ZUgreifen auf FILESTREAM-Daten mit OpenSqlFilestream

Gilt für:SQL Server

Die OpenSqlFilestream-API ruft ein Win32-kompatibles Dateihandle für ein im Dateisystem gespeichertes FILESTREAM-Blob (Binary Large Object) ab. Das Handle kann an eine der folgenden Windows32-APIs übergeben werden: ReadFile, WriteFile, TransmitFile, SetFilePointer, SetEndOfFileoder FlushFileBuffers. Wenn Sie dieses Handle an eine andere Win32-API übergeben, wird der Fehler ERROR_ACCESS_DENIED zurückgegeben. Sie müssen das Handle schließen, indem Sie es an die Win32- CloseHandle -API übergeben, bevor für die Transaktion ein Commit oder ein Rollback ausgeführt wird. Wenn das Handle nicht geschlossen wird, treten serverseitige Ressourcenverluste auf.

Sie müssen den Zugriff auf alle FILESTREAM-Datencontainer in einer SQL Server-Transaktion ausführen. Transact-SQL-Anweisungen können auch in derselben Transaktion ausgeführt werden. Damit wird die Konsistenz zwischen SQL-Daten und FILESTREAM-BLOB gewahrt.

Um mit Win32 auf FILESTREAM BLOB-Daten zuzugreifen, muss die Windows-Autorisierung aktiviert sein.

Syntax

  
HANDLE OpenSqlFilestream (  
    LPCWSTR FilestreamPath,  
    SQL_FILESTREAM_DESIRED_ACCESS DesiredAccess,  
    ULONG OpenOptions,  
    LPBYTE FilestreamTransactionContext,  
    SIZE_T FilestreamTransactionContextLength,  
    PLARGE_INTEGER AllocationSize);  

Parameter

FilestreamPath
[in] Ist der nvarchar(max) -Pfad, der von der Funktion PathName zurückgegeben wird. PathName muss aus dem Kontext eines Kontos aufgerufen werden, das ÜBER SQL Server SELECT- oder UPDATE-Berechtigungen für die FILESTREAM-Tabelle und -Spalte verfügt.

DesiredAccess
[in] Legt den verwenden Modus so fest, dass ein Zugriff auf FILESTREAM-BLOB-Daten erfolgt. Dieser Wert wird an die Funktion DeviceIoControlübergeben.

OpenOptions
[in] Die Dateiattribute und Flags. Dieser Parameter kann auch jede Kombination der folgenden Flags umfassen.

FilestreamTransactionContext
[in] Der Wert, der von der Funktion GET_FILESTREAM_TRANSACTION_CONTEXT zurückgegeben wird.

FilestreamTransactionContextLength
[in] Anzahl von Bytes in den varbinary(max) -Daten, die von der Funktion GET_FILESTREAM_TRANSACTION_CONTEXT zurückgegeben werden. Die Funktion gibt ein Array von n Bytes zurück. n wird von der Funktion bestimmt und ist eine Eigenschaft des Bytearrays, das zurückgegeben wird.

AllocationSize
[in] Bestimmt die anfängliche Zuweisungsgröße der Datendatei in Bytes. Wird im Lesemodus ignoriert. Dieser Parameter kann NULL sein; in diesem Fall wird das Standarddateisystemverhalten verwendet.

Rückgabewert

Wenn die Funktion erfolgreich ausgeführt wurde, ist der Rückgabewert ein offenes Handle zu einer angegebenen Datei. Wenn die Funktion fehlschlägt, ist der Rückgabewert INVALID_HANDLE_VALUE. Rufen Sie für erweiterte Fehlerinformationen GetLastError() auf.

