Introduction into ADO .NET Data Services/RIA Services

I recently spent some time writing up a new article on using both

• ADO .NET Data Services
• RIA Services

If you have not messed around with these 2 data access technologies this new article may be of interest to you. I do not go into advanced scenarios, but I do cover the basic CRUD operations in both technologies.

I cover the following things

1. Creating Data
2. Retrieving Data
3. Updating Data
4. Deleting Data
5. Validation

So if you think you may find this useful, have a read of the following article.

http://www.codeproject.com/KB/silverlight/DataAndRIA.aspx

Lazy

I love it when I find a new .NET class that I have never used before. That just happened to me, I cam across a little class called Lazy<T>.

The idea behind Lazy<T> is that it is a simple wrapper for an object that may be expensive to create, maybe one that hits the database or something like that. And you do not want to create this object until you need to, that is what Lazy<T> is all about.

It is very simple to use, all you need to do is specify the type of T, and then you can examine the wrapped value to see if has been created yet using the Lazy<T>.IsValueCreated property. Simliarly if you want to get the actual T instance out, you just need to use the Value property.

Here is small example of setting it up and using it

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;

namespace Laziness
{
    class Program
    {
        static void Main(string[] args)
        {
            //Construction normally
            Lazy<SomeExpensiveClass> someExpensiveClass = 
                new Lazy<SomeExpensiveClass>();

            Console.WriteLine(String.Format(
                "someExpensiveClass has value yet {0}",
                someExpensiveClass.IsValueCreated));
            Console.WriteLine(String.Format(
                "someExpensiveClass.SomeProperty value {0}",
                ((SomeExpensiveClass)someExpensiveClass.Value).
            SomeProperty.ToString()));
            Console.WriteLine(String.Format(
                "someExpensiveClass has value {0}",
                someExpensiveClass.IsValueCreated));

        }


    }



    public class SomeExpensiveClass
    {
        public int SomeProperty { get; set; }

        public SomeExpensiveClass()
        {
            Console.WriteLine("SomeExpensiveClass constructed");
        }
    }
}

Which would show the following

You can also use a Func<T> to control how the object is created, here is an example of that

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;

namespace Laziness
{
    class Program
    {
        static void Main(string[] args)
        {

            //Construction up using a Func for more specific construction
            Lazy<SomeExpensiveClass> someExpensiveClass2 = 
        new Lazy<SomeExpensiveClass>
                (
                    ()=>
                    {
                        SomeExpensiveClass fobj = new SomeExpensiveClass() 
                        { 
                            SomeProperty = 100 
                        };
                        return fobj;
                    }
                );
            Console.WriteLine(String.Format(
                "someExpensiveClass2 has value yet {0}", 
                someExpensiveClass.IsValueCreated));
            Console.WriteLine(String.Format(
                "someExpensiveClass2s.SomeProperty value {0}",
                ((SomeExpensiveClass)someExpensiveClass2.Value).SomeProperty.ToString()));

            Console.WriteLine(String.Format(
                "someExpensiveClass2 has value yet {0}", 
                someExpensiveClass.IsValueCreated));


            Console.ReadLine();

        }

    }



    public class SomeExpensiveClass
    {
        public int SomeProperty { get; set; }

        public SomeExpensiveClass()
        {
            Console.WriteLine("SomeExpensiveClass constructed");
        }
    }
}

.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, “Courier New”, courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }

Which when run looks like this:

And you can also ensure thread safety, have a look at this snippet

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;

namespace Laziness
{
    class Program
    {
        static void Main(string[] args)
        {

