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Silverlight 4.0: Filtering Data Using DomainDataSource
This article gives a complete idea of the filtering features available with the “DomainDataSource” control in Silverlight (using WCF RIA Services). It discusses how to use both markup and code-behind methodologies to implement filtering against data retrieved from WCF RIA Services.
To make this article simple, I built 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 a 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.
Filtering data using DomainDataSource – the markup way
In my previous articles, I explained the importance of DomainDataSource and how we can query, sort and group data using the same in a Silverlight 4.0 application. In this section, we will focus on filtering the data available in DomainDataSource.
Let's take a close look at the above code. I defined a DomainDataSource named “EmpDomDataSource” which works with a Domain Service context defined as “EmpMgrDomainSvc.” The DomainDataSource works with an entity query named “GetEmps” and loads all entities automatically (“AutoLoad” setting is set to “true”). The DomainDataSource is equipped with a FilterDescriptor, as shown below:
A FilterDescriptor accepts “PropertyPath” and a value for the property. This way, the DomainDatasource filters data based on the property and value defined in the FilterDescriptor. Similarly, we can have any number of FilterDescriptor elements specified as part of the “FilterDescriptors” element.
Finally, DomainDataSource applies the filter, and DataGrid gets bound to DomainDataSource as shown below:
The code-behind way to filter data using DomainDataSource: form design
In the previous section, we saw how to filter data in DomainDataSource using a simple change in markup. In this section, we will try to accomplish the same using code-behind.
The above creates a stack panel which acts as a container to all controls placed next to each other in a horizontal manner. From the above, you should understand that the stack panel contains a label, a textbox and two buttons sitting next to each other.
Finally, we have the DataGrid, which sits in second row of the whole form. This occupies the rest of the space after the first row (with the stack panel) is rendered. It is currently bound to “EmpDomDataSource,” which is defined as follows:
Partial Public Class DdsFilterCodeBehind Inherits UserControl
Public Sub New() InitializeComponent() End Sub
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
Private Sub btnApplyFilter_Click(ByVal sender As System.Object, ByVal e As System.Windows.RoutedEventArgs) Handles btnApplyFilter.Click Me.EmpDomDataSource.FilterDescriptors.Clear() Dim oFilter As New FilterDescriptor With { .PropertyPath = "deptno", .Value = Me.txtDeptFilter.Text } Me.EmpDomDataSource.FilterDescriptors.Add(oFilter) End Sub
Private Sub btnClearFilter_Click(ByVal sender As System.Object, ByVal e As System.Windows.RoutedEventArgs) Handles btnClearFilter.Click Me.EmpDomDataSource.FilterDescriptors.Clear() End Sub End Class
The DomainDataSource element contains the “FilterDescriptors” collection. We can add as many filter parameters as possible to this collection. The moment we add any object to “FilterDescriptors,” DomainDataSource automatically filters data immediately, and this will be reflected automatically in the data grid.
The output for the above would look similar to the following:
Working with filter operators using DomainDataSource
In all previous sections we saw how to apply filters to a DomainDataSource using “FilterDescriptors.” All of those filters work with the “equal” condition by default.
In detail, the property path (available as part of the FilterDescriptor) gets checked with the value we provide, and the object will be selected if and only if both match. But, I may have a scenario that is different from direct matching. For example, say I want to see all the employees that have a salary above 6000. This can be accomplished by providing filter operators as shown below:
From the above code, you can observe that the FilterDescriptor has a new attribute, “Operator.” It is an enumeration with a pre-defined set of constants which work as operators. The output for the above would look similar to the following:
My upcoming articles will focus more on 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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