SqlDependency in a Windows Application (ADO.NET)

The following scenario shows how to use the SqlDependency class in a Windows Forms application. To demonstrate how notifications work, you will create two applications: a watcher to process query notifications, and an updater to modify the data that the watcher is monitoring.

The watcher application is a Windows Forms application that loads product data into a DataSet from the AdventureWorks SQL Server 2005 sample database. The DataSet is filled using a SqlDataAdapter object that is bound to a DataGridView control. In order to receive notifications, a SqlDependency object is created and bound to the SqlCommand object used by the SqlDataAdapter. The SqlDependency object exposes a single event, OnChange. The handler that is registered to process the notifications performs the necessary actions to switch from the notifying thread pool thread to the UI thread and then re-registers to receive notifications.

1. Create a new Windows Application project named "Data Watcher".

2. In Forms Designer, select the default form. Change the Text property to Inventory Watcher.

3. Add a Label control to the form. Dock the label control to the bottom of the form.

4. Add a ListBox control in the upper left of the form. Size it for approximately three lines of text.

5. Add a DataGridView below the ListBox control.

6. Add a Button control to the form and position it to the right of the ListBox control. Change its Text property to Get Data.

7. Open the form's class module and add the following code to the top of the file, above the class definition.

   Option Strict On
   Option Explicit On
   
   Imports System.ComponentModel
   Imports System.Data.SqlClient
   Imports System.Security.Permissions
   
   using System.Data.SqlClient;
   using System.Security.Permissions;
   

8. In the declaration section of the class, add the following items:

   Private changeCount As Integer = 0
   
   Private Const tableName As String = "Inventory"
   Private Const statusMessage As String = _
     "{0} changes have occurred."
   
   ' The following objects are reused
   ' for the lifetime of the application.
   Private connection As SqlConnection = Nothing
   Private command As SqlCommand = Nothing
   Private dataToWatch As DataSet = Nothing
   

9. In the form, create a new method called CanRequestNotifications. This method will verify the application has permissions to request notifications from the server.

   Private Function CanRequestNotifications() As Boolean
       ' In order to use the callback feature of the
       ' SqlDependency, the application must have
       ' the SqlClientPermission permission.
       Try
           Dim perm As New SqlClientPermission( _
               PermissionState.Unrestricted)
   
           perm.Demand()
           Return True
   
       Catch ex As Exception
           Return False
       End Try
   End Function
   

10. In the form's Load event, use the return value from CanRequestNotifications to set the Enabled property of the form's only button.

    Private Sub Form1_Load(ByVal sender As System.Object, _
        ByVal e As System.EventArgs) Handles MyBase.Load
    
        Button1.Enabled = CanRequestNotifications()
    End Sub
    

11. Add two helper methods, GetConnectionString and GetSQL. The defined connection string uses integrated security. You will need to verify that the account you are using has the necessary database permissions and that the sample database, AdventureWorks, has notifications enabled. For more information, see Enabling Query Notifications (ADO.NET).

    Private Function GetConnectionString() As String
        ' To avoid storing the connection string in your code,
        ' you can retrive it from a configuration file.
        Return "Data Source=(local);Integrated Security=true;" & _
         "Initial Catalog=AdventureWorks;"
    End Function
    
    Private Function GetSQL() As String
        Return "SELECT Production.Product.ProductID, " & _
        "Production.Product.Name, Production.Location.Name AS Location, " & _
        "Production.ProductInventory.Quantity FROM Production.Product " & _
        "INNER JOIN Production.ProductInventory " & _
        "ON Production.Product.ProductID = " & _
        "Production.ProductInventory.ProductID " & _
        "INNER JOIN Production.Location " & _
        "ON Production.ProductInventory.LocationID = " & _
        "Production.Location.LocationID " & _
        "WHERE ( Production.ProductInventory.Quantity <= @Quantity ) " & _
        "ORDER BY Production.ProductInventory.Quantity, Production.Product.Name;"
    End Function
    

