The Problem Solver : Data Access

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

Paging with the Silverlight RIA services DomainDataSource

Maurice — Mon, 27 Apr 2009 08:57:46 GMT

Using the declarative DomainDataSource that is part of the upcoming Silverlight 3 RIA services makes it quite easy to work with data. All you need to do is add a DomainDataSource control to the the XAML, point it to the generated DomainContext class (in this case NorthwindContext) and tell it which method to use to load the data from the web service(in this case LoadCustomers). Next add a DataGrid to display the data and you are good to go.

     <UserControl xmlns:dataControls="clr-namespace:System.Windows.Controls;assembly=System.Windows.Controls.Data.DataForm"  x:Class="LOBUsingRIAServices.CustomerListPage"

                 xmlns:data="clr-namespace:System.Windows.Controls;assembly=System.Windows.Controls.Data"  

                 xmlns:riaControls="clr-namespace:System.Windows.Controls;assembly=System.Windows.Ria.Controls"

                 xmlns:web="clr-namespace:LOBUsingRIAServices.Web"

                 xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 

                 xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">

        <Grid x:Name="LayoutRoot" Background="White">

            <riaControls:DomainDataSource x:Name="CustomerDataSource"

                                          LoadMethodName="LoadCustomers">

                <riaControls:DomainDataSource.DomainContext>

                    <web:NorthwindContext />

                </riaControls:DomainDataSource.DomainContext>

            </riaControls:DomainDataSource>

            <data:DataGrid ItemsSource="{Binding Data, ElementName=CustomerDataSource}" />

        </Grid>

    </UserControl>

Pretty simple and that is the way I like it

Adding paging.

Sometimes the lost of data to load can get somewhat large and you might not want to load all data. In that case all you need to do is add a PageSize and the DomainDataSource will only load enough data to display on a single page. You can do this by just setting the PageSize on the DomainDataSource but as we also need a control to allow the user to page trough the data it is easier to also add the DataPager control. Now you have the option of setting the PageSize on the DomainDataSource or the DataPager. I found that setting it on either would work just was well except for the initial load where the DataPager shows page 0 when the PageSize is set on the DomainDataSource while it is set to 1, the correct value, when set on the DataPager. I assume this is just a small bug in the current preview.

Another thing you can specify is the LoadSize. This determines how many rows are loaded with each request and if not set equals the PageSize. Setting this to double the PageSize will improve the responsiveness of the the client application so might be a good idea if the data isn’t too large.

    <UserControl xmlns:dataControls="clr-namespace:System.Windows.Controls;assembly=System.Windows.Controls.Data.DataForm"  x:Class="LOBUsingRIAServices.CustomerListPage"

                 xmlns:data="clr-namespace:System.Windows.Controls;assembly=System.Windows.Controls.Data"  

                 xmlns:riaControls="clr-namespace:System.Windows.Controls;assembly=System.Windows.Ria.Controls"

                 xmlns:web="clr-namespace:LOBUsingRIAServices.Web"

                 xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 

                 xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">

        <Grid x:Name="LayoutRoot" Background="White">

            <riaControls:DomainDataSource x:Name="CustomerDataSource"

                                          LoadMethodName="LoadCustomers"

                                          LoadSize="40">

                <riaControls:DomainDataSource.DomainContext>

                    <web:NorthwindContext />

                </riaControls:DomainDataSource.DomainContext>

            </riaControls:DomainDataSource>

            <data:DataGrid ItemsSource="{Binding Data, ElementName=CustomerDataSource}" />

            <dataControls:DataPager Source="{Binding Data, ElementName=CustomerDataSource}" 

                                    PageSize="20" />

        </Grid>

    </UserControl>

The DataPager control is quite easy to use as well. Just drop it below the DataGrid and point it to the DomainDataSource to use and it just works. One problem I ran into was adding the DataPager above the DataGrid though. When I did that the DataPager didn’t show up on the UI so the user could not page through the data even though it still limited the data to the first page.

Using progressive loading

Another nice option is delayed loading. When using progressive loading all you need to do is specify the LoadSize on the DomainDataSource. The DomainDataSource will now load the specified number of rows, wait a bit and load the next set of rows. It will keep on doing this until all data is loaded. The nice thing here is that all the data is loaded but the UI still stays responsive for the user. De the default interval between load requests is 0.75 seconds but this can be fine tuned using the LoadDelay time span on the DomainDataSource.

    <UserControl xmlns:dataControls="clr-namespace:System.Windows.Controls;assembly=System.Windows.Controls.Data.DataForm"  x:Class="LOBUsingRIAServices.CustomerListPage"

                 xmlns:data="clr-namespace:System.Windows.Controls;assembly=System.Windows.Controls.Data"  

                 xmlns:riaControls="clr-namespace:System.Windows.Controls;assembly=System.Windows.Ria.Controls"

                 xmlns:web="clr-namespace:LOBUsingRIAServices.Web"

                 xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 

                 xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">

        <Grid x:Name="LayoutRoot" Background="White">

            <riaControls:DomainDataSource x:Name="CustomerDataSource"

                                          LoadMethodName="LoadCustomers"

                                          LoadSize="10"

                                          LoadDelay="0:0:0.25">

                <riaControls:DomainDataSource.DomainContext>

                    <web:NorthwindContext />

                </riaControls:DomainDataSource.DomainContext>

            </riaControls:DomainDataSource>

            <data:DataGrid ItemsSource="{Binding Data, ElementName=CustomerDataSource}" />

        </Grid>

    </UserControl>

And all of this was done without writing any code add everything was completely declarative. Of course it is just a matter of setting properties so doing so from code is easy enough.

Enjoy!

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!