Beispiele

Die folgenden Beispiele zeigen, wie Sie die OpenSqlFilestream -API verwenden, um ein Win32-Handle abzurufen.

using System.IO;
using System;
using System.Collections.Generic;
using System.Text;
using System.Data;
using System.Data.SqlClient;
using System.Data.SqlTypes;

namespace FILESTREAM
{
    class Program
    {
        static void Main(string[] args)
        {
            SqlConnection sqlConnection = new SqlConnection(
                "Integrated Security=true;server=(local)");

            SqlCommand sqlCommand = new SqlCommand();
            sqlCommand.Connection = sqlConnection;

            try
            {
                sqlConnection.Open();

                //The first task is to retrieve the file path
                //of the SQL FILESTREAM BLOB that we want to
                //access in the application.

                sqlCommand.CommandText =
                      "SELECT Chart.PathName()"
                    + " FROM Archive.dbo.Records"
                    + " WHERE SerialNumber = 3";

                String filePath = null;

                Object pathObj = sqlCommand.ExecuteScalar();
                if (DBNull.Value != pathObj)
                    filePath = (string)pathObj;
                else
                {
                    throw new System.Exception(
                        "Chart.PathName() failed"
                      + " to read the path name "
                      + " for the Chart column.");
                }

                //The next task is to obtain a transaction
                //context. All FILESTREAM BLOB operations
                //occur within a transaction context to
                //maintain data consistency.

                //All SQL FILESTREAM BLOB access must occur in 
                //a transaction. MARS-enabled connections
                //have specific rules for batch scoped transactions,
                //which the Transact-SQL BEGIN TRANSACTION statement
                //violates. To avoid this issue, client applications 
                //should use appropriate API facilities for transaction management, 
                //management, such as the SqlTransaction class.

                SqlTransaction transaction = sqlConnection.BeginTransaction("mainTranaction");
                sqlCommand.Transaction = transaction;

                sqlCommand.CommandText =
                    "SELECT GET_FILESTREAM_TRANSACTION_CONTEXT()";

                Object obj = sqlCommand.ExecuteScalar();
                byte[] txContext = (byte[])obj;

                //The next step is to obtain a handle that
                //can be passed to the Win32 FILE APIs.

                SqlFileStream sqlFileStream = new SqlFileStream(filePath, txContext, FileAccess.ReadWrite);

                byte[] buffer = new byte[512];

                int numBytes = 0;

                //Write the string, "EKG data." to the FILESTREAM BLOB.
                //In your application this string would be replaced with
                //the binary data that you want to write.

                string someData = "EKG data.";
                Encoding unicode = Encoding.GetEncoding(0);

                sqlFileStream.Write(unicode.GetBytes(someData.ToCharArray()),
                    0,
                    Encoding.GetBytes());

                //Read the data from the FILESTREAM
                //BLOB.

                sqlFileStream.Seek(0L, SeekOrigin.Begin);

                numBytes = sqlFileStream.Read(buffer, 0, buffer.Length);

                string readData = unicode.GetString(buffer);

                if (numBytes != 0)
                    Console.WriteLine(readData);

                //Because reading and writing are finished, FILESTREAM 
                //must be closed. This closes the c# FileStream class, 
                //but does not necessarily close the underlying 
                //FILESTREAM handle. 
                sqlFileStream.Close();

                //The final step is to commit or roll back the read and write
                //operations that were performed on the FILESTREAM BLOB.

                sqlCommand.Transaction.Commit();
            }
            catch (System.Exception ex)
            {
                Console.WriteLine(ex.ToString());
            }
            finally
            {
                sqlConnection.Close();
            }
            return;
        }
    }
}

Imports System.IO
Imports System 
Imports System.Collections.Generic 
Imports System.Text 
Imports System.Data 
Imports System.Data.SqlClient 
Imports System.Data.SqlTypes 

Module Module1
    Public Sub Main(ByVal args As String())
        '        Dim sqlConnection As New SqlConnection("Integrated Security=true;server=(local)")
        Dim sqlConnection As New SqlConnection("Integrated Security=true;server=kellyreyue\MSSQL1")

        Dim sqlCommand As New SqlCommand()
        sqlCommand.Connection = sqlConnection

        Try
            sqlConnection.Open()

            'The first task is to retrieve the file path 
            'of the SQL FILESTREAM BLOB that we want to 
            'access in the application. 

            sqlCommand.CommandText = "SELECT Chart.PathName()" + " FROM Archive.dbo.Records" + " WHERE SerialNumber = 3"

            Dim filePath As String = Nothing

            Dim pathObj As Object = sqlCommand.ExecuteScalar()
            If Not pathObj.Equals(DBNull.Value) Then
                filePath = DirectCast(pathObj, String)
            Else
                Throw New System.Exception("Chart.PathName() failed" + " to read the path name " + " for the Chart column.")
            End If

            'The next task is to obtain a transaction 
            'context. All FILESTREAM BLOB operations 
            'occur within a transaction context to 
            'maintain data consistency. 