12. In order to receive notifications when data on the server changes, the application needs an event handler that matches the signature of the OnChangeEventHandler delegate. The procedure needs to catch the event and switch from the worker thread to the UI thread. Add the following code to the form's module:

    Private Sub dependency_OnChange( _
        ByVal sender As Object, ByVal e As SqlNotificationEventArgs)
    
        ' This event will occur on a thread pool thread.
        ' It is illegal to update the UI from a worker thread
        ' The following code checks to see if it is safe
        ' update the UI.
        Dim i As ISynchronizeInvoke = CType(Me, ISynchronizeInvoke)
    
        ' If InvokeRequired returns True, the code
        ' is executing on a worker thread.
        If i.InvokeRequired Then
            ' Create a delegate to perform the thread switch
            Dim tempDelegate As New OnChangeEventHandler( _
                AddressOf dependency_OnChange)
    
            Dim args() As Object = {sender, e}
    
            ' Marshal the data from the worker thread
            ' to the UI thread.
            i.BeginInvoke(tempDelegate, args)
    
            Return
        End If
    
        ' Remove the handler since it's only good
        ' for a single notification
        Dim dependency As SqlDependency = _
            CType(sender, SqlDependency)
    
        RemoveHandler dependency.OnChange, _
           AddressOf dependency_OnChange
    
        ' At this point, the code is executing on the
        ' UI thread, so it is safe to update the UI.
        changeCount += 1
        Me.Label1.Text = String.Format(statusMessage, changeCount)
    
        ' Add information from the event arguments to the list box
        ' for debugging purposes only.
        With Me.ListBox1.Items
            .Clear()
            .Add("Info:   " & e.Info.ToString())
            .Add("Source: " & e.Source.ToString())
            .Add("Type:   " & e.Type.ToString())
        End With
    
        ' Reload the dataset that's bound to the grid.
        GetData()
    End Sub
    

13. In order to receive notifications, the application must register a SqlDependency object with the SqlCommand object used to obtain the application's data. Add a method called GetData as follows:

    Private Sub GetData()
        ' Empty the dataset so that there is only
        ' one batch worth of data displayed.
        dataToWatch.Clear()
    
        ' Make sure the command object does not already have
        ' a notification object associated with it.
        command.Notification = Nothing
    
        ' Create and bind the SqlDependency object
        ' to the command object.
        Dim dependency As New SqlDependency(command)
        AddHandler dependency.OnChange, AddressOf dependency_OnChange
    
        Using adapter As New SqlDataAdapter(command)
            adapter.Fill(dataToWatch, tableName)
    
            Me.DataGridView1.DataSource = dataToWatch
            Me.DataGridView1.DataMember = tableName
        End Using
    End Sub
    

14. Add an event handler for the Click event in the form's only button, and put the following code in the handler body:

    Private Sub Button1_Click(ByVal sender As System.Object, _
        ByVal e As System.EventArgs) Handles Button1.Click
        changeCount = 0
        Me.Label1.Text = String.Format(statusMessage, changeCount)
    
        ' Remove any existing dependency connection, then create a new one.
        SqlDependency.Stop(GetConnectionString())
        SqlDependency.Start(GetConnectionString())
    
        If connection Is Nothing Then
            connection = New SqlConnection(GetConnectionString())
        End If
        If command Is Nothing Then
            ' GetSQL is a local procedure that returns
            ' a paramaterized SQL string. You might want
            ' to use a stored procedure in your application.
            command = New SqlCommand(GetSQL(), connection)
    
            Dim prm As New SqlParameter("@Quantity", SqlDbType.Int)
            prm.Direction = ParameterDirection.Input
            prm.DbType = DbType.Int32
            prm.Value = 100
            command.Parameters.Add(prm)
        End If
    
        If dataToWatch Is Nothing Then
            dataToWatch = New DataSet()
        End If
    
        GetData()
    End Sub
    

15. In the form's FormClosed event, add the following code to clean up the dependency and database connections:

    Private Sub Form1_FormClosed(ByVal sender As System.Object, _
        ByVal e As System.Windows.Forms.FormClosedEventArgs) _
        Handles MyBase.FormClosed
        SqlDependency.Stop(GetConnectionString())
        If connection IsNot Nothing Then
            connection.Close()
        End If
    End Sub
    

With the watcher application completed, you will need to create the updater application and then run them together.

