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Silverlight 4.0 Data Manipulation Using WCF RIA Services
This article focuses on manipulating data (inserting, updating, deleting, saving and refreshing) using WCF RIA Services and Silverlight 4.0 in a raw manner. By this I mean that we will not use the DomainDataSource and DataForm controls of Silverlight 4.0.
To keep this article simple, I created 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 available at http://jagchat.spaces.live.com/blog/cns!41050F68F010A662!4439.entry.
This is an extension to my previous article titled “Retrieving Data from WCF RIA Services using Silverlight 4.0.” You can view my previous articles at http://www.aspfree.com/cp/bio/Jagadish-Chatarji
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.
Modifying Entities at Silverlight application
In my previous article, I explained how to retrieve data from WCF RIA Services in various ways. In this section, we are going to edit/modify entities available in a Silverlight application.
The following would send a request to a WCF RIA Service for all “emp” entities and make them available locally (at the Silverlight application):
Private oCtxt As New BusinessLib.Web.EmpMgrDomainSvc
Public Sub New()
InitializeComponent()
Me.dgEmp.ItemsSource = oCtxt.emps
oCtxt.Load(oCtxt.GetEmpsQuery())
End Sub
From the above, we understand that “oCtxt” holds all entities, and we can use the same object to add/modify/remove various entities.
To modify a particular entity, we need to make textboxes bind to the properties of the same entity. As all of our entities are currently listed in datagrid, I would like to make textboxes bind to the selected row of the datagrid. This can be achieved as shown below:
Private Sub dgEmp_SelectionChanged(ByVal sender As System.Object, ByVal e As System.Windows.Controls.SelectionChangedEventArgs) Handles dgEmp.SelectionChanged
If dgEmp.SelectedItem IsNot Nothing Then
Me.lytEmpForm.DataContext = dgEmp.SelectedItem
End If
End Sub
All textboxes (except txtEmpno) are two-way bound to the properties of the “Emp” entity type, and all of those are contained in “lytEmpForm.” Once we set the “DataContext” property of “lytEmpForm” to an entity object, all textboxes will pull information (using properties) from the same object and get bound automatically. This is illustrated in the following figure:
Apart from the selected row, I also added functionality to search for an employee. This is illustrated below:
Private Sub btnSearch_Click(ByVal sender As System.Object, ByVal e As System.Windows.RoutedEventArgs) Handles btnSearch.Click
Dim oEmp = oCtxt.emps.SingleOrDefault(Function(p) p.empno = Me.txtEmpno.Text)
If oEmp Is Nothing Then
MessageBox.Show("Employee not found")
Else
Me.lytEmpForm.DataContext = oEmp
End If
End Sub
In the above case, I search for an entity in the list of entities owned by “oCtxt” and directly assign the same as “DataContext” to “lytEmpForm.” You can understand this from the following figure:
Once the textboxes reflect the data from the selected entity, you can directly edit the data available in the textboxes. Modifying the data in the textboxes will automatically reflect back to the entities, and finally to the datagrid, too!
NOTE: All of the modifications are preserved at the client (in this case, it is the Silverlight application) unless they are explicitly saved (which is covered in upcoming sections).
In the previous section, we saw how to modify existing entities. In this section, we will work on adding or deleting entities from the “oCtxt” object.
Adding or removing entities is a straightforward process. All we have to do is manipulate the entity set (which similar to collection) available in the context.
The following is the code that lets you add a new entity:
Private Sub btnAddNew_Click(ByVal sender As System.Object, ByVal e As System.Windows.RoutedEventArgs) Handles btnAddNew.Click
Dim oEmp As New BusinessLib.Web.emp
oCtxt.emps.Add(oEmp)
Me.txtEmpno.SetBinding(TextBox.TextProperty,
New System.Windows.Data.Binding With
{
.Path = New PropertyPath("empno"),
.Mode = Data.BindingMode.TwoWay
})
Me.lytEmpForm.DataContext = oEmp
End Sub
In the above code, we cause “txtEmpno” to be dynamically bound to the “empno” property of the newly-created “emp” entity object. Adding a new entity would give the result shown below:
The following is the code required to delete an existing entity:
Private Sub btnDelete_Click(ByVal sender As System.Object, ByVal e As System.Windows.RoutedEventArgs) Handles btnDelete.Click
If Me.lytEmpForm.DataContext Is Nothing Then
MessageBox.Show("Employee not selected to delete")
Exit Sub
End If
oCtxt.emps.Remove(Me.lytEmpForm.DataContext)
End Sub
NOTE: All of the modifications are preserved at the client (in this case, it is the Silverlight application) unless they are explicitly saved (which is covered in the next section).
Imagine that I am adding a new employee with an already-existing empno (Primary key validation). The error is displayed as follows:
The above code would save the current changes to the content to the database, but not the other way around. That is, the content will not reflect the changes made at the database level (while the user is locally manipulating the Silverlight application).
The following is the code required to save and refresh the contents of “Context” objects based on database changes (which are unknown to the Silverlight application):
Private Sub btnSaveAndRefresh_Click(ByVal sender As System.Object, ByVal e As System.Windows.RoutedEventArgs) Handles btnSaveAndRefresh.Click
In the above code, I am calling the “GetChanges()” method available in the “EntityContainer” of the “oCtxt” object to list all of the modifications I made to the entire context.
After modifying one entity and removing another, the output from the above code would look like the following:
We can also reject all changes made to EntitySet as shown below:
Private Sub btnReject_Click(ByVal sender As System.Object, ByVal e As System.Windows.RoutedEventArgs) Handles btnReject.Click
If oCtxt.HasChanges Then
oCtxt.RejectChanges()
MessageBox.Show("Cancelled/Rejected all changes")
Else
MessageBox.Show("No changes to reject")
End If
End Sub
Make sure that “RejectChanges” of “oCtxt” object will cancel all modifications (throughout all entity sets) available locally and will not touch any at the server level.
After a successful cancellation of all changes, the output would look like this:
I hope you enjoyed the article and any suggestions, bugs, errors, enhancements etc. are highly appreciated at http://jagchat.spaces.live.com
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