SqlCommand.BeginExecuteReader SqlCommand.BeginExecuteReader SqlCommand.BeginExecuteReader SqlCommand.BeginExecuteReader Method

Definición

Inicia la ejecución asincrónica de la instrucción de Transact-SQL o del procedimiento almacenado que describe SqlCommand y recupera uno o varios conjuntos de resultados del servidor.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.

Sobrecargas

BeginExecuteReader() BeginExecuteReader() BeginExecuteReader() BeginExecuteReader()

Inicia la ejecución asincrónica de la instrucción de Transact-SQL o del procedimiento almacenado que describe SqlCommand y recupera uno o varios conjuntos de resultados del servidor.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) BeginExecuteReader(CommandBehavior) BeginExecuteReader(CommandBehavior) BeginExecuteReader(CommandBehavior)

Inicia la ejecución asincrónica de la instrucción de Transact-SQL o del procedimiento almacenado que describe SqlCommand utilizando uno de los valores de 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) BeginExecuteReader(AsyncCallback, Object) BeginExecuteReader(AsyncCallback, Object) BeginExecuteReader(AsyncCallback, Object)

Inicia la ejecución asincrónica de la instrucción de Transact-SQL o del procedimiento almacenado que describe SqlCommand y recupera uno o varios conjuntos de resultados del servidor, dados un procedimiento de devolución de llamada e información de estado.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) BeginExecuteReader(AsyncCallback, Object, CommandBehavior) BeginExecuteReader(AsyncCallback, Object, CommandBehavior) BeginExecuteReader(AsyncCallback, Object, CommandBehavior)

Inicia la ejecución asincrónica de la instrucción de Transact-SQL o del procedimiento almacenado que describe SqlCommand, utilizando uno de los valores de CommandBehavior y recuperando uno o varios conjuntos de resultados del servidor, a partir del procedimiento de devolución de llamada e información de estado dados.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() BeginExecuteReader() BeginExecuteReader() BeginExecuteReader()

Inicia la ejecución asincrónica de la instrucción de Transact-SQL o del procedimiento almacenado que describe SqlCommand y recupera uno o varios conjuntos de resultados del servidor.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

Devoluciones

IAsyncResult que se puede utilizar para sondear y/o esperar los resultados; este valor también es necesario al invocar a EndExecuteReader(IAsyncResult), que devuelve una instancia de SqlDataReader que se puede usar para recuperar las filas devueltas.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.

Excepciones

Un valor SqlDbType distinto a Binary o VarBinary se usó cuando Value se estableció en Stream.A SqlDbType other than Binary or VarBinary was used when Value was set to Stream. Para obtener más información sobre el streaming, vea Compatibilidad de transmisión de datos de SqlClient.For more information about streaming, see SqlClient Streaming Support.

O bien-or-

Un valor SqlDbType distinto a Char, NChar, NVarChar, VarChar o Xml se usó cuando Value se estableció en TextReader.A SqlDbType other than Char, NChar, NVarChar, VarChar, or Xml was used when Value was set to TextReader.

O bien-or-

Se usó un SqlDbType distinto de Xml cuando Value se estableció en XmlReader.A SqlDbType other than Xml was used when Value was set to XmlReader.

Cualquier error que se produjo al ejecutar el texto del comando.Any error that occurred while executing the command text.

O bien-or-

Se agotó el tiempo de espera durante una operación de streaming.A timeout occurred during a streaming operation. Para más información sobre el streaming, vea Compatibilidad con el streaming de SqlClient.For more information about streaming, see SqlClient Streaming Support.

El par nombre/valor "Asynchronous Processing=true" no se incluyó dentro de la cadena de conexión que define la conexión para este SqlCommand.The name/value pair "Asynchronous Processing=true" was not included within the connection string defining the connection for this SqlCommand.

o bien-or-

La SqlConnection se cerró o se interrumpió durante una operación de streaming.The SqlConnection closed or dropped during a streaming operation. Para obtener más información sobre el streaming, vea Compatibilidad de transmisión de datos de SqlClient.For more information about streaming, see SqlClient Streaming Support.

Se produjo un error en un objeto Stream, XmlReader o TextReader durante una operación de streaming.An error occurred in a Stream, XmlReader or TextReader object during a streaming operation. Para obtener más información sobre el streaming, vea Compatibilidad de transmisión de datos de SqlClient.For more information about streaming, see SqlClient Streaming Support.

