GET_FILESTREAM_TRANSACTION_CONTEXT (Transact-SQL)

Restituisce un token che rappresenta il contesto di transazione corrente di una sessione. Il token viene utilizzato da un'applicazione per associare le operazioni di flusso di file system FILESTREAM alla transazione. Per un elenco di argomenti relativi a FILESTREAM, vedere Dati BLOB (Binary Large Object) (SQL Server).

Convenzioni della sintassi Transact-SQL

Sintassi

GET_FILESTREAM_TRANSACTION_CONTEXT ()

Tipo restituito

varbinary(max)

Valore restituito

Se la transazione non è stata avviata o se è stata annullata oppure se ne è stato eseguito il commit, viene restituito Null.

Osservazioni

La transazione deve essere esplicita. Utilizzare BEGIN TRANSACTION seguita da COMMIT TRANSACTION o ROLLBACK TRANSACTION.

Quando si chiama GET_FILESTREAM_TRANSACTION_CONTEXT, al chiamante viene concesso l'accesso al file system relativo alla transazione per la durata della transazione stessa. Per consentire a un altro utente di accedere alla transazione tramite il file system, utilizzare EXECUTE AS per eseguire GET_FILESTREAM_TRANSACTION_CONTEXT come un altro utente.

Esempi

Nell'esempio seguente viene utilizzato GET_FILESTREAM_TRANSACTION_CONTEXT in una transazione Transact-SQL per ottenerne il contesto.

using System;
using System.Data.SqlClient;
using System.Data;

namespace ConsoleApplication
{
    /// <summary>
    /// This class is a wrapper that contains methods for:
    /// 
    ///     GetTransactionContect() - Returns the current transaction context.
    ///     BeginTransaction() - Begins a transaction.
    ///     CommmitTransaction() - Commits the current transaction.
    /// 
    /// </summary>

    class SqlAccessWrapper
    {
        /// <summary>
        /// Returns a byte array that contains the current transaction
        /// context.
        /// </summary>
        /// <param name="sqlConnection">
        /// SqlConnection object that represents the instance of SQL Server
        /// from which to obtain the transaction context. 
        /// </param>
        /// <returns>
        /// If there is a current transaction context, the return
        /// value is an Object that represents the context.
        /// If there is not a current transaction context, the
        /// value returned is DBNull.Value.
        /// </returns>

        public Object GetTransactionContext(SqlConnection sqlConnection)
        {
            SqlCommand cmd = new SqlCommand();
            cmd.CommandText = "SELECT GET_FILESTREAM_TRANSACTION_CONTEXT()";
            cmd.CommandType = CommandType.Text;
            cmd.Connection = sqlConnection;

            return cmd.ExecuteScalar();

        }

        /// <summary>
        /// Begins the transaction.
        /// </summary>
        /// <param name="sqlConnection">
        /// SqlConnection object that represents the server
        /// on which to run the BEGIN TRANSACTION statement.
        /// </param>

        public void BeginTransaction(SqlConnection sqlConnection)
        {
            SqlCommand cmd = new SqlCommand();

            cmd.CommandText = "BEGIN TRANSACTION";
            cmd.CommandType = CommandType.Text;
            cmd.Connection = sqlConnection;

            cmd.ExecuteNonQuery();
        }

        /// <summary>
        /// Commits the transaction.
        /// </summary>
        /// <param name="sqlConnection">
        /// SqlConnection object that represents the instance of SQL Server
        /// on which to run the COMMIT statement.
        /// </param>

        public void CommitTransaction(SqlConnection sqlConnection)
        {
            SqlCommand cmd = new SqlCommand();

            cmd.CommandText = "COMMIT TRANSACTION";
            cmd.CommandType = CommandType.Text;
            cmd.Connection = sqlConnection;

            cmd.ExecuteNonQuery();
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            //Open a connection to the local instance of SQL Server.

