SqlCommand.BeginExecuteReader Metodo

Definizione

Avvia l'esecuzione asincrona dell'istruzione Transact-SQL o della stored procedure descritta da SqlCommand e recupera uno o più set di risultati dal server.Initiates the asynchronous execution of the Transact-SQL statement or stored procedure that is described by this SqlCommand, and retrieves one or more result sets from the server.

Overload

BeginExecuteReader()

Avvia l'esecuzione asincrona dell'istruzione Transact-SQL o della stored procedure descritta da SqlCommand e recupera uno o più set di risultati dal server.Initiates the asynchronous execution of the Transact-SQL statement or stored procedure that is described by this SqlCommand, and retrieves one or more result sets from the server.

BeginExecuteReader(CommandBehavior)

Avvia l'esecuzione asincrona dell'istruzione Transact-SQL o della stored procedure descritta dall'oggetto SqlCommand usando uno dei valori CommandBehavior.Initiates the asynchronous execution of the Transact-SQL statement or stored procedure that is described by this SqlCommand using one of the CommandBehavior values.

BeginExecuteReader(AsyncCallback, Object)

Avvia l'esecuzione asincrona dell'istruzione Transact-SQL o della stored procedure descritta dall'oggetto SqlCommand e recupera uno o più set di risultati dal server, in base alla routine di callback e alle informazioni sullo stato.Initiates the asynchronous execution of the Transact-SQL statement or stored procedure that is described by this SqlCommand and retrieves one or more result sets from the server, given a callback procedure and state information.

BeginExecuteReader(AsyncCallback, Object, CommandBehavior)

Avvia l'esecuzione asincrona dell'istruzione o della stored procedure Transact-SQL descritta da SqlCommand, usando uno dei valori di CommandBehavior e recuperando uno o più set di risultati dal server, in base a una routine di callback e alle informazioni sullo stato.Initiates the asynchronous execution of the Transact-SQL statement or stored procedure that is described by this SqlCommand, using one of the CommandBehavior values, and retrieving one or more result sets from the server, given a callback procedure and state information.

BeginExecuteReader()

Avvia l'esecuzione asincrona dell'istruzione Transact-SQL o della stored procedure descritta da SqlCommand e recupera uno o più set di risultati dal server.Initiates the asynchronous execution of the Transact-SQL statement or stored procedure that is described by this SqlCommand, and retrieves one or more result sets from the server.

public:
 IAsyncResult ^ BeginExecuteReader();
public IAsyncResult BeginExecuteReader ();
member this.BeginExecuteReader : unit -> IAsyncResult
Public Function BeginExecuteReader () As IAsyncResult

Restituisce

IAsyncResult

Oggetto IAsyncResult che può essere usato per eseguire il polling, attendere i risultati o entrambe le cose. Questo valore è necessario anche per chiamare il metodo EndExecuteReader(IAsyncResult), che restituisce un'istanza SqlDataReader utilizzabile per recuperare le righe restituite.An IAsyncResult that can be used to poll or wait for results, or both; this value is also needed when invoking EndExecuteReader(IAsyncResult), which returns a SqlDataReader instance that can be used to retrieve the returned rows.

Eccezioni

È stato usato un valore SqlDbType diverso da Binary o VarBinary quando Value era impostato su Stream.A SqlDbType other than Binary or VarBinary was used when Value was set to Stream. Per altre informazioni sul flusso, vedere Supporto del flusso SqlClient.For more information about streaming, see SqlClient Streaming Support.

-oppure--or-

È stato usato un valore SqlDbType diverso da Char, NChar, NVarChar, VarChar o Xml quando Value era impostato su TextReader.A SqlDbType other than Char, NChar, NVarChar, VarChar, or Xml was used when Value was set to TextReader.

-oppure--or-

È stato usato un valore SqlDbType diverso da Xml quando Value era impostato su XmlReader.A SqlDbType other than Xml was used when Value was set to XmlReader.

Qualsiasi errore che si è verificato durante l'esecuzione del testo del comando.Any error that occurred while executing the command text.

-oppure--or-

Si è verificato un timeout durante un'operazione di flusso.A timeout occurred during a streaming operation. Per altre informazioni sul flusso, vedere Supporto del flusso SqlClient.For more information about streaming, see SqlClient Streaming Support.

La coppia nome/valore "Asynchronous Processing=true" non è stata inclusa nella stringa di connessione che definisce la connessione per SqlCommand.The name/value pair "Asynchronous Processing=true" was not included within the connection string defining the connection for this SqlCommand.

-oppure--or-

L'elemento SqlConnection chiuso o eliminato durante l'operazione di flusso.The SqlConnection closed or dropped during a streaming operation. Per altre informazioni sul flusso, vedere Supporto del flusso SqlClient.For more information about streaming, see SqlClient Streaming Support.

Errore nell'oggetto Stream, XmlReader o TextReader durante un'operazione di flusso.An error occurred in a Stream, XmlReader or TextReader object during a streaming operation. Per altre informazioni sul flusso, vedere Supporto del flusso SqlClient.For more information about streaming, see SqlClient Streaming Support.

L'oggetto Stream, XmlReader o TextReader è stato chiuso durante l'operazione di flusso.The Stream, XmlReader or TextReader object was closed during a streaming operation. Per altre informazioni sul flusso, vedere Supporto del flusso SqlClient.For more information about streaming, see SqlClient Streaming Support.

Esempio

La seguente applicazione console avvia il processo di recupero asincrono di un lettore dati.The following console application starts the process of retrieving a data reader asynchronously. Durante l'attesa dei risultati, questa semplice applicazione si trova in un ciclo, esaminando il IsCompleted valore della proprietà.While waiting for the results, this simple application sits in a loop, investigating the IsCompleted property value. Non appena il processo è stato completato, il codice recupera l'oggetto SqlDataReader e ne Visualizza il contenuto.As soon as the process has completed, the code retrieves the SqlDataReader and displays its contents.

using System.Data.SqlClient;

class Class1
{
    static void Main()
    {
        // This is a simple example that demonstrates the usage of the
        // BeginExecuteReader functionality
        // The WAITFOR statement simply adds enough time to prove the
        // asynchronous nature of the command.
        string commandText =
            "WAITFOR DELAY '00:00:03';" +
            "SELECT LastName, FirstName FROM Person.Contact " +
            "WHERE LastName LIKE 'M%'";

        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 is working, verifying the
        // asynchronous behavior.
        using (SqlConnection connection = new SqlConnection(connectionString))
        {
            try
            {
                SqlCommand command = new SqlCommand(commandText, connection);

                connection.Open();
                IAsyncResult result = command.BeginExecuteReader();

                // Although it is not necessary, the following code
                // displays a counter in the console window, indicating that
                // the main thread is not blocked while awaiting the command
                // results.
                int count = 0;
                while (!result.IsCompleted)
                {
                    count += 1;
                    Console.WriteLine("Waiting ({0})", count);
                    // Wait for 1/10 second, so the counter
                    // does not consume all available resources
                    // on the main thread.
                    System.Threading.Thread.Sleep(100);
                }

                using (SqlDataReader reader = command.EndExecuteReader(result))
                {
                    DisplayResults(reader);
                }
            }
            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 void DisplayResults(SqlDataReader reader)
    {
        // Display the data within the reader.
        while (reader.Read())
        {
            // Display all the columns.
            for (int i = 0; i < reader.FieldCount; i++)
                Console.Write("{0} ", reader.GetValue(i));
            Console.WriteLine();
        }
    }

    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 is not able
        // to execute asynchronously.
        return "Data Source=(local);Integrated Security=true;" +
            "Initial Catalog=AdventureWorks; Asynchronous Processing=true";
    }
}
Imports System.Data.SqlClient

Module Module1
    Sub Main()
        ' This is a simple example that demonstrates the usage of the 
        ' BeginExecuteReader functionality.
        ' The WAITFOR statement simply adds enough time to prove the 
        ' asynchronous nature of the command.
        Dim commandText As String = _
         "WAITFOR DELAY '00:00:03';" & _
         "SELECT LastName, FirstName FROM Person.Contact " & _
         "WHERE LastName LIKE 'M%'"

        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 is working, verifying the 
        ' asynchronous behavior. 
        Using connection As New SqlConnection(connectionString)
            Try
                Dim command As New SqlCommand(commandText, connection)

                connection.Open()
                Dim result As IAsyncResult = command.BeginExecuteReader()

                ' Although it is not necessary, the following procedure
                ' displays a counter in the console window, indicating that 
                ' the main thread is not blocked while awaiting the command 
                ' results.
                Dim count As Integer
                While Not result.IsCompleted
                    count += 1
                    Console.WriteLine("Waiting ({0})", count)
                    ' Wait for 1/10 second, so the counter
                    ' does not consume all available resources 
                    ' on the main thread.
                    Threading.Thread.Sleep(100)
                End While