El objeto Stream, XmlReader o TextReader se cerró durante una operación de streaming.The Stream, XmlReader or TextReader object was closed during a streaming operation. Para obtener más información sobre el streaming, vea Compatibilidad de transmisión de datos de SqlClient.For more information about streaming, see SqlClient Streaming Support.

Ejemplos

La siguiente aplicación de consola inicia el proceso de recuperación de un lector de datos de forma asincrónica.The following console application starts the process of retrieving a data reader asynchronously. Mientras espera los resultados, esta aplicación simple se ubica en un bucle, investigando IsCompleted el valor de la propiedad.While waiting for the results, this simple application sits in a loop, investigating the IsCompleted property value. En cuanto se complete el proceso, el código recupera SqlDataReader y muestra su contenido.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

Comentarios

El BeginExecuteReader método inicia el proceso de ejecución asincrónica de una instrucción de Transact-SQL o un procedimiento almacenado que devuelve filas, de modo que se puedan ejecutar otras tareas simultáneamente mientras se ejecuta la instrucción.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. Cuando la instrucción se haya completado, los desarrolladores deben EndExecuteReader llamar al método para finalizar la operación y SqlDataReader recuperar el devuelto por el comando.When the statement has completed, developers must call the EndExecuteReader method to finish the operation and retrieve the SqlDataReader returned by the command. El BeginExecuteReader método se devuelve inmediatamente, pero hasta que el código ejecuta la EndExecuteReader llamada al método correspondiente, no debe ejecutar ninguna otra llamada que inicie una ejecución sincrónica o asincrónica en el mismo SqlCommand objeto.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. Llamar a SqlCommand antes de que se complete la ejecución del comando hace que el objeto se bloquee hasta que finalice la ejecución. EndExecuteReaderCalling the EndExecuteReader before the command's execution is completed causes the SqlCommand object to block until the execution is finished.

Tenga en cuenta que el texto y los parámetros del comando se envían al servidor de forma sincrónica.Note that the command text and parameters are sent to the server synchronously. Si se envían comandos grandes o muchos parámetros, este método puede bloquearse durante las operaciones de escritura.If a large command or many parameters are sent, this method may block during writes. Después de enviar el comando, el método vuelve inmediatamente sin esperar una respuesta del servidor; es decir, las lecturas son asincrónicas.After the command is sent, the method returns immediately without waiting for an answer from the server--that is, reads are asynchronous. Aunque la ejecución del comando es asincrónica, la obtención de valores sigue siendo sincrónica.Although command execution is asynchronous, value fetching is still synchronous. Esto significa que las llamadas Read a pueden bloquearse si se requieren más datos y se bloquea la operación de lectura de la red subyacente.This means that calls to Read may block if more data is required and the underlying network's read operation blocks.

Dado que esta sobrecarga no admite un procedimiento de devolución de llamada, los desarrolladores deben sondear para determinar si el comando se IsCompleted ha completado, IAsyncResult utilizando la propiedad BeginExecuteReader del devuelto por el método o esperar a que finalice uno o más comandos que usan AsyncWaitHandle la propiedad del devuelto. IAsyncResultBecause 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.

Si usa ExecuteReader o BeginExecuteReader para tener acceso a los datos XML, SQL Server devolverá los resultados XML de más de 2.033 caracteres de longitud en varias filas de 2.033 caracteres cada uno.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. Para evitar este comportamiento, use ExecuteXmlReader o BeginExecuteXmlReader para leer las consultas for XML.To avoid this behavior, use ExecuteXmlReader or BeginExecuteXmlReader to read FOR XML queries.

Consulte también:

BeginExecuteReader(CommandBehavior) BeginExecuteReader(CommandBehavior) BeginExecuteReader(CommandBehavior) BeginExecuteReader(CommandBehavior)

Inicia la ejecución asincrónica de la instrucción de Transact-SQL o del procedimiento almacenado que describe SqlCommand utilizando uno de los valores de 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

Parámetros

behavior
CommandBehavior CommandBehavior CommandBehavior CommandBehavior

Uno de los valores de CommandBehavior, que indican las opciones para la ejecución de instrucciones y la recuperación de datos.One of the CommandBehavior values, indicating options for statement execution and data retrieval.

Devoluciones

IAsyncResult que se puede utilizar para sondear y/o esperar los resultados; este valor también es necesario al invocar a EndExecuteReader(IAsyncResult), que devuelve una instancia de SqlDataReader que se puede usar para recuperar las filas devueltas.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.

