使用 ADO.NET 中的异步操作，可以在一个线程上启动耗时的数据库操作，同时在另一个线程上执行其他任务。 但在大多数情况下，最终会遇到这样的情况：在数据库操作完成之前，应用程序不应继续运行。 对于这种情况，一个有用的方法是轮询异步操作以确定操作是否已完成。
可以使用 IsCompleted 属性来确定操作是否已完成。
示例
以下控制台应用程序更新 AdventureWorks 示例数据库中的数据，异步完成其任务。 为了模拟长时间运行的进程，此示例在命令文本中插入一个 WAITFOR 语句。 通常，你不会尝试使命令运行速度变慢，但是在这种情况下，这样做可以更轻松地演示异步行为。
using System;
using System.Data;
using Microsoft.Data.SqlClient;
class Class1
{
[STAThread]
static void Main()
{
// The WAITFOR statement simply adds enough time to
// prove the asynchronous nature of the command.
string commandText =
"UPDATE Production.Product SET ReorderPoint = " +
"ReorderPoint + 1 " +
"WHERE ReorderPoint Is Not Null;" +
"WAITFOR DELAY '0:0:3';" +
"UPDATE Production.Product SET ReorderPoint = " +
"ReorderPoint - 1 " +
"WHERE ReorderPoint Is Not Null";
RunCommandAsynchronously(
commandText, GetConnectionString());
Console.WriteLine("Press Enter to continue.");
Console.ReadLine();
}
private static void RunCommandAsynchronously(
string commandText, string connectionString)
{
// Given command text and connection string, asynchronously
// execute the specified command against the connection.
// For this example, the code displays an indicator as it's
// working, verifying the asynchronous behavior.
using (SqlConnection connection =
new SqlConnection(connectionString))
{
try
{
int count = 0;
SqlCommand command =
new SqlCommand(commandText, connection);
connection.Open();
IAsyncResult result =
command.BeginExecuteNonQuery();
while (!result.IsCompleted)
{
Console.WriteLine(
"Waiting ({0})", count++);
// Wait for 1/10 second, so the counter
// doesn't consume all available
// resources on the main thread.
System.Threading.Thread.Sleep(100);
}
Console.WriteLine(
"Command complete. Affected {0} rows.",
command.EndExecuteNonQuery(result));
}
catch (SqlException ex)
{
Console.WriteLine("Error ({0}): {1}",
ex.Number, ex.Message);
}
catch (InvalidOperationException ex)
{
Console.WriteLine("Error: {0}", ex.Message);
}
catch (Exception ex)
{
// You might want to pass these errors
// back out to the caller.
Console.WriteLine("Error: {0}", ex.Message);
}
}
}
private static string GetConnectionString()
{
// To avoid storing the connection string in your code,
// you can retrieve it from a configuration file.
// If you have not included "Asynchronous Processing=true"
// in the connection string, the command will not be able
// to execute asynchronously.
return "Data Source=(local);Integrated Security=SSPI;" +
"Initial Catalog=AdventureWorks; " +
"Asynchronous Processing=true";
}
}