                ' Once the IAsyncResult object signals that it is done
                ' waiting for results, you can retrieve the results.
                Using reader As SqlDataReader = command.EndExecuteReader(result)
                    DisplayResults(reader)
                End Using
            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 Sub DisplayResults(ByVal reader As SqlDataReader)
        ' Display the data within the reader.
        While reader.Read()
            ' Display all the columns.
            For i As Integer = 0 To reader.FieldCount - 1
                Console.Write("{0} ", reader.GetValue(i))
            Next
            Console.WriteLine()
        End While
    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 is not able
        ' to execute asynchronously.
        Return "Data Source=(local);Integrated Security=true;" & _
          "Initial Catalog=AdventureWorks; Asynchronous Processing=true"
    End Function
End Module

Commenti

Il BeginExecuteReader metodo avvia il processo di esecuzione asincrona di un'istruzione Transact-SQL o stored procedure che restituisce righe, in modo che le altre attività possano essere eseguite simultaneamente durante l'esecuzione dell'istruzione.The BeginExecuteReader method starts the process of asynchronously executing a Transact-SQL statement or stored procedure that returns rows, so that other tasks can run concurrently while the statement is executing. Al termine dell'istruzione, gli sviluppatori devono chiamare il EndExecuteReader metodo per terminare l'operazione e recuperare l'oggetto SqlDataReader restituito dal comando.When the statement has completed, developers must call the EndExecuteReader method to finish the operation and retrieve the SqlDataReader returned by the command. Il BeginExecuteReader metodo restituisce immediatamente un risultato, ma fino a quando il codice EndExecuteReader non esegue la chiamata al metodo corrispondente, non deve eseguire altre chiamate che avviano un'esecuzione sincrona o asincrona sullo stesso SqlCommand oggetto.The BeginExecuteReader method returns immediately, but until the code executes the corresponding EndExecuteReader method call, it must not execute any other calls that start a synchronous or asynchronous execution against the same SqlCommand object. La chiamata di EndExecuteReader prima del completamento dell'esecuzione del comando comporta il SqlCommand blocco dell'oggetto fino al termine dell'esecuzione.Calling the EndExecuteReader before the command's execution is completed causes the SqlCommand object to block until the execution is finished.

Si noti che il testo del comando e i parametri vengono inviati al server in modo sincrono.Note that the command text and parameters are sent to the server synchronously. Se vengono inviati un comando di grandi dimensioni o molti parametri, questo metodo potrebbe bloccarsi durante le Scritture.If a large command or many parameters are sent, this method may block during writes. Una volta inviato il comando, il metodo viene restituito immediatamente senza attendere una risposta dal server, ovvero le letture sono asincrone.After the command is sent, the method returns immediately without waiting for an answer from the server--that is, reads are asynchronous. Anche se l'esecuzione del comando è asincrona, il recupero del valore è ancora sincrono.Although command execution is asynchronous, value fetching is still synchronous. Ciò significa che le chiamate a Read possono bloccarsi se sono necessari più dati e l'operazione di lettura della rete sottostante si blocca.This means that calls to Read may block if more data is required and the underlying network's read operation blocks.

Poiché questo overload non supporta una routine di callback, gli sviluppatori devono eseguire il polling per determinare se il comando è stato completato, usando la IsCompleted proprietà dell'oggetto IAsyncResult restituito dal BeginExecuteReader metodo oppure attendere il completamento di uno o più comandi usando la AsyncWaitHandle proprietà dell'oggetto restituito IAsyncResult .Because this overload does not support a callback procedure, developers must either poll to determine whether the command has completed, using the IsCompleted property of the IAsyncResult returned by the BeginExecuteReader method; or wait for the completion of one or more commands using the AsyncWaitHandle property of the returned IAsyncResult.

Se si usa ExecuteReader o BeginExecuteReader per accedere ai dati xml, SQL Server restituirà tutti i risultati XML di lunghezza superiore a 2.033 caratteri in più righe di 2.033 caratteri.If you use ExecuteReader or BeginExecuteReader to access XML data, SQL Server will return any XML results greater than 2,033 characters in length in multiple rows of 2,033 characters each. Per evitare questo comportamento, utilizzare ExecuteXmlReader o BeginExecuteXmlReader per leggere query for XML.To avoid this behavior, use ExecuteXmlReader or BeginExecuteXmlReader to read FOR XML queries.

Questo metodo ignora la CommandTimeout Proprietà.This method ignores the CommandTimeout property.

Vedi anche

Si applica a

Prodotto Presentazione

BeginExecuteReader(CommandBehavior)

Avvia l'esecuzione asincrona dell'istruzione Transact-SQL o della stored procedure descritta dall'oggetto SqlCommand usando uno dei valori CommandBehavior.Initiates the asynchronous execution of the Transact-SQL statement or stored procedure that is described by this SqlCommand using one of the CommandBehavior values.

public:
 IAsyncResult ^ BeginExecuteReader(System::Data::CommandBehavior behavior);
public IAsyncResult BeginExecuteReader (System.Data.CommandBehavior behavior);
member this.BeginExecuteReader : System.Data.CommandBehavior -> IAsyncResult
Public Function BeginExecuteReader (behavior As CommandBehavior) As IAsyncResult

Parametri

behavior
CommandBehavior

Uno dei valori di CommandBehavior che indica le opzioni per l'esecuzione dell'istruzione e il recupero dei dati.One of the CommandBehavior values, indicating options for statement execution and data retrieval.

Restituisce

IAsyncResult

Oggetto IAsyncResult che può essere usato per eseguire il polling, attendere i risultati o entrambe le cose. Questo valore è necessario anche per chiamare il metodo EndExecuteReader(IAsyncResult), che restituisce un'istanza SqlDataReader utilizzabile per recuperare le righe restituite.An IAsyncResult that can be used to poll, wait for results, or both; this value is also needed when invoking EndExecuteReader(IAsyncResult), which returns a SqlDataReader instance that can be used to retrieve the returned rows.

Eccezioni

È stato usato un valore SqlDbType diverso da Binary o VarBinary quando Value era impostato su Stream.A SqlDbType other than Binary or VarBinary was used when Value was set to Stream. Per altre informazioni sul flusso, vedere Supporto del flusso SqlClient.For more information about streaming, see SqlClient Streaming Support.

-oppure--or-

È stato usato un valore SqlDbType diverso da Char, NChar, NVarChar, VarChar o Xml quando Value era impostato su TextReader.A SqlDbType other than Char, NChar, NVarChar, VarChar, or Xml was used when Value was set to TextReader.

-oppure--or-

È stato usato un valore SqlDbType diverso da Xml quando Value era impostato su XmlReader.A SqlDbType other than Xml was used when Value was set to XmlReader.

Qualsiasi errore che si è verificato durante l'esecuzione del testo del comando.Any error that occurred while executing the command text.

-oppure--or-

Si è verificato un timeout durante un'operazione di flusso.A timeout occurred during a streaming operation. Per altre informazioni sul flusso, vedere Supporto del flusso SqlClient.For more information about streaming, see SqlClient Streaming Support.

La coppia nome/valore "Asynchronous Processing=true" non è stata inclusa nella stringa di connessione che definisce la connessione per SqlCommand.The name/value pair "Asynchronous Processing=true" was not included within the connection string defining the connection for this SqlCommand.

-oppure--or-

L'elemento SqlConnection chiuso o eliminato durante l'operazione di flusso.The SqlConnection closed or dropped during a streaming operation. Per altre informazioni sul flusso, vedere Supporto del flusso SqlClient.For more information about streaming, see SqlClient Streaming Support.

Errore nell'oggetto Stream, XmlReader o TextReader durante un'operazione di flusso.An error occurred in a Stream, XmlReader or TextReader object during a streaming operation. Per altre informazioni sul flusso, vedere Supporto del flusso SqlClient.For more information about streaming, see SqlClient Streaming Support.

L'oggetto Stream, XmlReader o TextReader è stato chiuso durante l'operazione di flusso.The Stream, XmlReader or TextReader object was closed during a streaming operation. Per altre informazioni sul flusso, vedere Supporto del flusso SqlClient.For more information about streaming, see SqlClient Streaming Support.

Esempio

La seguente applicazione console avvia il processo di recupero asincrono di un lettore dati.The following console application starts the process of retrieving a data reader asynchronously. Durante l'attesa dei risultati, questa semplice applicazione si trova in un ciclo, esaminando il IsCompleted valore della proprietà.While waiting for the results, this simple application sits in a loop, investigating the IsCompleted property value. Al termine del processo, il codice recupera l'oggetto SqlDataReader e ne Visualizza il contenuto.Once the process has completed, the code retrieves the SqlDataReader and displays its contents.