Excepciones

Un valor SqlDbType distinto a Binary o VarBinary se usó cuando Value se estableció en Stream.A SqlDbType other than Binary or VarBinary was used when Value was set to Stream. Para obtener más información sobre el streaming, vea Compatibilidad de transmisión de datos de SqlClient.For more information about streaming, see SqlClient Streaming Support.

O bien-or-

Un valor SqlDbType distinto a Char, NChar, NVarChar, VarChar o Xml se usó cuando Value se estableció en TextReader.A SqlDbType other than Char, NChar, NVarChar, VarChar, or Xml was used when Value was set to TextReader.

o bien-or-

Se usó un SqlDbType distinto de Xml cuando Value se estableció en XmlReader.A SqlDbType other than Xml was used when Value was set to XmlReader.

Cualquier error que se produjo al ejecutar el texto del comando.Any error that occurred while executing the command text.

o bien-or-

Se agotó el tiempo de espera durante una operación de streaming.A timeout occurred during a streaming operation. Para más información sobre el streaming, vea Compatibilidad con el streaming de SqlClient.For more information about streaming, see SqlClient Streaming Support.

El par nombre/valor "Asynchronous Processing=true" no se incluyó dentro de la cadena de conexión que define la conexión para este SqlCommand.The name/value pair "Asynchronous Processing=true" was not included within the connection string defining the connection for this SqlCommand.

O bien-or-

La SqlConnection se cerró o se interrumpió durante una operación de streaming.The SqlConnection closed or dropped during a streaming operation. Para obtener más información sobre el streaming, vea Compatibilidad de transmisión de datos de SqlClient.For more information about streaming, see SqlClient Streaming Support.

Se produjo un error en un objeto Stream, XmlReader o TextReader durante una operación de streaming.An error occurred in a Stream, XmlReader or TextReader object during a streaming operation. Para obtener más información sobre el streaming, vea Compatibilidad de transmisión de datos de SqlClient.For more information about streaming, see SqlClient Streaming Support.

El objeto Stream, XmlReader o TextReader se cerró durante una operación de streaming.The Stream, XmlReader or TextReader object was closed during a streaming operation. Para obtener más información sobre el streaming, vea Compatibilidad de transmisión de datos de SqlClient.For more information about streaming, see SqlClient Streaming Support.

Ejemplos

La siguiente aplicación de consola inicia el proceso de recuperación de un lector de datos de forma asincrónica.The following console application starts the process of retrieving a data reader asynchronously. Mientras espera los resultados, esta aplicación simple se ubica en un bucle, investigando IsCompleted el valor de la propiedad.While waiting for the results, this simple application sits in a loop, investigating the IsCompleted property value. Una vez completado el proceso, el código recupera SqlDataReader y muestra su contenido.Once the process has completed, the code retrieves the SqlDataReader and displays its contents.

En este ejemplo también se CommandBehavior.CloseConnection pasan CommandBehavior.SingleRow los valores y en el parámetro Behavior, lo que hace que la conexión se SqlDataReader cierre con la devuelta se cierre y para optimizar el resultado de una sola fila.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

Comentarios

El BeginExecuteReader método inicia el proceso de ejecución asincrónica de una instrucción de Transact-SQL o un procedimiento almacenado que devuelve filas, de modo que se puedan ejecutar otras tareas simultáneamente mientras se ejecuta la instrucción.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. Cuando la instrucción se haya completado, los desarrolladores deben EndExecuteReader llamar al método para finalizar la operación y SqlDataReader recuperar el devuelto por el comando.When the statement has completed, developers must call the EndExecuteReader method to finish the operation and retrieve the SqlDataReader returned by the command. El BeginExecuteReader método se devuelve inmediatamente, pero hasta que el código ejecuta la EndExecuteReader llamada al método correspondiente, no debe ejecutar ninguna otra llamada que inicie una ejecución sincrónica o asincrónica en el mismo SqlCommand objeto.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. Llamar a SqlCommand antes de que se complete la ejecución del comando hace que el objeto se bloquee hasta que finalice la ejecución. EndExecuteReaderCalling the EndExecuteReader before the command's execution is completed causes the SqlCommand object to block until the execution is finished.

El behavior parámetro permite especificar opciones que controlan el comportamiento del comando y su conexión.The behavior parameter lets you specify options that control the behavior of the command and its connection. Estos valores se pueden combinar juntos (mediante el operador del lenguaje OR de programación); por lo general, CommandBehavior.CloseConnection los desarrolladores usan el valor para asegurarse de que el tiempo de ejecución cierra SqlDataReader la conexión cuando se cierra.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.

