This article introduces the “DomainDataSource” available in Silverlight (using WCF RIA Services). It also discusses working with query parameters using “DomainDataSource.”
To make this article simple, I managed to create a simple Silverlight 4.0 application which consumes a WCF RIA Service created using the WCF RIA Service Library. If you are not familiar with developing applications using the WCF RIA Service Library and Silverlight 4.0, check out this beginner’s article.
The entire source code for this article is available in the form of a free downloadable zip file. The solution was developed using Microsoft Visual Studio 2010 Ultimate Edition with Microsoft Silverlight 4.0 on Windows 7 Ultimate edition. I didn’t really test it in any other environment. I request that you post in the discussion area if you have any problems with execution.
Introducing DomainDataSource in Silverlight 4.0
In my previous articles, I explained how to deal with WCF RIA Service from Silverlight 4.0 in various ways. In this article, I would like to introduce the “DomainDataSource” object.
“DomainDataSource” is mainly used to simplify communication between a WCF RIA Service and a Silverlight 4.0 application (without writing too much code-behind). We can leverage “DomainDataSource” to call various operations against the WCF RIA Service using declarative syntax (XAML).
Let us start with an example. The following is the code which lays out a Silverlight DataGrid. We use this DataGrid to show information pulled from the WCF RIA Service using “DomainDataSource.”
“DomainDataSource” is an advanced control which directly works against the WCF RIA service to pull or manipulate data. The main power of this control is that it can be customized declaratively (apart from supporting code-behind).
To retrieve data from the WCF RIA service, we usually start with entity queries. The entity queries execute against a database; the result set is captured in the form of a collection (of entities), and finally put into the “context” object (declared and defined at client).
The entire process explained in the previous paragraph can be automated using a single “DomainDataSource” element. Let us consider the following snippet (taken from the previous section):
Let us try to understand the above code one step at a time:
• DomainDataSource exists in System.Windows.Controls.DomainServices assembly (in this case, the namespace is “riaControls”).
• It is logical control/element (does not have any user interface).
• DomainDataSource works closely and tightly with a DomainContext (in this case, it is “EmpMgrDomainSvc”).
• DomainDataSource pulls data into its context (defined in the previous step) using an entity query supported by the respective DomainContext (in this case, it is “QueryName”).
• Once we specify “AutoLoad=True,” the DomainContext gets automatically instantiated and executes the query specified through “QueryName.”
If we need to handle errors during communication, this can be easily achieved through code-behind as shown below:
Private Sub EmpDomDataSource_LoadedData(ByVal sender As Object, ByVal e As System.Windows.Controls.LoadedDataEventArgs) Handles EmpDomDataSource.LoadedData If e.HasError Then System.Windows.MessageBox.Show(e.Error.ToString, "Load Error", System.Windows.MessageBoxButton.OK) e.MarkErrorAsHandled() End If End Sub
In previous sections, we worked with the DomainDataSource control directly using declarative syntax. In this section, we will dynamically execute a query through DomainDataSource using code-behind.
Partial Public Class DdsQryCodeBehind Inherits UserControl
Public Sub New() InitializeComponent() End Sub
Private Sub btnLoad_Click(ByVal sender As System.Object, ByVal e As System.Windows.RoutedEventArgs) Handles btnLoad.Click Dim oDdsrc As DomainDataSource = Me.Resources("EmpDomDataSource") oDdsrc.QueryName = "GetEmps" oDdsrc.LoadSize = 15 oDdsrc.Load() End Sub
End Class
The above code is pretty self-explanatory. All we do is get the DomainDataSource, provide the QueryName and LoadSize and finally call the “Load” method to execute the query.
Modify App.xaml.vb as shown below (to work with this form):
Private Sub Application_Startup(ByVal o As Object, ByVal e As StartupEventArgs) Handles Me.Startup
Me.RootVisual = New DdsQryCodeBehind()
End Sub
Once you execute the above form, when you click on the button, you should see the output shown below:
In previous sections, we worked with the DomainDataSource element with entity queries which do not have any parameters. In this section, we will try to execute entity queries with parameters using the DomainDataSource.
Let us add a partial class which extends the domain service “EmpMgrDomainSvc” (in “BusinessLib” project) as follows:
Partial Public Class EmpMgrDomainSvc
Public Function GetEmpsByDeptno(ByVal deptno As String) As IQueryable(Of emp) 'better to use IValueConverter in this case Dim iValue As Integer If Integer.TryParse(deptno, iValue) Then Return Me.ObjectContext.emps.Where(Function(c) c.deptno = iValue) Else Return Nothing End If End Function
End Class
The above adds a new method, “GetEmpsByDeptno” (with “deptno” as parameter) to “EmpMgrDomainSvc.” Now, we try to execute the above using the “DomainDataSource.”
In the above code, we assigned the “GetEmpsByDeptno” query to DomainDataSource. As the “GetEmpsByDeptno” method accepts a “Deptno” parameter, we need to provide the parameter value when trying to execute the query. It was done with the following:
Once we execute the above form, the output would look similar to the following:
My upcoming articles will focus on control parameters, sorting, grouping, filtering and paginating using the “DomainDataSource” element. I hope you enjoyed the article; any suggestions, bugs, errors, enhancements etc. are highly appreciated at http://jagchat.spaces.live.com/.
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