In questo esempio vengono anche passati i CommandBehavior.CloseConnection CommandBehavior.SingleRow valori e nel parametro behavior, causando la chiusura della connessione con l'oggetto restituito SqlDataReader , e per ottimizzare il risultato di una singola riga.This example also passes the CommandBehavior.CloseConnection and CommandBehavior.SingleRow values in the behavior parameter, causing the connection to be closed with the returned SqlDataReader is closed, and to optimize for a single row result.

using System.Data.SqlClient;
class Class1
{
    static void Main()
    {
        // This example is not terribly useful, but it proves a point.
        // The WAITFOR statement simply adds enough time to prove the
        // asynchronous nature of the command.
        string commandText = "WAITFOR DELAY '00:00:03';" +
            "SELECT ProductID, Name FROM Production.Product WHERE ListPrice < 100";

        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 is working, verifying the
        // asynchronous behavior.

        try
        {
            // The code does not need to handle closing the connection explicitly--
            // the use of the CommandBehavior.CloseConnection option takes care
            // of that for you.
            SqlConnection connection = new SqlConnection(connectionString);
            SqlCommand command = new SqlCommand(commandText, connection);

            connection.Open();
            IAsyncResult result = command.BeginExecuteReader(
                CommandBehavior.CloseConnection);

            // Although it is not necessary, the following code
            // displays a counter in the console window, indicating that
            // the main thread is not blocked while awaiting the command
            // results.
            int count = 0;
            while (!result.IsCompleted)
            {
                Console.WriteLine("Waiting ({0})", count++);
                // Wait for 1/10 second, so the counter
                // does not consume all available resources
                // on the main thread.
                System.Threading.Thread.Sleep(100);
            }

            using (SqlDataReader reader = command.EndExecuteReader(result))
            {
                DisplayResults(reader);
            }
        }
        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 void DisplayResults(SqlDataReader reader)
    {
        // Display the data within the reader.
        while (reader.Read())
        {
            // Display all the columns.
            for (int i = 0; i < reader.FieldCount; i++)
            {
                Console.Write("{0}\t", reader.GetValue(i));
            }
            Console.WriteLine();
        }
    }

    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 is not able
        // to execute asynchronously.
        return "Data Source=(local);Integrated Security=true;" +
            "Initial Catalog=AdventureWorks; Asynchronous Processing=true";
    }
}
Imports System.Data.SqlClient

Module Module1
    Sub Main()
        ' This example is not terribly useful, but it proves a point.
        ' The WAITFOR statement simply adds enough time to prove the 
        ' asynchronous nature of the command.
        Dim commandText As String = _
         "WAITFOR DELAY '00:00:03';" & _
         "SELECT ProductID, Name FROM Production.Product WHERE ListPrice < 100"

        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 is working, verifying the 
        ' asynchronous behavior. 
        Try
            ' The code does not need to handle closing the connection explicitly--
            ' the use of the CommandBehavior.CloseConnection option takes care
            ' of that for you. 
            Dim connection As New SqlConnection(connectionString)
            Dim command As New SqlCommand(commandText, connection)

            connection.Open()
            Dim result As IAsyncResult = _
              command.BeginExecuteReader(CommandBehavior.CloseConnection)

            ' Although it is not necessary, the following code
            ' displays a counter in the console window, indicating that 
            ' the main thread is not blocked while awaiting the command 
            ' results.
            Dim count As Integer = 0
            While Not result.IsCompleted
                count += 1
                Console.WriteLine("Waiting ({0})", count)
                ' Wait for 1/10 second, so the counter
                ' does not consume all available resources 
                ' on the main thread.
                Threading.Thread.Sleep(100)
            End While

            ' The "using" statement closes the SqlDataReader when it is 
            ' done executing.
            Using reader As SqlDataReader = command.EndExecuteReader(result)
                DisplayResults(reader)
            End Using
        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 Sub

    Private Sub DisplayResults(ByVal reader As SqlDataReader)
        ' Display the data within the reader.
        While reader.Read()
            ' Display all the columns. 
            For i As Integer = 0 To reader.FieldCount - 1
                Console.Write("{0} ", reader.GetValue(i))
            Next
            Console.WriteLine()
        End While
    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 is not able
        ' to execute asynchronously.
        Return "Data Source=(local);Integrated Security=true;" & _
          "Initial Catalog=AdventureWorks; Asynchronous Processing=true"
    End Function
End Module

Commenti

Il BeginExecuteReader metodo avvia il processo di esecuzione asincrona di un'istruzione Transact-SQL o stored procedure che restituisce righe, in modo che le altre attività possano essere eseguite simultaneamente durante l'esecuzione dell'istruzione.The BeginExecuteReader method starts the process of asynchronously executing a Transact-SQL statement or stored procedure that returns rows, so that other tasks can run concurrently while the statement is executing. Al termine dell'istruzione, gli sviluppatori devono chiamare il EndExecuteReader metodo per terminare l'operazione e recuperare l'oggetto SqlDataReader restituito dal comando.When the statement has completed, developers must call the EndExecuteReader method to finish the operation and retrieve the SqlDataReader returned by the command. Il BeginExecuteReader metodo restituisce immediatamente un risultato, ma fino a quando il codice EndExecuteReader non esegue la chiamata al metodo corrispondente, non deve eseguire altre chiamate che avviano un'esecuzione sincrona o asincrona sullo stesso SqlCommand oggetto.The BeginExecuteReader method returns immediately, but until the code executes the corresponding EndExecuteReader method call, it must not execute any other calls that start a synchronous or asynchronous execution against the same SqlCommand object. La chiamata di EndExecuteReader prima del completamento dell'esecuzione del comando comporta il SqlCommand blocco dell'oggetto fino al termine dell'esecuzione.Calling the EndExecuteReader before the command's execution is completed causes the SqlCommand object to block until the execution is finished.

Il behavior parametro consente di specificare le opzioni che controllano il comportamento del comando e la relativa connessione.The behavior parameter lets you specify options that control the behavior of the command and its connection. Questi valori possono essere combinati insieme (usando l'operatore del linguaggio di programmazione OR ); in genere, gli sviluppatori usano il CommandBehavior.CloseConnection valore per assicurarsi che la connessione venga chiusa dal runtime quando SqlDataReader viene chiuso.These values can be combined together (using the programming language's OR operator); generally, developers use the CommandBehavior.CloseConnection value to make sure that the connection is closed by the runtime when the SqlDataReader is closed.

Si noti che il testo del comando e i parametri vengono inviati al server in modo sincrono.Note that the command text and parameters are sent to the server synchronously. Se vengono inviati un comando di grandi dimensioni o molti parametri, questo metodo potrebbe bloccarsi durante le Scritture.If a large command or many parameters are sent, this method may block during writes. Una volta inviato il comando, il metodo viene restituito immediatamente senza attendere una risposta dal server, ovvero le letture sono asincrone.After the command is sent, the method returns immediately without waiting for an answer from the server--that is, reads are asynchronous. Anche se l'esecuzione del comando è asincrona, il recupero del valore è ancora sincrono.Although command execution is asynchronous, value fetching is still synchronous. Ciò significa che le chiamate a Read possono bloccarsi se sono necessari più dati e l'operazione di lettura della rete sottostante si blocca.This means that calls to Read may block if more data is required and the underlying network's read operation blocks.

Poiché questo overload non supporta una routine di callback, gli sviluppatori devono eseguire il polling per determinare se il comando è stato completato, usando la IsCompleted proprietà dell'oggetto IAsyncResult restituito dal BeginExecuteNonQuery metodo oppure attendere il completamento di uno o più comandi usando la AsyncWaitHandle proprietà dell'oggetto restituito IAsyncResult .Because this overload does not support a callback procedure, developers must either poll to determine whether the command has completed, using the IsCompleted property of the IAsyncResult returned by the BeginExecuteNonQuery method; or wait for the completion of one or more commands using the AsyncWaitHandle property of the returned IAsyncResult.

Se si usa ExecuteReader o BeginExecuteReader per accedere ai dati xml, SQL Server restituisce tutti i risultati XML di lunghezza superiore a 2.033 caratteri in più righe di 2.033 caratteri.If you use ExecuteReader or BeginExecuteReader to access XML data, SQL Server returns any XML results greater than 2,033 characters in length in multiple rows of 2,033 characters each. Per evitare questo comportamento, utilizzare ExecuteXmlReader o BeginExecuteXmlReader per leggere query for XML.To avoid this behavior, use ExecuteXmlReader or BeginExecuteXmlReader to read FOR XML queries.

Questo metodo ignora la CommandTimeout Proprietà.This method ignores the CommandTimeout property.

Vedi anche

Si applica a

Prodotto Presentazione

BeginExecuteReader(AsyncCallback, Object)

Avvia l'esecuzione asincrona dell'istruzione Transact-SQL o della stored procedure descritta dall'oggetto SqlCommand e recupera uno o più set di risultati dal server, in base alla routine di callback e alle informazioni sullo stato.Initiates the asynchronous execution of the Transact-SQL statement or stored procedure that is described by this SqlCommand and retrieves one or more result sets from the server, given a callback procedure and state information.

public:
 IAsyncResult ^ BeginExecuteReader(AsyncCallback ^ callback, System::Object ^ stateObject);
public IAsyncResult BeginExecuteReader (AsyncCallback callback, object stateObject);
member this.BeginExecuteReader : AsyncCallback * obj -> IAsyncResult
Public Function BeginExecuteReader (callback As AsyncCallback, stateObject As Object) As IAsyncResult

Parametri

callback
AsyncCallback

Delegato AsyncCallback richiamato al termine dell'esecuzione del comando.An AsyncCallback delegate that is invoked when the command's execution has completed. Passare null (Nothing in Microsoft Visual Basic) per indicare che non è necessario alcun callback.Pass null (Nothing in Microsoft Visual Basic) to indicate that no callback is required.

stateObject
Object

Oggetto di stato definito dall'utente e passato alla routine di callback.A user-defined state object that is passed to the callback procedure. Recuperare questo oggetto dalla routine di callback usando la proprietà AsyncState.Retrieve this object from within the callback procedure using the AsyncState property.