Tenga en cuenta que el texto y los parámetros del comando se envían al servidor de forma sincrónica.Note that the command text and parameters are sent to the server synchronously. Si se envían comandos grandes o muchos parámetros, este método puede bloquearse durante las operaciones de escritura.If a large command or many parameters are sent, this method may block during writes. Después de enviar el comando, el método vuelve inmediatamente sin esperar una respuesta del servidor; es decir, las lecturas son asincrónicas.After the command is sent, the method returns immediately without waiting for an answer from the server--that is, reads are asynchronous. Aunque la ejecución del comando es asincrónica, la obtención de valores sigue siendo sincrónica.Although command execution is asynchronous, value fetching is still synchronous. Esto significa que las llamadas Read a pueden bloquearse si se requieren más datos y se bloquea la operación de lectura de la red subyacente.This means that calls to Read may block if more data is required and the underlying network's read operation blocks.

Dado que esta sobrecarga no admite un procedimiento de devolución de llamada, los desarrolladores deben sondear para determinar si el comando se IsCompleted ha completado, IAsyncResult utilizando la propiedad BeginExecuteNonQuery del devuelto por el método o esperar a que finalice uno o más comandos que usan AsyncWaitHandle la propiedad del devuelto. IAsyncResultBecause 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.

Si utiliza ExecuteReader o BeginExecuteReader para obtener acceso a los datos XML, SQL Server devuelve los resultados XML de más de 2.033 caracteres de longitud en varias filas de 2.033 caracteres cada uno.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. Para evitar este comportamiento, use ExecuteXmlReader o BeginExecuteXmlReader para leer las consultas for XML.To avoid this behavior, use ExecuteXmlReader or BeginExecuteXmlReader to read FOR XML queries.

Consulte también:

BeginExecuteReader(AsyncCallback, Object) BeginExecuteReader(AsyncCallback, Object) BeginExecuteReader(AsyncCallback, Object) BeginExecuteReader(AsyncCallback, Object)

Inicia la ejecución asincrónica de la instrucción de Transact-SQL o del procedimiento almacenado que describe SqlCommand y recupera uno o varios conjuntos de resultados del servidor, dados un procedimiento de devolución de llamada e información de estado.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

Parámetros

callback
AsyncCallback AsyncCallback AsyncCallback AsyncCallback

Delegado AsyncCallback que se invoca cuando finaliza la ejecución del comando.An AsyncCallback delegate that is invoked when the command's execution has completed. Pase null (Nothing en Microsoft Visual Basic) para indicar que no se requiere ninguna devolución de llamada.Pass null (Nothing in Microsoft Visual Basic) to indicate that no callback is required.

stateObject
Object Object Object Object

Objeto de estado definido por el usuario que se pasa al procedimiento de devolución de llamada.A user-defined state object that is passed to the callback procedure. Recupere este objeto desde el procedimiento de devolución de llamada mediante la propiedad AsyncState.Retrieve this object from within the callback procedure using the AsyncState property.

Devoluciones

IAsyncResult que se puede utilizar para sondear y/o esperar los resultados; este valor también es necesario al invocar a EndExecuteReader(IAsyncResult), que devuelve una instancia de SqlDataReader que se puede usar para recuperar las filas devueltas.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.

Excepciones

Un valor SqlDbType distinto a Binary o VarBinary se usó cuando Value se estableció en Stream.A SqlDbType other than Binary or VarBinary was used when Value was set to Stream. Para obtener más información sobre el streaming, vea Compatibilidad de transmisión de datos de SqlClient.For more information about streaming, see SqlClient Streaming Support.

O bien-or-

Un valor SqlDbType distinto a Char, NChar, NVarChar, VarChar o Xml se usó cuando Value se estableció en TextReader.A SqlDbType other than Char, NChar, NVarChar, VarChar, or Xml was used when Value was set to TextReader.

O bien-or-

Se usó un SqlDbType distinto de Xml cuando Value se estableció en XmlReader.A SqlDbType other than Xml was used when Value was set to XmlReader.

Cualquier error que se produjo al ejecutar el texto del comando.Any error that occurred while executing the command text.

O bien-or-

Se agotó el tiempo de espera durante una operación de streaming.A timeout occurred during a streaming operation. Para más información sobre el streaming, vea Compatibilidad con el streaming de SqlClient.For more information about streaming, see SqlClient Streaming Support.

