ObjectDataSource.Deleting Evento
Definizione
Importante
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Si verifica prima di un'operazione Delete().
public:
event System::Web::UI::WebControls::ObjectDataSourceMethodEventHandler ^ Deleting;public event System.Web.UI.WebControls.ObjectDataSourceMethodEventHandler Deleting;member this.Deleting : System.Web.UI.WebControls.ObjectDataSourceMethodEventHandler Public Custom Event Deleting As ObjectDataSourceMethodEventHandler Tipo evento
Esempio
In questa sezione sono riportati due esempi di codice. Nel primo esempio di codice viene illustrato come utilizzare un ObjectDataSource oggetto con un oggetto business e un GridView controllo per eliminare i dati. Il secondo esempio di codice mostra la EmployeeLogic classe usata nel primo esempio di codice.
Nell'esempio di codice seguente viene illustrato come utilizzare un ObjectDataSource controllo con un oggetto business e un GridView controllo per eliminare i dati. Inizialmente, il GridView controllo visualizza un set di tutti i dipendenti, utilizzando il metodo specificato dalla SelectMethod proprietà per recuperare i dati dall'oggetto EmployeeLogic . Poiché la AutoGenerateDeleteButton proprietà è impostata su true, il GridView controllo visualizza automaticamente un pulsante Elimina .
Se si fa clic sul pulsante Elimina , l'operazione di eliminazione viene eseguita utilizzando il metodo specificato dalla DeleteMethod proprietà e tutti i parametri specificati nell'insieme DeleteParameters . In questo esempio di codice vengono eseguiti anche alcuni passaggi di pre-elaborazione e post-elaborazione. Il NorthwindEmployeeDeleting delegato viene chiamato per gestire l'evento Deleting prima dell'esecuzione dell'operazione e il NorthwindEmployeeDeleted delegato viene chiamato per gestire l'evento Deleted dopo il completamento dell'operazione per eseguire la gestione delle eccezioni. In questo esempio di codice, se viene generata un'eccezione NorthwindDataException , viene gestita dal NorthwindEmployeeDeleted metodo .
<%@ Register TagPrefix="aspSample" Namespace="Samples.AspNet.CS" Assembly="Samples.AspNet.CS" %>
<%@ Import namespace="Samples.AspNet.CS" %>
<%@ Page language="c#" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<script runat="server">
private void NorthwindEmployeeDeleting(object source, ObjectDataSourceMethodEventArgs e)
{
// The GridView passes the ID of the employee
// to be deleted. However, the buisiness object, EmployeeLogic,
// requires a NorthwindEmployee parameter, named "ne". Create
// it now and add it to the parameters collection.
IDictionary paramsFromPage = e.InputParameters;
if (paramsFromPage["EmpID"] != null) {
NorthwindEmployee ne
= new NorthwindEmployee( Int32.Parse(paramsFromPage["EmpID"].ToString()));
// Remove the old EmpID parameter.
paramsFromPage.Clear();
paramsFromPage.Add("ne", ne);
}
}
private void NorthwindEmployeeDeleted(object source, ObjectDataSourceStatusEventArgs e)
{
// Handle the Exception if it is a NorthwindDataException
if (e.Exception != null)
{
// Handle the specific exception type. The ObjectDataSource wraps
// any Exceptions in a TargetInvokationException wrapper, so
// check the InnerException property for expected Exception types.
if (e.Exception.InnerException is NorthwindDataException)
{
Label1.Text = e.Exception.InnerException.Message;
// Because the exception is handled, there is
// no reason to throw it.