            //Construction up using a Func for more specific construction
            Lazy<SomeExpensiveClass> someExpensiveClass3 = 
                new Lazy<SomeExpensiveClass>
                (
                    () =>
                    {
                        SomeExpensiveClass fobj = new SomeExpensiveClass() 
                            { 
                                SomeProperty = 100 
                            };
                        return fobj;
                    },
                    true //is threadsafe
                );
            Console.WriteLine("Starting threaded test");
            //The Lazy object ctor is called twice and published to 
            //all threads, and as it was thread safe they all get same value
            ThreadPool.QueueUserWorkItem(new WaitCallback(DoThread), 
                someExpensiveClass3);
            ThreadPool.QueueUserWorkItem(new WaitCallback(DoThread), 
                someExpensiveClass3);

            Console.ReadLine();

        }



        static void DoThread(object obj)
        {
            Lazy<SomeExpensiveClass> lazy = 
        (Lazy<SomeExpensiveClass>)obj;
            SomeExpensiveClass someExpensiveClass3 = 
        (SomeExpensiveClass)lazy.Value;
            someExpensiveClass3.SomeProperty++;
            Thread.Sleep(10);
            Console.WriteLine(String.Format(
                "someExpensiveClass3.SomeProperty value {0}",
                someExpensiveClass3.SomeProperty.ToString()));
        }


    }



    public class SomeExpensiveClass
    {
        public int SomeProperty { get; set; }

        public SomeExpensiveClass()
        {
            Console.WriteLine("SomeExpensiveClass constructed");
        }
    }
}

.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, “Courier New”, courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }

Which when run looks like this:

As always here is a small demo project : Small demo project

 

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font-size: small;
color: black;
font-family: consolas, “Courier New”, courier, monospace;
background-color: #ffffff;
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.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
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.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }

WPF : How To Create Your Own Threaded DataSourceProvider

It has been a while since I posted something, but you see I have been moving house and do not have any internet at the moment, so it has been quite problematic.

After much delay I finally bit the bullet and and bought myself a mobile broadband dongle which enables me to work on the move. Hooray.

Anyway in this post I am going to show you guys how to create your own DataSourceProviders for WPF. For those that know nothing about DataSourceProviders, they are a way of fetching data directly from XAML, and you may use a sub class of DataSourceProvider to do the fetching of certain user requested data based on certain parameters. Basically it all starts by inheriting from DataSourceProvider.

Now WPF already has some very useful DataSourceProviders, such as

ObjectDataProvider : Which allows you to call methods in a certain class to obtain values. This is highly configurable through method name, parameters etc etc

XmlDataProvider : Which allows you to obtain XML data from various XML sources, such as XML file, XML data islands etc etc

These 2 classes that come with the framework are great, but occassionally it is useful to know how to write your own DataSourceProvider.

And as luck would have it it is not that hard. It basically boils down to 3 steps

1. Inherit from DataSourceProvider
2. Override BeginQuery()
3. Make sure to call OnQueryFinished() at some point with the data fetched

And that is all there is to it really. I will now show you an example of what this may look like, where the example is very contrived I must say, but it does showcase how to create a simple DataSourceProvider. This example allows the user to specify (in XAML) the name of embedded resource TXT file to read out line by line, which is then exposed as the data from the subclassed DataSourceProvider. This data can then be used as the ItemSource for say a ListBox/ComboBox or something like that.

One extra thing it provides is the ability to support background loading, which it does by examining the IsAsync property (which can be set from XAML), and if that is set will do the fetch on a background worker item within the ThreadPool.

Anyway here is the code:

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Windows.Data;

using System.ComponentModel;

using System.IO;

using System.Reflection;

using System.Threading;

namespace TXTDataProvider

{

    /// <summary>

    /// Very simple DataSourceProvider that shows

    /// how to read from resource files, and demonstrates

    /// how to do it Asnychrounsly

    /// </summary>

    public class TXTDataSourceProvider : DataSourceProvider

    {

        #region Data

        private Boolean isAsync = false;

        private String fileName = String.Empty;

        #endregion

        #region Overrides

        /// <summary>

        /// Begins the query to get the data. This examines the

        /// IsAsync flag to determine if it needs to be threaded

        /// and run in the background or not

        /// </summary>

        protected override void BeginQuery()

        {

            if (IsAsync)

                ThreadPool.QueueUserWorkItem(RunQuery, null);

            else

                RunQuery(null);

        }

        #endregion

        #region Private Methods

        /// <summary>

        /// Runs the actual Query taking a state object

        /// </summary>

        /// <param name="state">The object state thaat could be 

        /// used to pass some state to the query operation </param>

        private void RunQuery(object state)

        {

            base.BeginQuery();

            try

            {

                List<String> dataLocal = new List<String>();

                String[] lines = null;

                switch (FileName)

                {

                    case "TextFile1":

                        lines = global::TXTDataProvider.