El par nombre/valor "Asynchronous Processing=true" no se incluyó dentro de la cadena de conexión que define la conexión para este SqlCommand.The name/value pair "Asynchronous Processing=true" was not included within the connection string defining the connection for this SqlCommand.

O bien-or-

La SqlConnection se cerró o se interrumpió durante una operación de streaming.The SqlConnection closed or dropped during a streaming operation. Para obtener más información sobre el streaming, vea Compatibilidad de transmisión de datos de SqlClient.For more information about streaming, see SqlClient Streaming Support.

Se produjo un error en un objeto Stream, XmlReader o TextReader durante una operación de streaming.An error occurred in a Stream, XmlReader or TextReader object during a streaming operation. Para obtener más información sobre el streaming, vea Compatibilidad de transmisión de datos de SqlClient.For more information about streaming, see SqlClient Streaming Support.

El objeto Stream, XmlReader o TextReader se cerró durante una operación de streaming.The Stream, XmlReader or TextReader object was closed during a streaming operation. Para obtener más información sobre el streaming, vea Compatibilidad de transmisión de datos de SqlClient.For more information about streaming, see SqlClient Streaming Support.

Ejemplos

La siguiente aplicación Windows muestra el uso del método BeginExecuteReader, mediante la ejecución de una instrucción Transact-SQL que incluye un retraso de algunos segundos (al emular un comando cuya ejecución tiene una larga duración).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). Dado que el ejemplo ejecuta el comando de forma asincrónica, el formulario sigue respondiendo mientras se esperan los resultados.Because the sample executes the command asynchronously, the form remains responsive while awaiting the results. En este ejemplo se pasa el SqlCommand objeto de ejecución stateObject como parámetro; de esta forma, resulta sencillo recuperar SqlCommand el objeto desde el procedimiento de devolución de llamada, de modo que el EndExecuteReader código pueda llamar al método correspondiente a la llamada inicial 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.

En este ejemplo se muestran muchas técnicas importantes.This example demonstrates many important techniques. Esto incluye llamar a un método que interactúa con el formulario desde un subproceso independiente.This includes calling a method that interacts with the form from a separate thread. Además, en este ejemplo se muestra cómo debe impedir que los usuarios ejecuten un comando varias veces simultáneamente y cómo debe asegurarse de que el formulario no se cierra antes de que se llame al procedimiento de devolución de llamada.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.

Para realizar este ejemplo, cree una nueva aplicación Windows.To set up this example, create a new Windows application. Coloque un Button control, un DataGridView control y un Label control en el formulario (aceptando el nombre predeterminado de cada control).Put a Button control, a DataGridView control, and a Label control on the form (accepting the default name for each control). Agregue el código siguiente a la clase del formulario y modifique la cadena de conexión según sea necesario para su entorno.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

Comentarios

El BeginExecuteReader método inicia el proceso de ejecución asincrónica de una instrucción de Transact-SQL o un procedimiento almacenado que devuelve filas, de modo que se puedan ejecutar otras tareas simultáneamente mientras se ejecuta la instrucción.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. Cuando la instrucción se haya completado, los desarrolladores deben EndExecuteReader llamar al método para finalizar la operación y SqlDataReader recuperar el devuelto por el comando.When the statement has completed, developers must call the EndExecuteReader method to finish the operation and retrieve the SqlDataReader returned by the command. El BeginExecuteReader método se devuelve inmediatamente, pero hasta que el código ejecuta la EndExecuteReader llamada al método correspondiente, no debe ejecutar ninguna otra llamada que inicie una ejecución sincrónica o asincrónica en el mismo SqlCommand objeto.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. Llamar a SqlCommand antes de que se complete la ejecución del comando hace que el objeto se bloquee hasta que finalice la ejecución. EndExecuteReaderCalling the EndExecuteReader before the command's execution is completed cause the SqlCommand object to block until the execution is finished.

El callback parámetro permite especificar un AsyncCallback delegado al que se llama cuando se ha completado la instrucción.The callback parameter lets you specify an AsyncCallback delegate that is called when the statement has completed. Puede llamar al EndExecuteReader método desde este procedimiento delegado o desde cualquier otra ubicación dentro de la aplicación.You can call the EndExecuteReader method from within this delegate procedure, or from any other location within your application. Además, puede pasar cualquier objeto en el stateObject parámetro y el procedimiento de devolución de llamada puede recuperar esta información mediante la AsyncState propiedad.In addition, you can pass any object in the stateObject parameter, and your callback procedure can retrieve this information using the AsyncState property.