e.ExceptionHandled = true;
}
}
}
</script>
<html xmlns="http://www.w3.org/1999/xhtml" >
<head>
<title>ObjectDataSource - C# Example</title>
</head>
<body>
<form id="Form1" method="post" runat="server">
<asp:gridview
id="GridView1"
runat="server"
datasourceid="ObjectDataSource1"
autogeneratedeletebutton="true"
autogeneratecolumns="false"
datakeynames="EmpID">
<columns>
<asp:boundfield headertext="EmpID" datafield="EmpID" />
<asp:boundfield headertext="First Name" datafield="FirstName" />
<asp:boundfield headertext="Last Name" datafield="LastName" />
</columns>
</asp:gridview>
<asp:objectdatasource
id="ObjectDataSource1"
runat="server"
selectmethod="GetAllEmployees"
deletemethod="DeleteEmployee"
ondeleting="NorthwindEmployeeDeleting"
ondeleted="NorthwindEmployeeDeleted"
typename="Samples.AspNet.CS.EmployeeLogic">
<deleteparameters>
<asp:parameter name="EmpID" type="Int32" />
</deleteparameters>
</asp:objectdatasource>
<asp:label id="Label1" runat="server" />
</form>
</body>
</html>
<%@ 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"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<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.Clear()
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
</script>
<html xmlns="http://www.w3.org/1999/xhtml" >
<head>
<title>ObjectDataSource - VB Example</title>
</head>
<body>
<form id="Form1" method="post" runat="server">
<asp:gridview
id="GridView1"
runat="server"
datasourceid="ObjectDataSource1"
autogeneratedeletebutton="true"
autogeneratecolumns="false"
datakeynames="EmpID">
<columns>
<asp:boundfield headertext="EmpID" datafield="EmpID" />
<asp:boundfield headertext="First Name" datafield="FirstName" />
<asp:boundfield headertext="Last Name" datafield="LastName" />
</columns>
</asp:gridview>
<asp:objectdatasource
id="ObjectDataSource1"
runat="server"
selectmethod="GetAllEmployees"
deletemethod="DeleteEmployee"
ondeleting="NorthwindEmployeeDeleting"
ondeleted="NorthwindEmployeeDeleted"
typename="Samples.AspNet.VB.EmployeeLogic">
<deleteparameters>
<asp:parameter name="EmpID" type="Int32" />
</deleteparameters>
</asp:objectdatasource>
<asp:label id="Label1" runat="server" />
</form>
</body>
</html>
Nell'esempio di codice seguente viene illustrata la EmployeeLogic classe usata nell'esempio di codice precedente.
namespace Samples.AspNet.CS {
using System;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Data.SqlClient;
using System.Web.UI;
using System.Web.UI.WebControls;
//
// EmployeeLogic is a stateless business object that encapsulates
// the operations you can perform on a NorthwindEmployee object.
//
public class EmployeeLogic {
// Returns a collection of NorthwindEmployee objects.
public static ICollection GetAllEmployees () {
ArrayList al = new ArrayList();
// Use the SqlDataSource class to wrap the
// ADO.NET code required to query the database.
ConnectionStringSettings cts = ConfigurationManager.ConnectionStrings["NorthwindConnection"];
SqlDataSource sds
= new SqlDataSource(cts.ConnectionString,
"SELECT EmployeeID FROM Employees");
try {
IEnumerable IDs = sds.Select(DataSourceSelectArguments.Empty);
// Iterate through the Enumeration and create a
// NorthwindEmployee object for each ID.
IEnumerator enumerator = IDs.GetEnumerator();
while (enumerator.MoveNext()) {
// The IEnumerable contains DataRowView objects.
DataRowView row = enumerator.Current as DataRowView;
string id = row["EmployeeID"].ToString();
NorthwindEmployee nwe = new NorthwindEmployee(id);
// Add the NorthwindEmployee object to the collection.
al.Add(nwe);
}
}
finally {
// If anything strange happens, clean up.
sds.Dispose();
}
return al;
}
public static NorthwindEmployee GetEmployee(object anID) {
return new NorthwindEmployee(anID);
}
public static void DeleteEmployee(NorthwindEmployee ne) {
bool retval = ne.Delete();
if (! retval) { throw new NorthwindDataException("Employee delete failed."); }
// Delete the object in memory.
ne = null;
}
public static void DeleteEmployeeByID(int anID) {
NorthwindEmployee tempEmp = new NorthwindEmployee(anID);
DeleteEmployee(tempEmp);
}
}
public class NorthwindEmployee {
public NorthwindEmployee () {
ID = DBNull.Value;
lastName = "";
firstName = "";
}
public NorthwindEmployee (object anID) {
this.ID = anID;
ConnectionStringSettings cts = ConfigurationManager.ConnectionStrings["NorthwindConnection"];
SqlConnection conn = new SqlConnection (cts.ConnectionString);
SqlCommand sc =
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());
SqlDataReader sdr = null;
try {
conn.Open();
sdr = sc.ExecuteReader();
// This is not a while loop. It only loops once.
if (sdr != null && sdr.Read()) {
// The IEnumerable contains DataRowView objects.
