ObjectDataSource.Deleting Event


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Occurs before a Delete operation.

Namespace:   System.Web.UI.WebControls
Assembly:  System.Web (in System.Web.dll)

Public Event Deleting As ObjectDataSourceMethodEventHandler

Handle the Deleting event to perform additional initialization that is specific to your application, to validate the values of parameters, or to change the parameter values before the ObjectDataSource control performs the delete operation. The parameters are available as an IDictionary collection that is accessed by the InputParameters property, which is exposed by the ObjectDataSourceMethodEventArgs object.

You can cancel the delete operation by setting the Cancel property of the ObjectDataSourceMethodEventArgs to true.

For more information about handling events, see NIB: Consuming Events.

This section contains two code examples. The first code example demonstrates how to use an ObjectDataSource object with a business object and a GridView control to delete data. The second code example shows the EmployeeLogic class that is used in the first code example.

The following code example demonstrates how to use an ObjectDataSource control with a business object and a GridView control to delete data. Initially, the GridView control displays a set of all employees, using the method that is specified by the SelectMethod property to retrieve the data from the EmployeeLogic object. Because the AutoGenerateDeleteButton property is set to true, the GridView control automatically displays a Delete button.

If you click the Delete button, the delete operation is performed using the method that is specified by the DeleteMethod property and any parameters that are specified in the DeleteParameters collection. In this code example, some preprocessing and post-processing steps are also performed. The NorthwindEmployeeDeleting delegate is called to handle the Deleting event before the operation is performed, and the NorthwindEmployeeDeleted delegate is called to handle the Deleted event after the operation has completed to perform exception handling. In this code example, if a NorthwindDataException is thrown, it is handled by the NorthwindEmployeeDeleted method.

<%@ Register TagPrefix="aspSample" Namespace="Samples.AspNet.VB" Assembly="Samples.AspNet.VB" %>
<%@ Import namespace="Samples.AspNet.VB" %>
<%@ Page language="vb" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
<script runat="server">
' Called before a Delete operation.
    Private Sub NorthwindEmployeeDeleting(ByVal source As Object, ByVal e As ObjectDataSourceMethodEventArgs)

        ' The GridView passes the ID of the employee
        ' to be deleted. However, the business object, EmployeeLogic,
        ' requires a NorthwindEmployee parameter, named "ne". Create
        ' it now and add it to the parameters collection.
        Dim paramsFromPage As IDictionary = e.InputParameters

        If Not paramsFromPage("EmpID") Is Nothing Then

            Dim ne As New NorthwindEmployee(paramsFromPage("EmpID").ToString())
            ' Remove the old EmpID parameter.
            paramsFromPage.Add("ne", ne)

        End If
    End Sub ' NorthwindEmployeeDeleting

    ' Called after a Delete operation.
    Private Sub NorthwindEmployeeDeleted(ByVal source As Object, ByVal e As ObjectDataSourceStatusEventArgs)
        ' Handle the Exception if it is a NorthwindDataException.
        If Not e.Exception Is Nothing Then

            ' Handle the specific exception type. The ObjectDataSource wraps
            ' any Exceptions in a TargetInvokationException wrapper, so
            ' check the InnerException property for the expected Exception types.
            If e.Exception.InnerException.GetType().Equals(GetType(NorthwindDataException)) Then

                Label1.Text = e.Exception.InnerException.Message
                ' Because the exception is handled, there is
                ' no reason to throw it.
                e.ExceptionHandled = True

            End If
        End If
    End Sub ' NorthwindEmployeeDeleted
<html xmlns="http://www.w3.org/1999/xhtml" >
    <title>ObjectDataSource - VB Example</title>
    <form id="Form1" method="post" runat="server">

            <asp:boundfield headertext="EmpID" datafield="EmpID" />
            <asp:boundfield headertext="First Name" datafield="FirstName" />
            <asp:boundfield headertext="Last Name" datafield="LastName" />

            <asp:parameter name="EmpID" type="Int32" />

        <asp:label id="Label1" runat="server" />


The following code example shows the EmployeeLogic class that is used in the preceding code example.