            SqlConnection sqlConnection = new SqlConnection("Integrated Security=true;server=(local)");
            sqlConnection.Open();

            SqlAccessWrapper sql = new SqlAccessWrapper();

            //Create a transaction so that sql.GetTransactionContext() will succeed.
            sql.BeginTransaction(sqlConnection);

            //The transaction context will be stored in this array.
            Byte[] transactionToken;   

            Object txObj = sql.GetTransactionContext(sqlConnection);
            if (DBNull.Value != txObj)
            {
                transactionToken = (byte[])txObj;
                Console.WriteLine("Transaction context obtained.\n");
            }

            sql.CommitTransaction(sqlConnection);
        }
    }
}

Imports System
Imports System.Data.SqlClient
Imports System.Data

Namespace ConsoleApplication
    ''' <summary> 
    ''' This class is a wrapper that contains methods for: 
    ''' 
    ''' GetTransactionContect() - Returns the current transaction context. 
    ''' BeginTransaction() - Begins a transaction. 
    ''' CommmitTransaction() - Commits the current transaction. 
    ''' 
    ''' </summary> 

    Class SqlAccessWrapper
        ''' <summary> 
        ''' Returns a byte array that contains the current transaction 
        ''' context. 
        ''' </summary> 
        ''' <param name="sqlConnection"> 
        ''' SqlConnection object that represents the instance of SQL Server 
        ''' from which to obtain the transaction context. 
        ''' </param> 
        ''' <returns> 
        ''' If there is a current transaction context, the return 
        ''' value is an Object that represents the context. 
        ''' If there is not a current transaction context, the 
        ''' value returned is DBNull.Value. 
        ''' </returns> 

        Public Function GetTransactionContext(ByVal sqlConnection As SqlConnection) As Object
            Dim cmd As New SqlCommand()
            cmd.CommandText = "SELECT GET_FILESTREAM_TRANSACTION_CONTEXT()"
            cmd.CommandType = CommandType.Text
            cmd.Connection = sqlConnection

            Return cmd.ExecuteScalar()

        End Function

        ''' <summary> 
        ''' Begins the transaction. 
        ''' </summary> 
        ''' <param name="sqlConnection"> 
        ''' SqlConnection object that represents the server 
        ''' on which to run the BEGIN TRANSACTION statement. 
        ''' </param> 

        Public Sub BeginTransaction(ByVal sqlConnection As SqlConnection)
            Dim cmd As New SqlCommand()

            cmd.CommandText = "BEGIN TRANSACTION"
            cmd.CommandType = CommandType.Text
            cmd.Connection = sqlConnection

            cmd.ExecuteNonQuery()
        End Sub

        ''' <summary> 
        ''' Commits the transaction. 
        ''' </summary> 
        ''' <param name="sqlConnection"> 
        ''' SqlConnection object that represents the instance of SQL Server 
        ''' on which to run the COMMIT statement. 
        ''' </param> 

        Public Sub CommitTransaction(ByVal sqlConnection As SqlConnection)
            Dim cmd As New SqlCommand()

            cmd.CommandText = "COMMIT TRANSACTION"
            cmd.CommandType = CommandType.Text
            cmd.Connection = sqlConnection

            cmd.ExecuteNonQuery()
        End Sub
    End Class

    Class Program
        Shared Sub Main()
            '''Open a connection to the local instance of SQL Server.

            Dim sqlConnection As New SqlConnection("Integrated Security=true;server=(local)")
            sqlConnection.Open()

            Dim sql As New SqlAccessWrapper()

            '''Create a transaction so that sql.GetTransactionContext() will succeed. 
            sql.BeginTransaction(sqlConnection)

            '''The transaction context will be stored in this array. 
            Dim transactionToken As Byte()

            Dim txObj As Object = sql.GetTransactionContext(sqlConnection)

            '''If the returned object is not NULL, there is a valid transaction
            '''token, and it must be converted into a format that is usable within
            '''the application.

            If Not txObj.Equals(DBNull.Value) Then
                transactionToken = DirectCast(txObj, Byte())
                Console.WriteLine("Transaction context obtained." & Chr(10) & "")
            End If

            sql.CommitTransaction(sqlConnection)
        End Sub
    End Class
End Namespace

Vedere anche

Riferimento

PathName (Transact-SQL)

Concetti

Dati BLOB (Binary Large Object) (SQL Server)