Restituisce

IAsyncResult

Oggetto IAsyncResult che può essere usato per eseguire il polling, attendere i risultati o entrambe le cose. Questo valore è necessario anche per chiamare il metodo EndExecuteReader(IAsyncResult), che restituisce un'istanza di SqlDataReader che può essere usata per recuperare le righe restituite.An IAsyncResult that can be used to poll, wait for results, or both; this value is also needed when invoking EndExecuteReader(IAsyncResult), which returns a SqlDataReader instance which can be used to retrieve the returned rows.

Eccezioni

È stato usato un valore SqlDbType diverso da Binary o VarBinary quando Value era impostato su Stream.A SqlDbType other than Binary or VarBinary was used when Value was set to Stream. Per altre informazioni sul flusso, vedere Supporto del flusso SqlClient.For more information about streaming, see SqlClient Streaming Support.

-oppure--or-

È stato usato un valore SqlDbType diverso da Char, NChar, NVarChar, VarChar o Xml quando Value era impostato su TextReader.A SqlDbType other than Char, NChar, NVarChar, VarChar, or Xml was used when Value was set to TextReader.

-oppure--or-

È stato usato un valore SqlDbType diverso da Xml quando Value era impostato su XmlReader.A SqlDbType other than Xml was used when Value was set to XmlReader.

Qualsiasi errore che si è verificato durante l'esecuzione del testo del comando.Any error that occurred while executing the command text.

-oppure--or-

Si è verificato un timeout durante un'operazione di flusso.A timeout occurred during a streaming operation. Per altre informazioni sul flusso, vedere Supporto del flusso SqlClient.For more information about streaming, see SqlClient Streaming Support.

La coppia nome/valore "Asynchronous Processing=true" non è stata inclusa nella stringa di connessione che definisce la connessione per SqlCommand.The name/value pair "Asynchronous Processing=true" was not included within the connection string defining the connection for this SqlCommand.

-oppure--or-

L'elemento SqlConnection chiuso o eliminato durante l'operazione di flusso.The SqlConnection closed or dropped during a streaming operation. Per altre informazioni sul flusso, vedere Supporto del flusso SqlClient.For more information about streaming, see SqlClient Streaming Support.

Errore nell'oggetto Stream, XmlReader o TextReader durante un'operazione di flusso.An error occurred in a Stream, XmlReader or TextReader object during a streaming operation. Per altre informazioni sul flusso, vedere Supporto del flusso SqlClient.For more information about streaming, see SqlClient Streaming Support.

L'oggetto Stream, XmlReader o TextReader è stato chiuso durante l'operazione di flusso.The Stream, XmlReader or TextReader object was closed during a streaming operation. Per altre informazioni sul flusso, vedere Supporto del flusso SqlClient.For more information about streaming, see SqlClient Streaming Support.

Esempio

Nell'applicazione Windows seguente viene illustrato l'uso del metodo BeginExecuteReader, eseguendo un'istruzione Transact-SQL che include un ritardo di pochi secondi (emulando un comando con esecuzione prolungata).The following Windows application demonstrates the use of the BeginExecuteReader method, executing a Transact-SQL statement that includes a delay of a few seconds (emulating a long-running command). Poiché l'esempio esegue il comando in modo asincrono, il form rimane reattivo mentre è in attesa dei risultati.Because the sample executes the command asynchronously, the form remains responsive while awaiting the results. Questo esempio passa l'oggetto in esecuzione SqlCommand come stateObject parametro; in questo modo è semplice recuperare l' SqlCommand oggetto dall'interno della routine di callback, in modo che il codice possa chiamare il EndExecuteReader metodo corrispondente alla chiamata iniziale a BeginExecuteReader .This example passes the executing SqlCommand object as the stateObject parameter; doing so makes it simple to retrieve the SqlCommand object from within the callback procedure, so that the code can call the EndExecuteReader method corresponding to the initial call to BeginExecuteReader.

In questo esempio vengono illustrate molte tecniche importanti.This example demonstrates many important techniques. Ciò include la chiamata a un metodo che interagisce con il form da un thread separato.This includes calling a method that interacts with the form from a separate thread. In questo esempio viene inoltre illustrato come impedire agli utenti di eseguire un comando più volte simultaneamente e come è necessario assicurarsi che il form non venga chiuso prima che venga chiamata la procedura di callback.In addition, this example demonstrates how you must block users from executing a command multiple times concurrently, and how you must make sure that the form does not close before the callback procedure is called.

Per impostare questo esempio, creare una nuova applicazione Windows.To set up this example, create a new Windows application. Inserire un controllo Button , un DataGridView controllo e un Label controllo sul form (accettando il nome predefinito per ogni controllo).Put a Button control, a DataGridView control, and a Label control on the form (accepting the default name for each control). Aggiungere il codice seguente alla classe del form, modificando la stringa di connessione in base alle esigenze dell'ambiente.Add the following code to the form's class, modifying the connection string as needed for your environment.

using System.Data.SqlClient;

namespace Microsoft.AdoDotNet.CodeSamples
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        // Hook up the form's Load event handler (you can double-click on
        // the form's design surface in Visual Studio), and then add
        // this code to the form's class:

        // You need this delegate in order to fill the grid from
        // a thread other than the form's thread. See the HandleCallback
        // procedure for more information.
        private delegate void FillGridDelegate(SqlDataReader reader);

        // You need this delegate to update the status bar.
        private delegate void DisplayStatusDelegate(string Text);

        // This flag ensures that the user does not attempt
        // to restart the command or close the form while the
        // asynchronous command is executing.
        private bool isExecuting = false;

        // Because the overloaded version of BeginExecuteReader
        // demonstrated here does not allow you to have the connection
        // closed automatically, this example maintains the
        // connection object externally, so that it is available for closing.
        private SqlConnection connection = null;

        private void DisplayStatus(string Text)
        {
            this.label1.Text = Text;
        }

        private void FillGrid(SqlDataReader reader)
        {
            try
            {
                DataTable table = new DataTable();
                table.Load(reader);
                this.dataGridView1.DataSource = table;
                DisplayStatus("Ready");
            }
            catch (Exception ex)
            {
                // Because you are guaranteed this procedure
                // is running from within the form's thread,
                // it can directly interact with members of the form.
                DisplayStatus(string.Format("Ready (last attempt failed: {0})",
                    ex.Message));
            }
            finally
            {
                // Do not forget to close the connection, as well.
                if (reader != null)
                {
                    reader.Close();
                }
                if (connection != null)
                {
                    connection.Close();
                }
            }
        }

        private void HandleCallback(IAsyncResult result)
        {
            try
            {
                // Retrieve the original command object, passed
                // to this procedure in the AsyncState property
                // of the IAsyncResult parameter.
                SqlCommand command = (SqlCommand)result.AsyncState;
                SqlDataReader reader = command.EndExecuteReader(result);
                // You may not interact with the form and its contents
                // from a different thread, and this callback procedure
                // is all but guaranteed to be running from a different thread
                // than the form. Therefore you cannot simply call code that
                // fills the grid, like this:
                // FillGrid(reader);
                // Instead, you must call the procedure from the form's thread.
                // One simple way to accomplish this is to call the Invoke
                // method of the form, which calls the delegate you supply
                // from the form's thread.
                FillGridDelegate del = new FillGridDelegate(FillGrid);
                this.Invoke(del, reader);
                // Do not close the reader here, because it is being used in
                // a separate thread. Instead, have the procedure you have
                // called close the reader once it is done with it.
            }
            catch (Exception ex)
            {
                // Because you are now running code in a separate thread,
                // if you do not handle the exception here, none of your other
                // code catches the exception. Because there is none of
                // your code on the call stack in this thread, there is nothing
                // higher up the stack to catch the exception if you do not
                // handle it here. You can either log the exception or
                // invoke a delegate (as in the non-error case in this
                // example) to display the error on the form. In no case
                // can you simply display the error without executing a delegate
                // as in the try block here.
                // You can create the delegate instance as you
                // invoke it, like this:
                this.Invoke(new DisplayStatusDelegate(DisplayStatus),
                    "Error: " + ex.Message);
            }
            finally
            {
                isExecuting = false;
            }
        }

        private string GetConnectionString()
        {
            // To avoid storing the connection string in your code,
            // you can retrieve it from a configuration file.