Imports System
Imports System.Collections
Imports System.Configuration
Imports System.Data
Imports System.Data.SqlClient
Imports System.Web.UI
Imports System.Web.UI.WebControls

Namespace Samples.AspNet.VB
' EmployeeLogic is a stateless business object that encapsulates
' the operations you can perform on a NorthwindEmployee object.
Public Class EmployeeLogic

   ' Return a collection of NorthwindEmployee objects.
   Public Shared Function GetAllEmployees() As ICollection
      Dim al As New ArrayList()

      ' Use the SqlDataSource class to wrap the
      ' ADO.NET code required to query the database.
      Dim cts As ConnectionStringSettings = ConfigurationManager.ConnectionStrings("NorthwindConnection")
      Dim sds As New SqlDataSource(cts.ConnectionString, _
                                  "SELECT EmployeeID FROM Employees")
         Dim IDs As IEnumerable = sds.Select(DataSourceSelectArguments.Empty)

         ' Iterate through the Enumeration and create a
         ' NorthwindEmployee object for each ID.
         Dim enumerator As IEnumerator = IDs.GetEnumerator()
         While enumerator.MoveNext()
            ' The IEnumerable contains DataRowView objects.
            Dim row As DataRowView = CType(enumerator.Current,DataRowView)
            Dim id As String = row("EmployeeID").ToString()
            Dim nwe As New NorthwindEmployee(id)
            ' Add the NorthwindEmployee object to the collection.
         End While
         ' If anything strange happens, clean up.
      End Try

      Return al
   End Function 'GetAllEmployees

   Public Shared Function GetEmployee(anID As Object) As NorthwindEmployee
      Return New NorthwindEmployee(anID)
   End Function 'GetEmployee

   Public Shared Sub DeleteEmployee(ne As NorthwindEmployee)
      Dim retval As Boolean = ne.Delete()
      If Not retval Then
         Throw New NorthwindDataException("Employee delete failed.")
      End If ' Delete the object in memory.
      ne = Nothing
   End Sub 'DeleteEmployee

   Public Shared Sub DeleteEmployeeByID(anID As Integer)
      Dim tempEmp As New NorthwindEmployee(anID)
   End Sub 'DeleteEmployeeByID

End Class 'EmployeeLogic

Public Class NorthwindEmployee

   Public Sub New()
      ID = DBNull.Value
      aLastName = ""
      aFirstName = ""
   End Sub 'NewNew

   Public Sub New(anID As Object)
      Me.ID = anID
      Dim cts As ConnectionStringSettings = ConfigurationManager.ConnectionStrings("NorthwindConnection")
      Dim conn As New SqlConnection(cts.ConnectionString)
      Dim sc As New SqlCommand(" SELECT FirstName,LastName " & _
                               " FROM Employees " & _
                               " WHERE EmployeeID = @empId", conn)
      ' Add the employee ID parameter and set its value.
      sc.Parameters.Add(New SqlParameter("@empId", SqlDbType.Int)).Value = Int32.Parse(anID.ToString())
      Dim sdr As SqlDataReader = Nothing

         sdr = sc.ExecuteReader()

         ' This is not a while loop. It only loops once.
         If Not (sdr Is Nothing) AndAlso sdr.Read() Then
            ' The IEnumerable contains DataRowView objects.
            Me.aFirstName = sdr("FirstName").ToString()
            Me.aLastName = sdr("LastName").ToString()
            Throw New NorthwindDataException("Data not loaded for employee id.")
         End If
            If Not (sdr Is Nothing) Then
            End If
         Catch se As SqlException
            ' Log an event in the Application Event Log.
         End Try
      End Try
   End Sub 'NewNew

   Private ID As Object
   Public ReadOnly Property EmpID() As Object
         Return ID
      End Get
   End Property

   Private aLastName As String
   Public Property LastName() As String
         Return aLastName
      End Get
         aLastName = value
      End Set
   End Property

   Private aFirstName As String
   Public Property FirstName() As String
         Return aFirstName
      End Get
         aFirstName = value
      End Set
   End Property

   Public Function Delete() As Boolean
      If ID.Equals(DBNull.Value) Then
         ' The Employee object is not persisted.
         Return True
         ' The Employee object is persisted.
         ' Use the SqlDataSource control as a convenient wrapper for
         ' the ADO.NET code needed to delete a record from the database.
         Dim cts As ConnectionStringSettings = ConfigurationManager.ConnectionStrings("NorthwindConnection")
         Dim sds As New SqlDataSource()
            sds.ConnectionString = cts.ConnectionString
            sds.DeleteParameters.Add(New Parameter("empID", TypeCode.Int32, Me.ID.ToString()))
            sds.DeleteCommand = "DELETE FROM [Order Details] " & _
                "WHERE OrderID IN (SELECT OrderID FROM Orders WHERE EmployeeID=@empID)"
            sds.DeleteCommand = "DELETE FROM Orders WHERE EmployeeID=@empID"
            sds.DeleteCommand = "DELETE FROM EmployeeTerritories WHERE EmployeeID=@empID"
            sds.DeleteCommand = "DELETE FROM Employees WHERE EmployeeID=@empID"
            Return True
            ' Clean up resources.
         End Try
      End If
   End Function 'Delete
End Class 'NorthwindEmployee

Public Class NorthwindDataException
   Inherits Exception

   Public Sub New(msg As String)
   End Sub 'NewNew

End Class 'NorthwindDataException
End Namespace

.NET Framework
Available since 2.0
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