                            Properties.Resources.TextFile1

                            .Split(new String[] { "rn" }, 

                                StringSplitOptions.None);

                        break;

                    case "TextFile2":

                        lines = global::TXTDataProvider.

                            Properties.Resources.TextFile2

                            .Split(new String[] { "rn" }, 

                                StringSplitOptions.None);

                        break;

                    default:

                        break;

                }

                foreach (String line in lines)

                    dataLocal.Add(line);

                ObjectInstance = dataLocal;

            }

            catch

            {

                ObjectInstance = null;

            }

        }

        #endregion

        #region Public Properties

        /// <summary>

        /// Gets or sets a value that indicates 

        /// whether to perform the fetching Asynch or not

        /// </summary>

        public Boolean IsAsync

        {

            get { return isAsync; }

            set 

            {

                isAsync = value;

                OnPropertyChanged(

                    new PropertyChangedEventArgs("IsAsync"));

            }

        }

        /// <summary>

        /// Gets or sets a reference to the data

        /// object.

        /// </summary>

        public object ObjectInstance

        {

            get { return Data; }

            set

            {

                OnQueryFinished(value, null, null, null);

                OnPropertyChanged(

                    new PropertyChangedEventArgs("ObjectInstance"));

            }

        }

        /// <summary>

        /// Gets or sets the name of the FileName to 

        /// read to provide data from.

        /// 

        /// This is obviously a bit contrived, but it does 

        /// assist with the demo code

        /// </summary>

        public String FileName

        {

            get { return fileName; }

            set

            {

                fileName = value;

                OnPropertyChanged(

                    new PropertyChangedEventArgs("FileName"));

            }

        }

        #endregion

    }

}

.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, “Courier New”, courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
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.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }

 

.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, “Courier New”, courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }

And this is the relevant bit of xaml that makes use of this custom DataSourceProvider:

<Window x:Class="TXTDataProvider.Window1"

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

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

    xmlns:local="clr-namespace:TXTDataProvider" WindowStartupLocation="CenterScreen"

    Title="Demo : A simple demo of how to create a custom DataSourceProvider in WPF" 

    Height="600" Width="600" TextElement.FontSize="11">

    <Window.Resources>

        <local:TXTDataSourceProvider x:Key="txtProvider"

              IsAsync="True" FileName="TextFile1"/>

    </Window.Resources>

    <DockPanel LastChildFill="True">

        <ListBox ItemsSource="{Binding Mode=OneTime, 

                    Path=., Source={ StaticResource txtProvider}}" 

                 DockPanel.Dock="Bottom">

            <ListBox.ItemTemplate>

                <DataTemplate>

                    <StackPanel Orientation="Horizontal">

                        <Label Content="Provided Value:" 

                               FontFamily="Arial" 

                               FontWeight="Bold" 

                               Margin="5,0,0,0"/>

                        <Label Content="{Binding}" 

                               FontFamily="Arial" 

                               FontWeight="Normal" 

                               Margin="5,0,0,0"/>

                    </StackPanel>

                </DataTemplate>

            </ListBox.ItemTemplate>

        </ListBox>

    </DockPanel>

</Window>

.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, “Courier New”, courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }

And here is what it looks like when it runs:

As always here is a small demo project. Enjoy

http://dl.dropbox.com/u/2600965/Blogposts/2010/02/TXTDataProvider.zip