBinding.

So it seems we cannot use NetMsmqBinding which is a shame because one way reliable messaging is the perfect fit for workflow as far as I am concerned. Well not quite so fast because we still have the CustomBinding where we can configure the stack just the way we want right?

Yeah we do but there is a problem . It turns out the ContextBinding requires a channel with an IReplyChannel interface and the NetMsmqBinding actually implement an IInputChannel or an IOutputChannel. Which one actually depends if you are the client or the service.

And thinking about how WF/WCF conversations works this restriction makes sense. After all a ReceiveActivity is called without a context in order to create a new workflow, assuming the CanCreateInstance property equals true, and returns the workflow instanceId in the context as part of the response. This design kind of rules out one-way messages and thereby NetMsmqBinding.

Now this sucks big time if you ask me . I would much rather have seen that you could specify the instanceId of the workflow to be created, just as you can with the WorkflowRuntime.CreateWorkflow() where a number of the overloads let you specify the workflows instanceId. I suppose it is possible to create a different context binding but that would be quite some work and, I assume, duplicate a lot of code already written my Microsoft. So let's hope they see the light and add MSMQ/ReceiveActivity intergration.

Enjoy!

www.TheProblemSolver.nl
http://wiki.WindowsWorkflowFoundation.eu