Tenga en cuenta que el texto y los parámetros del comando se envían al servidor de forma sincrónica.Note that the command text and parameters are sent to the server synchronously. Si se envían comandos grandes o muchos parámetros, este método puede bloquearse durante las operaciones de escritura.If a large command or many parameters are sent, this method may block during writes. Después de enviar el comando, el método vuelve inmediatamente sin esperar una respuesta del servidor; es decir, las lecturas son asincrónicas.After the command is sent, the method returns immediately without waiting for an answer from the server--that is, reads are asynchronous. Aunque la ejecución del comando es asincrónica, la obtención de valores sigue siendo sincrónica.Although command execution is asynchronous, value fetching is still synchronous. Esto significa que las llamadas Read a pueden bloquearse si se requieren más datos y se bloquea la operación de lectura de la red subyacente.This means that calls to Read may block if more data is required and the underlying network's read operation blocks.

Dado que el procedimiento de devolución de llamada se ejecuta desde dentro de un subproceso en segundo plano proporcionado por el motor en tiempo de ejecución de Microsoft .NET, es muy importante que adopte un enfoque riguroso para controlar las interacciones entre subprocesos desde dentro de sus aplicaciones.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. Por ejemplo, no debe interactuar con el contenido de un formulario desde el procedimiento de devolución de llamada. Si tiene que actualizar el formulario, debe volver al subproceso del formulario para realizar su trabajo.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. En el ejemplo de este tema se muestra este comportamiento.The example in this topic demonstrates this behavior.

Todos los errores que se producen durante la ejecución de la operación se producen como excepciones en el procedimiento de devolución de llamada.All errors that occur during the execution of the operation are thrown as exceptions in the callback procedure. Debe controlar la excepción en el procedimiento de devolución de llamada, no en la aplicación principal.You must handle the exception in the callback procedure, not in the main application. Vea el ejemplo de este tema para obtener información adicional sobre el control de excepciones en el procedimiento de devolución de llamada.See the example in this topic for additional information on handling exceptions in the callback procedure.

Si utiliza ExecuteReader o BeginExecuteReader para obtener acceso a los datos XML, SQL Server devuelve los resultados XML de más de 2.033 caracteres de longitud en varias filas de 2.033 caracteres cada uno.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. Para evitar este comportamiento, use ExecuteXmlReader o BeginExecuteXmlReader para leer las consultas for XML.To avoid this behavior, use ExecuteXmlReader or BeginExecuteXmlReader to read FOR XML queries.

Consulte también:

BeginExecuteReader(AsyncCallback, Object, CommandBehavior) BeginExecuteReader(AsyncCallback, Object, CommandBehavior) BeginExecuteReader(AsyncCallback, Object, CommandBehavior) BeginExecuteReader(AsyncCallback, Object, CommandBehavior)

Inicia la ejecución asincrónica de la instrucción de Transact-SQL o del procedimiento almacenado que describe SqlCommand, utilizando uno de los valores de CommandBehavior y recuperando uno o varios conjuntos de resultados del servidor, a partir del procedimiento de devolución de llamada e información de estado dados.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

Parámetros

callback
AsyncCallback AsyncCallback AsyncCallback AsyncCallback

Delegado AsyncCallback que se invoca cuando finaliza la ejecución del comando.An AsyncCallback delegate that is invoked when the command's execution has completed. Pase null (Nothing en Microsoft Visual Basic) para indicar que no se requiere ninguna devolución de llamada.Pass null (Nothing in Microsoft Visual Basic) to indicate that no callback is required.

stateObject
Object Object Object Object

Objeto de estado definido por el usuario que se pasa al procedimiento de devolución de llamada.A user-defined state object that is passed to the callback procedure. Recupere este objeto desde el procedimiento de devolución de llamada mediante la propiedad AsyncState.Retrieve this object from within the callback procedure using the AsyncState property.

behavior
CommandBehavior CommandBehavior CommandBehavior CommandBehavior

Uno de los valores de CommandBehavior, que indican las opciones para la ejecución de instrucciones y la recuperación de datos.One of the CommandBehavior values, indicating options for statement execution and data retrieval.

Devoluciones

IAsyncResult que se puede utilizar para sondear y/o esperar los resultados; este valor también es necesario al invocar a EndExecuteReader(IAsyncResult), que devuelve una instancia de SqlDataReader que se puede usar para recuperar las filas devueltas.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.