            // If you do not include the Asynchronous Processing=true name/value pair,
            // you wo not be able to execute the command asynchronously.
            return "Data Source=(local);Integrated Security=true;" +
                "Initial Catalog=AdventureWorks; Asynchronous Processing=true";
        }

        private void button1_Click(object sender, System.EventArgs e)
        {
            if (isExecuting)
            {
                MessageBox.Show(this,
                    "Already executing. Please wait until the current query " +
                    "has completed.");
            }
            else
            {
                SqlCommand command = null;
                try
                {
                    DisplayStatus("Connecting...");
                    connection = new SqlConnection(GetConnectionString());
                    // To emulate a long-running query, wait for
                    // a few seconds before retrieving the real data.
                    command = new SqlCommand("WAITFOR DELAY '0:0:5';" +
                        "SELECT ProductID, Name, ListPrice, Weight FROM Production.Product",
                        connection);
                    connection.Open();

                    DisplayStatus("Executing...");
                    isExecuting = true;
                    // Although it is not required that you pass the
                    // SqlCommand object as the second parameter in the
                    // BeginExecuteReader call, doing so makes it easier
                    // to call EndExecuteReader in the callback procedure.
                    AsyncCallback callback = new AsyncCallback(HandleCallback);
                    command.BeginExecuteReader(callback, command);
                }
                catch (Exception ex)
                {
                    DisplayStatus("Error: " + ex.Message);
                    if (connection != null)
                    {
                        connection.Close();
                    }
                }
            }
        }

        private void Form1_Load(object sender, System.EventArgs e)
        {
            this.button1.Click += new System.EventHandler(this.button1_Click);
            this.FormClosing += new FormClosingEventHandler(Form1_FormClosing);
        }

        void Form1_FormClosing(object sender, FormClosingEventArgs e)
        {
            if (isExecuting)
            {
                MessageBox.Show(this, "Cannot close the form until " +
                    "the pending asynchronous command has completed. Please wait...");
                e.Cancel = true;
            }
        }
    }
}
Imports System.Data.SqlClient

Public Class Form1
    ' Add this code to the form's class:
    ' You need this delegate in order to fill the grid from
    ' a thread other than the form's thread. See the HandleCallback
    ' procedure for more information.
    Private Delegate Sub FillGridDelegate(ByVal reader As SqlDataReader)

    ' You need this delegate to update the status bar.
    Private Delegate Sub DisplayStatusDelegate(ByVal Text As String)

    ' This flag ensures that the user does not attempt
    ' to restart the command or close the form while the 
    ' asynchronous command is executing.
    Private isExecuting As Boolean

    ' Because the overloaded version of BeginExecuteReader
    ' demonstrated here does not allow you to have the connection
    ' closed automatically, this example maintains the 
    ' connection object externally, so that it is available for closing.
    Private connection As SqlConnection

    Private Sub DisplayStatus(ByVal Text As String)
        Me.Label1.Text = Text
    End Sub

    Private Sub FillGrid(ByVal reader As SqlDataReader)
        Try
            Dim table As New DataTable
            table.Load(reader)
            Me.DataGridView1.DataSource = table
            DisplayStatus("Ready")

        Catch ex As Exception
            ' Because you are guaranteed this procedure
            ' is running from within the form's thread,
            ' it can directly interact with members of the form.
            DisplayStatus(String.Format("Ready (last attempt failed: {0})", ex.Message))
        Finally
            ' Do not forget to close the connection, as well.
            If Not reader Is Nothing Then
                reader.Close()
            End If
            If Not connection Is Nothing Then
                connection.Close()
            End If
        End Try
    End Sub

    Private Sub HandleCallback(ByVal result As IAsyncResult)
        Try
            ' Retrieve the original command object, passed
            ' to this procedure in the AsyncState property
            ' of the IAsyncResult parameter.
            Dim command As SqlCommand = CType(result.AsyncState, SqlCommand)
            Dim reader As SqlDataReader = command.EndExecuteReader(result)

            ' You may not interact with the form and its contents
            ' from a different thread, and this callback procedure
            ' is all but guaranteed to be running from a different thread
            ' than the form. Therefore you cannot simply call code that 
            ' fills the grid, like this:
            ' FillGrid(reader)

            ' Instead, you must call the procedure from the form's thread.
            ' One simple way to accomplish this is to call the Invoke
            ' method of the form, which calls the delegate you supply
            ' from the form's thread. 
            Dim del As New FillGridDelegate(AddressOf FillGrid)
            Me.Invoke(del, reader)
            ' Do not close the reader here, because it is being used in 
            ' a separate thread. Instead, have the procedure you have
            ' called close the reader once it is done with it.

        Catch ex As Exception
            ' Because you are now running code in a separate thread, 
            ' if you do not handle the exception here, none of your other
            ' code catches the exception. Because there is none of 
            ' your code on the call stack in this thread, there is nothing
            ' higher up the stack to catch the exception if you do not 
            ' handle it here. You can either log the exception or 
            ' invoke a delegate (as in the non-error case in this 
            ' example) to display the error on the form. In no case
            ' can you simply display the error without executing a delegate
            ' as in the Try block here. 

            ' You can create the delegate instance as you 
            ' invoke it, like this:
            Me.Invoke(New DisplayStatusDelegate(AddressOf DisplayStatus), _
             "Error: " & ex.Message)
        Finally
            isExecuting = False
        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. 

        ' If you do not include the Asynchronous Processing=true name/value pair,
        ' you wo not be able to execute the command asynchronously.

        Return "Data Source=(local);Integrated Security=true;" & _
        "Initial Catalog=AdventureWorks; Asynchronous Processing=true"
    End Function

    Private Sub Button1_Click(ByVal sender As System.Object, _
        ByVal e As System.EventArgs) Handles Button1.Click
        If isExecuting Then
            MessageBox.Show(Me, _
                "Already executing. Please wait until the current query " & _
                "has completed.")
        Else
            Dim command As SqlCommand
            Try
                DisplayStatus("Connecting...")
                connection = New SqlConnection(GetConnectionString())
                ' To emulate a long-running query, wait for 
                ' a few seconds before retrieving the real data.
                command = New SqlCommand( _
                 "WAITFOR DELAY '0:0:5';" & _
                 "SELECT ProductID, Name, ListPrice, Weight FROM Production.Product", _
                 connection)
                connection.Open()

                DisplayStatus("Executing...")
                isExecuting = True
                ' Although it is not required that you pass the 
                ' SqlCommand object as the second parameter in the 
                ' BeginExecuteReader call, doing so makes it easier
                ' to call EndExecuteReader in the callback procedure.
                Dim callback As New AsyncCallback(AddressOf HandleCallback)
                command.BeginExecuteReader(callback, command)

            Catch ex As Exception
                DisplayStatus("Error: " & ex.Message)
                If connection IsNot Nothing Then
                    connection.Close()
                End If
            End Try
        End If
    End Sub

    Private Sub Form1_FormClosing(ByVal sender As Object, _
        ByVal e As System.Windows.Forms.FormClosingEventArgs) _
        Handles Me.FormClosing
        If isExecuting Then
            MessageBox.Show(Me, "Cannot close the form until " & _
              "the pending asynchronous command has completed. Please wait...")
            e.Cancel = True
        End If
    End Sub
End Class

Commenti

Il BeginExecuteReader metodo avvia il processo di esecuzione asincrona di un'istruzione Transact-SQL o stored procedure che restituisce righe, in modo che le altre attività possano essere eseguite simultaneamente durante l'esecuzione dell'istruzione.The BeginExecuteReader method starts the process of asynchronously executing a Transact-SQL statement or stored procedure that returns rows, so that other tasks can run concurrently while the statement is executing. Al termine dell'istruzione, gli sviluppatori devono chiamare il EndExecuteReader metodo per terminare l'operazione e recuperare l'oggetto SqlDataReader restituito dal comando.When the statement has completed, developers must call the EndExecuteReader method to finish the operation and retrieve the SqlDataReader returned by the command. Il BeginExecuteReader metodo restituisce immediatamente un risultato, ma fino a quando il codice EndExecuteReader non esegue la chiamata al metodo corrispondente, non deve eseguire altre chiamate che avviano un'esecuzione sincrona o asincrona sullo stesso SqlCommand oggetto.The BeginExecuteReader method returns immediately, but until the code executes the corresponding EndExecuteReader method call, it must not execute any other calls that start a synchronous or asynchronous execution against the same SqlCommand object. La chiamata di EndExecuteReader prima del completamento dell'esecuzione del comando comporta il SqlCommand blocco dell'oggetto fino al termine dell'esecuzione.Calling the EndExecuteReader before the command's execution is completed cause the SqlCommand object to block until the execution is finished.