The updater application provides a simple interface to modify the set of data that is being monitored by the watcher application. The updater in this example is also a Windows Application, but any type of application can be used to update the data. Follow these steps to create the updater application:

1. Create a new Windows Application project called "Data Updater".

2. In Forms Designer, select the default form. In the property grid, change the Text property to "Inventory Updater".

3. Add a Label control and a TextBox control to form. Change the Text property of the label to Product ID and the Name property of the text box to "txtProductID".

4. Add another label and text box. Change the Text property of the label to Quantity and the Name property of the text box to "txtQuantity".

5. Add a Button control and set its Text property to "Update".

6. Add the following directives to the form class:

   Option Strict On
   Option Explicit On
   
   Imports System.Data
   Imports System.Data.SqlClient
   
   using System.Data
   using System.Data.SqlClient;
   

7. In the declaration section of the class, add the following items:

   ' The following objects are reused
   ' for the lifetime of the application.
   Private connection As SqlConnection = Nothing
   Private command As SqlCommand = Nothing
   

8. Add two helper methods, GetConnectionString and GetSQL, to the form. They should look like the following:

   Private Function GetConnectionString() As String
       ' To avoid storing the connection string in your code,
       ' you can retrive it from a configuration file.
       Return "Data Source=(local);Integrated Security=true;" & _
         "Initial Catalog=AdventureWorks;"
   End Function
   
   Private Function GetSQL() As String
       Return "UPDATE Production.ProductInventory " & _
       "SET Production.ProductInventory.Quantity = @Quantity " & _
       "WHERE Production.ProductInventory.ProductID = @ProductID;"
   End Function
   

9. In the Click event of the Get Data button, add the following code:

   Private Sub Button1_Click(ByVal sender As System.Object, _
       ByVal e As System.EventArgs) Handles Button1.Click
   
       Dim productID As Integer = CInt(txtProductID.Text)
       Dim quantity As Integer = CInt(txtQuantity.Text)
   
       If connection Is Nothing Then
           connection = New SqlConnection(GetConnectionString())
           connection.Open()
       End If
   
       If command Is Nothing Then
           ' GetSQL is a local procedure that returns
           ' a paramaterized SQL string. You might want
           ' to use a stored procedure in your applicaiton.
           command = New SqlCommand(GetSQL(), connection)
   
           Dim param As New SqlParameter("@Quantity", SqlDbType.Int)
           param.Direction = ParameterDirection.Input
           param.DbType = DbType.Int32
           command.Parameters.Add(param)
   
           param = New SqlParameter("@ProductID", SqlDbType.Int)
           param.Direction = ParameterDirection.Input
           param.DbType = DbType.Int32
           command.Parameters.Add(param)
       End If
   
       command.Parameters("@Quantity").Value = quantity
       command.Parameters("@ProductID").Value = productID
   
       Dim rowsAffected As Integer = command.ExecuteNonQuery()
   
       MessageBox.Show(rowsAffected & " records updated.", "Update")
   End Sub
   

10. Finally, add the following code to the form's FormClosed event handler:

    Private Sub Form1_FormClosed(ByVal sender As System.Object, _
        ByVal e As System.Windows.Forms.FormClosedEventArgs) _
        Handles MyBase.FormClosed
    
        If connection IsNot Nothing Then
            connection.Close()
        End If
    End Sub
    

Compile and run both applications. Click Get Data on the watcher application to fill the application's grid with data and register a notification request. Examine the data in the grid to find a product ID with an inventory quantity of zero. Switch to the updater application, enter the product ID and a new quantity of one, and click Update. You should see the watcher application automatically update itself moments after the updater changes the data on the server. Observe that the ListBox control displays information about the update.

Query Notifications in SQL Server (ADO.NET)