this.firstName = sdr["FirstName"].ToString();
this.lastName = sdr["LastName"].ToString();
}
else {
throw new NorthwindDataException("Data not loaded for employee id.");
}
}
finally {
try {
if (sdr != null) sdr.Close();
conn.Close();
}
catch (SqlException) {
// Log an event in the Application Event Log.
throw;
}
}
}
private object ID;
public object EmpID {
get { return ID; }
}
private string lastName;
public string LastName {
get { return lastName; }
set { lastName = value; }
}
private string firstName;
public string FirstName {
get { return firstName; }
set { firstName = value; }
}
public bool Delete () {
if (ID.Equals(DBNull.Value)) {
// The Employee object is not persisted.
return true;
}
else {
// 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.
ConnectionStringSettings cts = ConfigurationManager.ConnectionStrings["NorthwindConnection"];
SqlDataSource sds = new SqlDataSource();
try {
sds.ConnectionString = cts.ConnectionString;
sds.DeleteParameters.Add(new Parameter("empID", TypeCode.Int32, this.ID.ToString()));
sds.DeleteCommand = "DELETE FROM [Order Details] " +
"WHERE OrderID IN (SELECT OrderID FROM Orders WHERE EmployeeID=@empID)";
sds.Delete();
sds.DeleteCommand = "DELETE FROM Orders WHERE EmployeeID=@empID";
sds.Delete();
sds.DeleteCommand = "DELETE FROM EmployeeTerritories WHERE EmployeeID=@empID";
sds.Delete();
sds.DeleteCommand = "DELETE FROM Employees WHERE EmployeeID=@empID";
sds.Delete();
return true;
}
finally {
// Clean up resources.
sds.Dispose();
}
}
}
}
public class NorthwindDataException: Exception {
public NorthwindDataException(string msg) : base (msg) { }
}
}
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")
Try
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.
al.Add(nwe)
End While
Finally
' If anything strange happens, clean up.
sds.Dispose()
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
Public Shared Sub DeleteEmployeeByID(anID As Integer)
Dim tempEmp As New NorthwindEmployee(anID)
DeleteEmployee(tempEmp)
End Sub
End Class
Public Class NorthwindEmployee
Public Sub New()
ID = DBNull.Value
aLastName = ""
aFirstName = ""
End Sub
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
Try
conn.Open()
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()
Else
Throw New NorthwindDataException("Data not loaded for employee id.")
End If
Finally
Try
If Not (sdr Is Nothing) Then
sdr.Close()
End If
conn.Close()
Catch se As SqlException
' Log an event in the Application Event Log.
Throw
End Try
End Try
End Sub
Private ID As Object
Public ReadOnly Property EmpID() As Object
Get
Return ID
End Get
End Property
Private aLastName As String
Public Property LastName() As String
Get
Return aLastName
End Get
Set
aLastName = value
End Set
End Property
Private aFirstName As String
Public Property FirstName() As String
Get
Return aFirstName
End Get
Set
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
Else
' 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()
Try
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.Delete()
sds.DeleteCommand = "DELETE FROM Orders WHERE EmployeeID=@empID"
sds.Delete()
sds.DeleteCommand = "DELETE FROM EmployeeTerritories WHERE EmployeeID=@empID"
sds.Delete()
sds.DeleteCommand = "DELETE FROM Employees WHERE EmployeeID=@empID"
sds.Delete()
Return True
Finally
' Clean up resources.
sds.Dispose()
End Try
End If
End Function 'Delete
End Class
Public Class NorthwindDataException
Inherits Exception
Public Sub New(msg As String)
MyBase.New(msg)
End Sub
End Class
End Namespace
Commenti
Gestire l'evento per eseguire un'inizializzazione Deleting aggiuntiva specifica per l'applicazione, per convalidare i valori dei parametri o per modificare i valori dei parametri prima che il ObjectDataSource controllo esegua l'operazione di eliminazione. I parametri sono disponibili come raccolta IDictionary a cui si accede dalla InputParameters proprietà , esposta dall'oggetto ObjectDataSourceMethodEventArgs .
È possibile annullare l'operazione di eliminazione impostando la Cancel proprietà di ObjectDataSourceMethodEventArgs su true.
Per altre informazioni su come gestire gli eventi, vedere la gestione e generazione di eventi.
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