Abrufen in Konsolenanwendungen
Mithilfe von asynchronen Vorgängen in ADO.NET können Sie zeitaufwendige Datenbankvorgänge auf einem Thread initiieren, während andere Tasks auf einem weiteren Thread ausgeführt werden. In den meisten Szenarios erreichen Sie jedoch irgendwann einen Punkt, an dem die Anwendung angehalten werden sollte, bis der Datenbankvorgang beendet ist. Dann ist es hilfreich, den asynchronen Vorgang abzurufen, um zu ermitteln, ob der Vorgang abgeschlossen wurde.
Dafür können Sie die Eigenschaft IsCompleted verwenden.
Beispiel
Mit der folgenden Konsolenanwendung werden Daten innerhalb der AdventureWorks-Beispieldatenbank unter Verwendung eines asynchronen Vorgangs aktualisiert. In diesem Beispiel wird eine WAITFOR-Anweisung in den Befehlstext eingefügt, um einen Prozess mit langer Laufzeit zu emulieren. Normalerweise ist es nicht wünschenswert, dass Befehle langsamer ausgeführt werden, aber in diesem Fall kann dadurch das asynchrone Verhalten besser veranschaulicht werden.
Imports System
Imports System.Data.SqlClient
Module Module1
Sub Main()
' The WAITFOR statement simply adds enough time to prove the
' asynchronous nature of the command.
Dim commandText As String = _
"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()
End Sub
Private Sub RunCommandAsynchronously( _
ByVal commandText As String, ByVal connectionString As String)
' 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 connection As New SqlConnection(connectionString)
Try
Dim count As Integer = 0
Dim command As New SqlCommand(commandText, connection)
connection.Open()
Dim result As IAsyncResult = _
command.BeginExecuteNonQuery()
While Not 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.
Threading.Thread.Sleep(100)
count += 1
End While
Console.WriteLine( _
"Command complete. Affected {0} rows.", _
command.EndExecuteNonQuery(result))
Catch ex As SqlException
Console.WriteLine("Error ({0}): {1}", _
ex.Number, ex.Message)
Catch ex As InvalidOperationException
Console.WriteLine("Error: {0}", ex.Message)
Catch ex As Exception
' You might want to pass these errors
' back out to the caller.
Console.WriteLine("Error: {0}", ex.Message)
End Try
End Using
End Sub
Private Function GetConnectionString() As String
' 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 "..." & _
"Asynchronous Processing=true"
End Function
End Module
using System;
using System.Data;
using System.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 "..." + "Asynchronous Processing=true";
}
}