SqlCommand.Cancel Método

Definição

Tenta cancelar a execução de um SqlCommand.Tries to cancel the execution of a SqlCommand.

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

Implementações

Exemplos

O exemplo a seguir demonstra o uso do método Cancel.The following example demonstrates the use of the Cancel method.

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

Comentários

Se não houver nada para cancelar, nada acontecerá.If there is nothing to cancel, nothing occurs. No entanto, se houver um comando em processo e a tentativa de cancelamento falhar, nenhuma exceção será gerada.However, if there is a command in process, and the attempt to cancel fails, no exception is generated.

Em alguns casos raros, se você chamar ExecuteReader , então chamar Close (implícita ou explicitamente) antes de chamar e, Cancel em seguida Cancel , chamar, o comando Cancel não será enviado para SQL Server e o conjunto de resultados poderá continuar a transmitir após a chamada Close .In some rare cases, if you call ExecuteReader, then call Close (implicitly or explicitly) before calling Cancel, and then call Cancel, the cancel command will not be sent to SQL Server and the result set can continue to stream after you call Close. Para evitar isso, certifique-se de chamar Cancel antes de fechar o leitor ou a conexão.To avoid this, make sure that you call Cancel before closing the reader or connection.

Aplica-se a