Excepciones

Un valor SqlDbType distinto a Binary o VarBinary se usó cuando Value se estableció en Stream.A SqlDbType other than Binary or VarBinary was used when Value was set to Stream. Para obtener más información sobre el streaming, vea Compatibilidad de transmisión de datos de SqlClient.For more information about streaming, see SqlClient Streaming Support.

O bien-or-

Un valor SqlDbType distinto a Char, NChar, NVarChar, VarChar o Xml se usó cuando Value se estableció en TextReader.A SqlDbType other than Char, NChar, NVarChar, VarChar, or Xml was used when Value was set to TextReader.

O bien-or-

Se usó un SqlDbType distinto de Xml cuando Value se estableció en XmlReader.A SqlDbType other than Xml was used when Value was set to XmlReader.

Cualquier error que se produjo al ejecutar el texto del comando.Any error that occurred while executing the command text.

O bien-or-

Se agotó el tiempo de espera durante una operación de streaming.A timeout occurred during a streaming operation. Para más información sobre el streaming, vea Compatibilidad con el streaming de SqlClient.For more information about streaming, see SqlClient Streaming Support.

El par nombre/valor "Asynchronous Processing=true" no se incluyó dentro de la cadena de conexión que define la conexión para este SqlCommand.The name/value pair "Asynchronous Processing=true" was not included within the connection string defining the connection for this SqlCommand.

O bien-or-

La SqlConnection se cerró o se interrumpió durante una operación de streaming.The SqlConnection closed or dropped during a streaming operation. Para obtener más información sobre el streaming, vea Compatibilidad de transmisión de datos de SqlClient.For more information about streaming, see SqlClient Streaming Support.

Se produjo un error en un objeto Stream, XmlReader o TextReader durante una operación de streaming.An error occurred in a Stream, XmlReader or TextReader object during a streaming operation. Para obtener más información sobre el streaming, vea Compatibilidad de transmisión de datos de SqlClient.For more information about streaming, see SqlClient Streaming Support.

El objeto Stream, XmlReader o TextReader se cerró durante una operación de streaming.The Stream, XmlReader or TextReader object was closed during a streaming operation. Para obtener más información sobre el streaming, vea Compatibilidad de transmisión de datos de SqlClient.For more information about streaming, see SqlClient Streaming Support.

Ejemplos

La siguiente aplicación Windows muestra el uso del método BeginExecuteReader, mediante la ejecución de una instrucción Transact-SQL que incluye un retraso de algunos segundos (al emular un comando cuya ejecución tiene una larga duración).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). Dado que el ejemplo ejecuta el comando de forma asincrónica, el formulario sigue respondiendo mientras se esperan los resultados.Because the sample executes the command asynchronously, the form remains responsive while awaiting the results. En este ejemplo se pasa el SqlCommand objeto de ejecución stateObject como parámetro; de esta forma, resulta sencillo recuperar SqlCommand el objeto desde el procedimiento de devolución de llamada, de modo que el EndExecuteReader código pueda llamar al método correspondiente a la llamada inicial 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.

En este ejemplo se muestran muchas técnicas importantes.This example demonstrates many important techniques. Esto incluye llamar a un método que interactúa con el formulario desde un subproceso independiente.This includes calling a method that interacts with the form from a separate thread. Además, en este ejemplo se muestra cómo debe impedir que los usuarios ejecuten un comando varias veces simultáneamente y cómo debe asegurarse de que el formulario no se cierra antes de que se llame al procedimiento de devolución de llamada.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.

Para realizar este ejemplo, cree una nueva aplicación Windows.To set up this example, create a new Windows application. Coloque un Button control, un DataGridView control y un Label control en el formulario (aceptando el nombre predeterminado de cada control).Put a Button control, a DataGridView control, and a Label control on the form (accepting the default name for each control). Agregue el código siguiente a la clase del formulario y modifique la cadena de conexión según sea necesario para su entorno.Add the following code to the form's class, modifying the connection string as needed for your environment.