Il callback parametro consente di specificare un AsyncCallback delegato che viene chiamato al termine dell'istruzione.The callback parameter lets you specify an AsyncCallback delegate that is called when the statement has completed. È possibile chiamare il EndExecuteReader metodo da questa procedura del delegato o da qualsiasi altra posizione all'interno dell'applicazione.You can call the EndExecuteReader method from within this delegate procedure, or from any other location within your application. Inoltre, è possibile passare qualsiasi oggetto nel stateObject parametro e la procedura di callback può recuperare queste informazioni usando la AsyncState Proprietà.In addition, you can pass any object in the stateObject parameter, and your callback procedure can retrieve this information using the AsyncState property.

Si noti che il testo del comando e i parametri vengono inviati al server in modo sincrono.Note that the command text and parameters are sent to the server synchronously. Se vengono inviati un comando di grandi dimensioni o molti parametri, questo metodo potrebbe bloccarsi durante le Scritture.If a large command or many parameters are sent, this method may block during writes. Una volta inviato il comando, il metodo viene restituito immediatamente senza attendere una risposta dal server, ovvero le letture sono asincrone.After the command is sent, the method returns immediately without waiting for an answer from the server--that is, reads are asynchronous. Anche se l'esecuzione del comando è asincrona, il recupero del valore è ancora sincrono.Although command execution is asynchronous, value fetching is still synchronous. Ciò significa che le chiamate a Read possono bloccarsi se sono necessari più dati e l'operazione di lettura della rete sottostante si blocca.This means that calls to Read may block if more data is required and the underlying network's read operation blocks.

Poiché la procedura di callback viene eseguita dall'interno di un thread in background fornito dal runtime di Microsoft .NET, è molto importante adottare un approccio rigoroso alla gestione delle interazioni tra thread all'interno delle applicazioni.Because the callback procedure executes from within a background thread supplied by the Microsoft .NET runtime, it is very important that you take a rigorous approach to handling cross-thread interactions from within your applications. Ad esempio, non è necessario interagire con il contenuto di un modulo dall'interno della procedura di callback. Se è necessario aggiornare il modulo, è necessario tornare al thread del modulo per poter eseguire il lavoro.For example, you must not interact with a form's contents from within your callback procedure; should you have to update the form, you must switch back to the form's thread in order to do your work. Nell'esempio riportato in questo argomento viene illustrato questo comportamento.The example in this topic demonstrates this behavior.

Tutti gli errori che si verificano durante l'esecuzione dell'operazione vengono generati come eccezioni nella procedura di callback.All errors that occur during the execution of the operation are thrown as exceptions in the callback procedure. È necessario gestire l'eccezione nella procedura di callback, non nell'applicazione principale.You must handle the exception in the callback procedure, not in the main application. Vedere l'esempio in questo argomento per ulteriori informazioni sulla gestione delle eccezioni nella procedura di callback.See the example in this topic for additional information on handling exceptions in the callback procedure.

Se si usa ExecuteReader o BeginExecuteReader per accedere ai dati xml, SQL Server restituisce tutti i risultati XML di lunghezza superiore a 2.033 caratteri in più righe di 2.033 caratteri.If you use ExecuteReader or BeginExecuteReader to access XML data, SQL Server returns any XML results greater than 2,033 characters in length in multiple rows of 2,033 characters each. Per evitare questo comportamento, utilizzare ExecuteXmlReader o BeginExecuteXmlReader per leggere query for XML.To avoid this behavior, use ExecuteXmlReader or BeginExecuteXmlReader to read FOR XML queries.

Questo metodo ignora la CommandTimeout Proprietà.This method ignores the CommandTimeout property.

Vedi anche

Si applica a

Prodotto Presentazione

BeginExecuteReader(AsyncCallback, Object, CommandBehavior)

Avvia l'esecuzione asincrona dell'istruzione o della stored procedure Transact-SQL descritta da SqlCommand, usando uno dei valori di CommandBehavior e recuperando uno o più set di risultati dal server, in base a una routine di callback e alle informazioni sullo stato.Initiates the asynchronous execution of the Transact-SQL statement or stored procedure that is described by this SqlCommand, using one of the CommandBehavior values, and retrieving one or more result sets from the server, given a callback procedure and state information.

public:
 IAsyncResult ^ BeginExecuteReader(AsyncCallback ^ callback, System::Object ^ stateObject, System::Data::CommandBehavior behavior);
public IAsyncResult BeginExecuteReader (AsyncCallback callback, object stateObject, System.Data.CommandBehavior behavior);
member this.BeginExecuteReader : AsyncCallback * obj * System.Data.CommandBehavior -> IAsyncResult
Public Function BeginExecuteReader (callback As AsyncCallback, stateObject As Object, behavior As CommandBehavior) As IAsyncResult

Parametri

callback
AsyncCallback

Delegato AsyncCallback richiamato al termine dell'esecuzione del comando.An AsyncCallback delegate that is invoked when the command's execution has completed. Passare null (Nothing in Microsoft Visual Basic) per indicare che non è necessario alcun callback.Pass null (Nothing in Microsoft Visual Basic) to indicate that no callback is required.

stateObject
Object

Oggetto di stato definito dall'utente e passato alla routine di callback.A user-defined state object that is passed to the callback procedure. Recuperare questo oggetto dalla routine di callback usando la proprietà AsyncState.Retrieve this object from within the callback procedure using the AsyncState property.

behavior
CommandBehavior

Uno dei valori di CommandBehavior che indica le opzioni per l'esecuzione dell'istruzione e il recupero dei dati.One of the CommandBehavior values, indicating options for statement execution and data retrieval.

Restituisce

IAsyncResult

Oggetto IAsyncResult che può essere usato per eseguire il polling o restare in attesa dei risultati, o entrambe le operazioni. Questo valore è necessario anche quando si richiama EndExecuteReader(IAsyncResult), che restituisce un'istanza di SqlDataReader che può essere usata per recuperare le righe restituite.An IAsyncResult that can be used to poll or wait for results, or both; this value is also needed when invoking EndExecuteReader(IAsyncResult), which returns a SqlDataReader instance which can be used to retrieve the returned rows.

Eccezioni

È stato usato un valore SqlDbType diverso da Binary o VarBinary quando Value era impostato su Stream.A SqlDbType other than Binary or VarBinary was used when Value was set to Stream. Per altre informazioni sul flusso, vedere Supporto del flusso SqlClient.For more information about streaming, see SqlClient Streaming Support.

-oppure--or-

È stato usato un valore SqlDbType diverso da Char, NChar, NVarChar, VarChar o Xml quando Value era impostato su TextReader.A SqlDbType other than Char, NChar, NVarChar, VarChar, or Xml was used when Value was set to TextReader.

-oppure--or-

È stato usato un valore SqlDbType diverso da Xml quando Value era impostato su XmlReader.A SqlDbType other than Xml was used when Value was set to XmlReader.

Qualsiasi errore che si è verificato durante l'esecuzione del testo del comando.Any error that occurred while executing the command text.

-oppure--or-

Si è verificato un timeout durante un'operazione di flusso.A timeout occurred during a streaming operation. Per altre informazioni sul flusso, vedere Supporto del flusso SqlClient.For more information about streaming, see SqlClient Streaming Support.

La coppia nome/valore "Asynchronous Processing=true" non è stata inclusa nella stringa di connessione che definisce la connessione per SqlCommand.The name/value pair "Asynchronous Processing=true" was not included within the connection string defining the connection for this SqlCommand.

-oppure--or-

L'elemento SqlConnection chiuso o eliminato durante l'operazione di flusso.The SqlConnection closed or dropped during a streaming operation. Per altre informazioni sul flusso, vedere Supporto del flusso SqlClient.For more information about streaming, see SqlClient Streaming Support.

Errore nell'oggetto Stream, XmlReader o TextReader durante un'operazione di flusso.An error occurred in a Stream, XmlReader or TextReader object during a streaming operation. Per altre informazioni sul flusso, vedere Supporto del flusso SqlClient.For more information about streaming, see SqlClient Streaming Support.

L'oggetto Stream, XmlReader o TextReader è stato chiuso durante l'operazione di flusso.The Stream, XmlReader or TextReader object was closed during a streaming operation. Per altre informazioni sul flusso, vedere Supporto del flusso SqlClient.For more information about streaming, see SqlClient Streaming Support.

Esempio

Nell'applicazione Windows seguente viene illustrato l'uso del metodo BeginExecuteReader, eseguendo un'istruzione Transact-SQL che include un ritardo di pochi secondi (emulando un comando con esecuzione prolungata).The following Windows application demonstrates the use of the BeginExecuteReader method, executing a Transact-SQL statement that includes a delay of a few seconds (emulating a long-running command). Poiché l'esempio esegue il comando in modo asincrono, il form rimane reattivo mentre è in attesa dei risultati.Because the sample executes the command asynchronously, the form remains responsive while awaiting the results. Questo esempio passa l'oggetto in esecuzione SqlCommand come stateObject parametro; in questo modo è semplice recuperare l' SqlCommand oggetto dall'interno della routine di callback, in modo che il codice possa chiamare il EndExecuteReader metodo corrispondente alla chiamata iniziale a BeginExecuteReader .This example passes the executing SqlCommand object as the stateObject parameter; doing so makes it simple to retrieve the SqlCommand object from within the callback procedure, so that the code can call the EndExecuteReader method corresponding to the initial call to BeginExecuteReader.

