SqlCommand.Cancel 方法

定义

尝试取消 的执行 SqlCommand

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

示例

下面的示例演示 Cancel 方法的用法。

// <Snippet1>
using System;
using System.Data;
using Microsoft.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";
    }
}
// </Snippet1>

注解

如果没有要取消的命令,则不会有任何反应。 但是,如果有正在执行的命令,则即使取消尝试失败,也不会生成异常。

在某些极少数情况下,如果调用 ExecuteReader,则在调用 Close 之前Cancel隐式或显式调用 () ,然后调用 Cancel,取消命令将不会发送到SQL Server并且结果集可以在调用 Close后继续流式传输。 若要避免这种情况,请确保在关闭读取器或连接之前调用 Cancel

适用于