Este ejemplo pasa el CommandBehavior.CloseConnection valor en el behavior parámetro, lo que hace SqlDataReader que el devuelto cierre automáticamente la conexión cuando está cerrada.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

Comentarios

El BeginExecuteReader método inicia el proceso de ejecución asincrónica de una instrucción de Transact-SQL o un procedimiento almacenado que devuelve filas, de modo que se puedan ejecutar otras tareas simultáneamente mientras se ejecuta la instrucción.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. Cuando la instrucción se haya completado, los desarrolladores deben EndExecuteReader llamar al método para finalizar la operación y SqlDataReader recuperar el devuelto por el comando.When the statement has completed, developers must call the EndExecuteReader method to finish the operation and retrieve the SqlDataReader returned by the command. El BeginExecuteReader método se devuelve inmediatamente, pero hasta que el código ejecuta la EndExecuteReader llamada al método correspondiente, no debe ejecutar ninguna otra llamada que inicie una ejecución sincrónica o asincrónica en el mismo SqlCommand objeto.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. Llamar a SqlCommand antes de que se complete la ejecución del comando hace que el objeto se bloquee hasta que finalice la ejecución. EndExecuteReaderCalling the EndExecuteReader before the command's execution is completed causes the SqlCommand object to block until the execution is finished.

El callback parámetro permite especificar un AsyncCallback delegado al que se llama cuando se ha completado la instrucción.The callback parameter lets you specify an AsyncCallback delegate that is called when the statement has completed. Puede llamar al EndExecuteReader método desde este procedimiento delegado o desde cualquier otra ubicación dentro de la aplicación.You can call the EndExecuteReader method from within this delegate procedure, or from any other location within your application. Además, puede pasar cualquier objeto en el stateObject parámetro y el procedimiento de devolución de llamada puede recuperar esta información mediante la AsyncState propiedad.In addition, you can pass any object in the stateObject parameter, and your callback procedure can retrieve this information using the AsyncState property.

El behavior parámetro permite especificar opciones que controlan el comportamiento del comando y su conexión.The behavior parameter lets you specify options that control the behavior of the command and its connection. Estos valores se pueden combinar juntos (mediante el operador del lenguaje Or de programación); por lo general, CloseConnection los desarrolladores usan el valor para asegurarse de que el tiempo de ejecución cierra SqlDataReader la conexión cuando se cierra.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. Los desarrolladores también pueden optimizar el comportamiento de SqlDataReader especificando el SingleRow valor cuando se sabe de antemano que la instrucción de Transact-SQL o el procedimiento almacenado solo devuelve una fila única.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.

Tenga en cuenta que el texto y los parámetros del comando se envían al servidor de forma sincrónica.Note that the command text and parameters are sent to the server synchronously. Si se envían comandos grandes o muchos parámetros, este método puede bloquearse durante las operaciones de escritura.If a large command or many parameters are sent, this method may block during writes. Después de enviar el comando, el método vuelve inmediatamente sin esperar una respuesta del servidor; es decir, las lecturas son asincrónicas.After the command is sent, the method returns immediately without waiting for an answer from the server--that is, reads are asynchronous. Aunque la ejecución del comando es asincrónica, la obtención de valores sigue siendo sincrónica.Although command execution is asynchronous, value fetching is still synchronous. Esto significa que las llamadas Read a pueden bloquearse si se requieren más datos y se bloquea la operación de lectura de la red subyacente.This means that calls to Read may block if more data is required and the underlying network's read operation blocks.

Dado que el procedimiento de devolución de llamada se ejecuta desde dentro de un subproceso en segundo plano proporcionado por el Common Language Runtime Microsoft .NET, es muy importante que adopte un enfoque riguroso para controlar las interacciones entre subprocesos desde dentro de sus aplicaciones.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. Por ejemplo, no debe interactuar con el contenido de un formulario desde el procedimiento de devolución de llamada; si tiene que actualizar el formulario, debe volver al subproceso del formulario para realizar su trabajo.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. En el ejemplo de este tema se muestra este comportamiento.The example in this topic demonstrates this behavior.

Todos los errores que se producen durante la ejecución de la operación se producen como excepciones en el procedimiento de devolución de llamada.All errors that occur during the execution of the operation are thrown as exceptions in the callback procedure. Debe controlar la excepción en el procedimiento de devolución de llamada, no en la aplicación principal.You must handle the exception in the callback procedure, not in the main application. Vea el ejemplo de este tema para obtener información adicional sobre el control de excepciones en el procedimiento de devolución de llamada.See the example in this topic for additional information on handling exceptions in the callback procedure.

Si usa ExecuteReader o BeginExecuteReader para tener acceso a los datos XML, SQL Server devolverá los resultados XML de más de 2.033 caracteres de longitud en varias filas de 2.033 caracteres cada uno.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. Para evitar este comportamiento, use ExecuteXmlReader o BeginExecuteXmlReader para leer las consultas for XML.To avoid this behavior, use ExecuteXmlReader or BeginExecuteXmlReader to read FOR XML queries.

Consulte también:

Se aplica a