In questo esempio vengono illustrate molte tecniche importanti.This example demonstrates many important techniques. Ciò include la chiamata a un metodo che interagisce con il form da un thread separato.This includes calling a method that interacts with the form from a separate thread. In questo esempio viene inoltre illustrato come impedire agli utenti di eseguire un comando più volte simultaneamente e come è necessario assicurarsi che il form non venga chiuso prima che venga chiamata la procedura di callback.In addition, this example demonstrates how you must block users from executing a command multiple times concurrently, and how you must make sure that the form does not close before the callback procedure is called.

Per impostare questo esempio, creare una nuova applicazione Windows.To set up this example, create a new Windows application. Inserire un controllo Button , un DataGridView controllo e un Label controllo sul form (accettando il nome predefinito per ogni controllo).Put a Button control, a DataGridView control, and a Label control on the form (accepting the default name for each control). Aggiungere il codice seguente alla classe del form, modificando la stringa di connessione in base alle esigenze dell'ambiente.Add the following code to the form's class, modifying the connection string as needed for your environment.

Questo esempio passa il CommandBehavior.CloseConnection valore nel behavior parametro, facendo in modo che l'oggetto restituito SqlDataReader chiuda automaticamente la connessione quando viene chiusa.This example passes the CommandBehavior.CloseConnection value in the behavior parameter, causing the returned SqlDataReader to automatically close its connection when it is closed.

using System.Data.SqlClient;

namespace Microsoft.AdoDotNet.CodeSamples
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        // Hook up the form's Load event handler (you can double-click on
        // the form's design surface in Visual Studio), and then add
        // this code to the form's class:
        // You need this delegate in order to fill the grid from
        // a thread other than the form's thread. See the HandleCallback
        // procedure for more information.
        private delegate void FillGridDelegate(SqlDataReader reader);

        // You need this delegate to update the status bar.
        private delegate void DisplayStatusDelegate(string Text);

        // This flag ensures that the user does not attempt
        // to restart the command or close the form while the
        // asynchronous command is executing.
        private bool isExecuting;

        private void DisplayStatus(string Text)
        {
            this.label1.Text = Text;
        }

        private void FillGrid(SqlDataReader reader)
        {
            try
            {
                DataTable table = new DataTable();
                table.Load(reader);
                this.dataGridView1.DataSource = table;
                DisplayStatus("Ready");
            }
            catch (Exception ex)
            {
                // Because you are guaranteed this procedure
                // is running from within the form's thread,
                // it can directly interact with members of the form.
                DisplayStatus(string.Format("Ready (last attempt failed: {0})",
                    ex.Message));
            }
            finally
            {
                // Closing the reader also closes the connection,
                // because this reader was created using the
                // CommandBehavior.CloseConnection value.
                if (reader != null)
                {
                    reader.Close();
                }
            }
        }

        private void HandleCallback(IAsyncResult result)
        {
            try
            {
                // Retrieve the original command object, passed
                // to this procedure in the AsyncState property
                // of the IAsyncResult parameter.
                SqlCommand command = (SqlCommand)result.AsyncState;
                SqlDataReader reader = command.EndExecuteReader(result);
                // You may not interact with the form and its contents
                // from a different thread, and this callback procedure
                // is all but guaranteed to be running from a different thread
                // than the form. Therefore you cannot simply call code that
                // fills the grid, like this:
                // FillGrid(reader);
                // Instead, you must call the procedure from the form's thread.
                // One simple way to accomplish this is to call the Invoke
                // method of the form, which calls the delegate you supply
                // from the form's thread.
                FillGridDelegate del = new FillGridDelegate(FillGrid);
                this.Invoke(del, reader);
                // Do not close the reader here, because it is being used in
                // a separate thread. Instead, have the procedure you have
                // called close the reader once it is done with it.
            }
            catch (Exception ex)
            {
                // Because you are now running code in a separate thread,
                // if you do not handle the exception here, none of your other
                // code catches the exception. Because there is none of
                // your code on the call stack in this thread, there is nothing
                // higher up the stack to catch the exception if you do not
                // handle it here. You can either log the exception or
                // invoke a delegate (as in the non-error case in this
                // example) to display the error on the form. In no case
                // can you simply display the error without executing a delegate
                // as in the try block here.
                // You can create the delegate instance as you
                // invoke it, like this:
                this.Invoke(new DisplayStatusDelegate(DisplayStatus), "Error: " +
                    ex.Message);
            }
            finally
            {
                isExecuting = false;
            }
        }

        private string GetConnectionString()
        {
            // To avoid storing the connection string in your code,
            // you can retrieve it from a configuration file.

            // If you do not include the Asynchronous Processing=true name/value pair,
            // you wo not be able to execute the command asynchronously.
            return "Data Source=(local);Integrated Security=true;" +
                "Initial Catalog=AdventureWorks; Asynchronous Processing=true";
        }

        private void button1_Click(object sender, System.EventArgs e)
        {
            if (isExecuting)
            {
                MessageBox.Show(this,
                    "Already executing. Please wait until the current query " +
                    "has completed.");
            }
            else
            {
                SqlCommand command = null;
                SqlConnection connection = null;
                try
                {
                    DisplayStatus("Connecting...");
                    connection = new SqlConnection(GetConnectionString());
                    // To emulate a long-running query, wait for
                    // a few seconds before retrieving the real data.
                    command = new SqlCommand("WAITFOR DELAY '0:0:5';" +
                        "SELECT ProductID, Name, ListPrice, Weight FROM Production.Product",
                        connection);
                    connection.Open();

                    DisplayStatus("Executing...");
                    isExecuting = true;
                    // Although it is not required that you pass the
                    // SqlCommand object as the second parameter in the
                    // BeginExecuteReader call, doing so makes it easier
                    // to call EndExecuteReader in the callback procedure.
                    AsyncCallback callback = new AsyncCallback(HandleCallback);
                    command.BeginExecuteReader(callback, command,
                        CommandBehavior.CloseConnection);
                }
                catch (Exception ex)
                {
                    DisplayStatus("Error: " + ex.Message);
                    if (connection != null)
                    {
                        connection.Close();
                    }
                }
            }
        }

        private void Form1_Load(object sender, System.EventArgs e)
        {
            this.button1.Click += new System.EventHandler(this.button1_Click);
            this.FormClosing += new FormClosingEventHandler(Form1_FormClosing);
        }

        void Form1_FormClosing(object sender, FormClosingEventArgs e)
        {
            if (isExecuting)
            {
                MessageBox.Show(this, "Cannot close the form until " +
                    "the pending asynchronous command has completed. Please wait...");
                e.Cancel = true;
            }
        }
    }
}
Imports System.Data.SqlClient

Public Class Form1
    ' Add this code to the form's class:
    ' You this delegate in order to fill the grid from
    ' a thread other than the form's thread. See the HandleCallback
    ' procedure for more information.
    Private Delegate Sub FillGridDelegate(ByVal reader As SqlDataReader)

    ' You need this delegate to update the status bar.
    Private Delegate Sub DisplayStatusDelegate(ByVal Text As String)

    ' This flag ensures that the user does not attempt
    ' to restart the command or close the form while the 
    ' asynchronous command is executing.
    Private isExecuting As Boolean

    Private Sub DisplayStatus(ByVal Text As String)
        Me.Label1.Text = Text
    End Sub

    Private Sub FillGrid(ByVal reader As SqlDataReader)
        Try
            Dim table As New DataTable
            table.Load(reader)
            Me.DataGridView1.DataSource = table
            DisplayStatus("Ready")

        Catch ex As Exception
            ' Because you are guaranteed this procedure
            ' is running from within the form's thread,
            ' it can directly interact with members of the form.
            DisplayStatus(String.Format("Ready (last attempt failed: {0})", ex.Message))
        Finally
            ' Closing the reader also closes the connection,
            ' because this reader was created using the 
            ' CommandBehavior.CloseConnection value.
            If reader IsNot Nothing Then
                reader.Close()
            End If
        End Try
    End Sub

    Private Sub HandleCallback(ByVal result As IAsyncResult)
        Try
            ' Retrieve the original command object, passed
            ' to this procedure in the AsyncState property
            ' of the IAsyncResult parameter.
            Dim command As SqlCommand = CType(result.AsyncState, SqlCommand)
            Dim reader As SqlDataReader = command.EndExecuteReader(result)

            ' You may not interact with the form and its contents
            ' from a different thread, and this callback procedure
            ' is all but guaranteed to be running from a different thread
            ' than the form. Therefore you cannot simply call code that 
            ' fills the grid, like this:
            ' FillGrid(reader)

            ' Instead, you must call the procedure from the form's thread.
            ' One simple way to accomplish this is to call the Invoke
            ' method of the form, which calls the delegate you supply
            ' from the form's thread. 
            Dim del As New FillGridDelegate(AddressOf FillGrid)
            Me.Invoke(del, reader)

            ' Do not close the reader here, because it is being used in 
            ' a separate thread. Instead, have the procedure you have
            ' called close the reader once it is done with it.

