SqlCommand.Cancel Methode

Definitie

Naamruimte:
System.Data.SqlClient
Assembly:
System.Data.dll

Probeert de uitvoering van een SqlCommand.

public:
 virtual void Cancel();
public:
 override void Cancel();
public void Cancel();
public override void Cancel();
abstract member Cancel : unit -> unit
override this.Cancel : unit -> unit
override this.Cancel : unit -> unit
Public Sub Cancel ()
Public Overrides Sub Cancel ()

Implementeringen

Cancel()

Voorbeelden

In het volgende voorbeeld ziet u het gebruik van de methode Cancel.

using System;
using System.Data;
using System.Data.SqlClient;
using System.Threading;

class Program
{
    private static SqlCommand m_rCommand;

    public static SqlCommand Command
    {
        get { return m_rCommand; }
        set { m_rCommand = value; }
    }

    public static void Thread_Cancel()
    {
        Command.Cancel();
    }

    static void Main()
    {
        string connectionString = GetConnectionString();
        try
        {
            using (SqlConnection connection = new SqlConnection(connectionString))
            {
                connection.Open();

                Command = connection.CreateCommand();
                Command.CommandText = "DROP TABLE TestCancel";
                try
                {
                    Command.ExecuteNonQuery();
                }
                catch { }

                Command.CommandText = "CREATE TABLE TestCancel(co1 int, co2 char(10))";
                Command.ExecuteNonQuery();
                Command.CommandText = "INSERT INTO TestCancel VALUES (1, '1')";
                Command.ExecuteNonQuery();

                Command.CommandText = "SELECT * FROM TestCancel";
                SqlDataReader reader = Command.ExecuteReader();

                Thread rThread2 = new Thread(new ThreadStart(Thread_Cancel));
                rThread2.Start();
                rThread2.Join();

                reader.Read();
                System.Console.WriteLine(reader.FieldCount);
                reader.Close();
            }
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex.Message);
        }
    }
    static private string GetConnectionString()
    {
        // To avoid storing the connection string in your code,
        // you can retrieve it from a configuration file.
        return "Data Source=(local);Initial Catalog=AdventureWorks;"
            + "Integrated Security=SSPI";
    }
}

Imports System.Data
Imports System.Data.SqlClient
Imports System.Threading

Module Module1
    Private m_rCommand As SqlCommand

    Public Property Command() As SqlCommand
        Get
            Return m_rCommand
        End Get
        Set(ByVal value As SqlCommand)
            m_rCommand = value
        End Set
    End Property

    Public Sub Thread_Cancel()
        Command.Cancel()
    End Sub

    Sub Main()
        Dim connectionString As String = GetConnectionString()

        Try
            Using connection As New SqlConnection(connectionString)

                connection.Open()

                Command = connection.CreateCommand()
                Command.CommandText = "DROP TABLE TestCancel"
                Try
                    Command.ExecuteNonQuery()
                Catch
                End Try

                Command.CommandText = "CREATE TABLE TestCancel(co1 int, co2 char(10))"
                Command.ExecuteNonQuery()
                Command.CommandText = "INSERT INTO TestCancel VALUES (1, '1')"
                Command.ExecuteNonQuery()

                Command.CommandText = "SELECT * FROM TestCancel"
                Dim reader As SqlDataReader = Command.ExecuteReader()

                Dim rThread2 As New Thread( _
                    New ThreadStart(AddressOf Thread_Cancel))

                rThread2.Start()
                rThread2.Join()

                reader.Read()
                Console.WriteLine(reader.FieldCount)
                reader.Close()
            End Using

        Catch ex As Exception
            Console.WriteLine(ex.Message)
        End Try
    End Sub

    Private Function GetConnectionString() As String
        ' To avoid storing the connection string in your code,  
        ' you can retrieve it from a configuration file.
        Return "Data Source=(local);Initial Catalog=AdventureWorks;" _
           & "Integrated Security=SSPI;"
    End Function
End Module

Opmerkingen

Als er niets te annuleren is, gebeurt er niets. Als er echter een opdracht wordt uitgevoerd en de poging om te annuleren mislukt, wordt er geen uitzondering gegenereerd.

In sommige zeldzame gevallen, als u ExecuteReader aanroept, roept u Close (impliciet of expliciet) aan voordat u Cancel aanroept en vervolgens Cancel aanroept, wordt de opdracht annuleren niet verzonden naar SQL Server en kan de resultatenset blijven streamen nadat u Close hebt aangeroepen. Om dit te voorkomen, moet u bellen Cancel voordat u de lezer of verbinding sluit.

Van toepassing op

Zie ook