        Catch ex As Exception
            ' Because you are now running code in a separate thread, 
            ' if you do not handle the exception here, none of your other
            ' code catches the exception. Because there is none of 
            ' your code on the call stack in this thread, there is nothing
            ' higher up the stack to catch the exception if you do not 
            ' handle it here. You can either log the exception or 
            ' invoke a delegate (as in the non-error case in this 
            ' example) to display the error on the form. In no case
            ' can you simply display the error without executing a delegate
            ' as in the Try block here. 

            ' You can create the delegate instance as you 
            ' invoke it, like this:
            Me.Invoke(New DisplayStatusDelegate(AddressOf DisplayStatus), _
             "Error: " & ex.Message)
        Finally
            isExecuting = False
        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. 

        ' If you do not include the Asynchronous Processing=true name/value pair,
        ' you wo not be able to execute the command asynchronously.

        Return "Data Source=(local);Integrated Security=true;" & _
        "Initial Catalog=AdventureWorks; Asynchronous Processing=true"
    End Function

    Private Sub Button1_Click(ByVal sender As System.Object, _
        ByVal e As System.EventArgs) Handles Button1.Click
        If isExecuting Then
            MessageBox.Show(Me, "Already executing. Please wait until the current query " & _
             "has completed.")
        Else
            Dim connection As SqlConnection
            Dim command As SqlCommand
            Try
                DisplayStatus("Connecting...")
                connection = New SqlConnection(GetConnectionString())
                ' To emulate a long-running query, wait for 
                ' a few seconds before retrieving the real data.
                command = New SqlCommand( _
                 "WAITFOR DELAY '0:0:5';" & _
                 "SELECT ProductID, Name, ListPrice, Weight FROM Production.Product", _
                 connection)
                connection.Open()

                DisplayStatus("Executing...")
                isExecuting = True
                ' Although it is not required that you pass the 
                ' SqlCommand object as the second parameter in the 
                ' BeginExecuteReader call, doing so makes it easier
                ' to call EndExecuteReader in the callback procedure.
                Dim callback As New AsyncCallback(AddressOf HandleCallback)
                command.BeginExecuteReader(callback, command, _
                  CommandBehavior.CloseConnection)

            Catch ex As Exception
                DisplayStatus("Error: " & ex.Message)
                If connection IsNot Nothing Then
                    connection.Close()
                End If
            End Try
        End If
    End Sub

    Private Sub Form1_FormClosing(ByVal sender As Object, _
        ByVal e As System.Windows.Forms.FormClosingEventArgs) Handles Me.FormClosing
        If isExecuting Then
            MessageBox.Show(Me, "Cannot close the form until " & _
             "the pending asynchronous command has completed. Please wait...")
            e.Cancel = True
        End If
    End Sub
End Class

Commenti

Il BeginExecuteReader metodo avvia il processo di esecuzione asincrona di un'istruzione Transact-SQL o stored procedure che restituisce righe, in modo che le altre attività possano essere eseguite simultaneamente durante l'esecuzione dell'istruzione.The BeginExecuteReader method starts the process of asynchronously executing a Transact-SQL statement or stored procedure that returns rows, so that other tasks can run concurrently while the statement is executing. Al termine dell'istruzione, gli sviluppatori devono chiamare il EndExecuteReader metodo per terminare l'operazione e recuperare l'oggetto SqlDataReader restituito dal comando.When the statement has completed, developers must call the EndExecuteReader method to finish the operation and retrieve the SqlDataReader returned by the command. Il BeginExecuteReader metodo restituisce immediatamente un risultato, ma fino a quando il codice EndExecuteReader non esegue la chiamata al metodo corrispondente, non deve eseguire altre chiamate che avviano un'esecuzione sincrona o asincrona sullo stesso SqlCommand oggetto.The BeginExecuteReader method returns immediately, but until the code executes the corresponding EndExecuteReader method call, it must not execute any other calls that start a synchronous or asynchronous execution against the same SqlCommand object. La chiamata di EndExecuteReader prima del completamento dell'esecuzione del comando comporta il SqlCommand blocco dell'oggetto fino al termine dell'esecuzione.Calling the EndExecuteReader before the command's execution is completed causes the SqlCommand object to block until the execution is finished.

Il callback parametro consente di specificare un AsyncCallback delegato che viene chiamato al termine dell'istruzione.The callback parameter lets you specify an AsyncCallback delegate that is called when the statement has completed. È possibile chiamare il EndExecuteReader metodo da questa procedura del delegato o da qualsiasi altra posizione all'interno dell'applicazione.You can call the EndExecuteReader method from within this delegate procedure, or from any other location within your application. Inoltre, è possibile passare qualsiasi oggetto nel stateObject parametro e la procedura di callback può recuperare queste informazioni usando la AsyncState Proprietà.In addition, you can pass any object in the stateObject parameter, and your callback procedure can retrieve this information using the AsyncState property.

Il behavior parametro consente di specificare le opzioni che controllano il comportamento del comando e la relativa connessione.The behavior parameter lets you specify options that control the behavior of the command and its connection. Questi valori possono essere combinati insieme (usando l'operatore del linguaggio di programmazione Or ); in genere, gli sviluppatori usano il CloseConnection valore per assicurarsi che la connessione venga chiusa dal runtime quando SqlDataReader viene chiuso.These values can be combined together (using the programming language's Or operator); generally, developers use the CloseConnection value to make sure that the connection is closed by the runtime when the SqlDataReader is closed. Gli sviluppatori possono anche ottimizzare il comportamento di SqlDataReader specificando il SingleRow valore quando è noto in anticipo che l'istruzione Transact-SQL o stored procedure restituisce solo una singola riga.Developers can also optimize the behavior of the SqlDataReader by specifying the SingleRow value when it is known in advance that the Transact-SQL statement or stored procedure only returns a single row.

Si noti che il testo del comando e i parametri vengono inviati al server in modo sincrono.Note that the command text and parameters are sent to the server synchronously. Se vengono inviati un comando di grandi dimensioni o molti parametri, questo metodo potrebbe bloccarsi durante le Scritture.If a large command or many parameters are sent, this method may block during writes. Una volta inviato il comando, il metodo viene restituito immediatamente senza attendere una risposta dal server, ovvero le letture sono asincrone.After the command is sent, the method returns immediately without waiting for an answer from the server--that is, reads are asynchronous. Anche se l'esecuzione del comando è asincrona, il recupero del valore è ancora sincrono.Although command execution is asynchronous, value fetching is still synchronous. Ciò significa che le chiamate a Read possono bloccarsi se sono necessari più dati e l'operazione di lettura della rete sottostante si blocca.This means that calls to Read may block if more data is required and the underlying network's read operation blocks.

Poiché la procedura di callback viene eseguita dall'interno di un thread in background fornito dal Microsoft .NET Common Language Runtime, è molto importante adottare un approccio rigoroso alla gestione delle interazioni tra thread all'interno delle applicazioni.Because the callback procedure executes from within a background thread supplied by the Microsoft .NET common language runtime, it is very important that you take a rigorous approach to handling cross-thread interactions from within your applications. Ad esempio, non è necessario interagire con il contenuto di un modulo dalla procedura di callback. se è necessario aggiornare il modulo, è necessario tornare al thread del modulo per poter eseguire il lavoro.For example, you must not interact with a form's contents from within your callback procedure--should you have to update the form, you must switch back to the form's thread in order to do your work. Nell'esempio riportato in questo argomento viene illustrato questo comportamento.The example in this topic demonstrates this behavior.

Tutti gli errori che si verificano durante l'esecuzione dell'operazione vengono generati come eccezioni nella procedura di callback.All errors that occur during the execution of the operation are thrown as exceptions in the callback procedure. È necessario gestire l'eccezione nella procedura di callback, non nell'applicazione principale.You must handle the exception in the callback procedure, not in the main application. Vedere l'esempio in questo argomento per ulteriori informazioni sulla gestione delle eccezioni nella procedura di callback.See the example in this topic for additional information on handling exceptions in the callback procedure.

Se si usa ExecuteReader o BeginExecuteReader per accedere ai dati xml, SQL Server restituirà tutti i risultati XML di lunghezza superiore a 2.033 caratteri in più righe di 2.033 caratteri.If you use ExecuteReader or BeginExecuteReader to access XML data, SQL Server will return any XML results greater than 2,033 characters in length in multiple rows of 2,033 characters each. Per evitare questo comportamento, utilizzare ExecuteXmlReader o BeginExecuteXmlReader per leggere query for XML.To avoid this behavior, use ExecuteXmlReader or BeginExecuteXmlReader to read FOR XML queries.

Questo metodo ignora la CommandTimeout Proprietà.This method ignores the CommandTimeout property.

Vedi anche

Si applica a

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