            'All SQL FILESTREAM BLOB access must occur in 
            'a transaction. MARS-enabled connections 
            'have specific rules for batch scoped transactions, 
            'which the Transact-SQL BEGIN TRANSACTION statement 
            'violates. To avoid this issue, client applications 
            'should use appropriate API facilities for transaction management, 
            'management, such as the SqlTransaction class. 

            Dim transaction As SqlTransaction = sqlConnection.BeginTransaction("mainTranaction")
            sqlCommand.Transaction = transaction

            sqlCommand.CommandText = "SELECT GET_FILESTREAM_TRANSACTION_CONTEXT()"

            Dim obj As Object = sqlCommand.ExecuteScalar()
            Dim txContext As Byte() = Nothing

            Dim contextLength As UInteger

            If Not obj.Equals(DBNull.Value) Then
                txContext = DirectCast(obj, Byte())
                contextLength = txContext.Length()
            Else
                Dim message As String = "GET_FILESTREAM_TRANSACTION_CONTEXT() failed"
                Throw New System.Exception(message)
            End If

            'The next step is to obtain a handle that 
            'can be passed to the Win32 FILE APIs. 

            Dim sqlFileStream As New SqlFileStream(filePath, txContext, FileAccess.ReadWrite)

            Dim buffer As Byte() = New Byte(511) {}

            Dim numBytes As Integer = 0

            'Write the string, "EKG data." to the FILESTREAM BLOB. 
            'In your application this string would be replaced with 
            'the binary data that you want to write. 

            Dim someData As String = "EKG data."
            Dim unicode As Encoding = Encoding.GetEncoding(0)

            sqlFileStream.Write(unicode.GetBytes(someData.ToCharArray()), 0, Encoding.GetBytes())

            'Read the data from the FILESTREAM 
            'BLOB. 

            sqlFileStream.Seek(0, SeekOrigin.Begin)

            numBytes = sqlFileStream.Read(buffer, 0, buffer.Length)

            Dim readData As String = unicode.GetString(buffer)

            If numBytes <> 0 Then
                Console.WriteLine(readData)
            End If

            'Because reading and writing are finished, FILESTREAM 
            'must be closed. This closes the c# FileStream class, 
            'but does not necessarily close the underlying 
            'FILESTREAM handle. 
            sqlFileStream.Close()

            'The final step is to commit or roll back the read and write 
            'operations that were performed on the FILESTREAM BLOB. 

            sqlCommand.Transaction.Commit()
        Catch ex As System.Exception
            Console.WriteLine(ex.ToString())
        Finally
            sqlConnection.Close()
        End Try
        Return
    End Sub
End Module

#include <windows.h>
#include <sql.h>
#include<sqltypes.h>
#include<sqlext.h>
#include <stdio.h>
#include <msodbcsql.h>

#define COPYBUFFERSIZE 4096

/// <summary>
///This class iterates though the ODBC error queue and prints all of the
///accumulated error messages to the console.
/// </summary>

class ODBCErrors
{
private:
    int         m_iLine;    //Source code line on which the error occurred
    SQLSMALLINT m_type;     //Type of handle on which the error occurred
    SQLHANDLE   m_handle;   //ODBC handle on which the error occurred

public:
    /// <summary>
    ///Default constructor for the ODBCErrors class
    ///</summary>

    ODBCErrors()
    {
        m_iLine  = -1;
        m_type   = 0;
        m_handle = SQL_NULL_HANDLE;
    }

    /// <summary>
    ///Constructor for the ODBCErrors class
    /// </summary>
    /// <param name="iLine">
    /// This parameter is the source code line
    /// at which the error occurred.
    ///</param>
    /// <param name="type">
    /// This parameter is the type of ODBC handle passed in
    /// the next parameter.
    ///</param>
    /// <param name="handle">
    /// This parameter is the handle on which the error occurred.
    ///</param>

    ODBCErrors(int iLine, SQLSMALLINT type, SQLHANDLE handle)
    {
        m_iLine  = iLine;
        m_type   = type;
        m_handle = handle;
    }

    ///<summary>
    /// This method iterates though the error stack for the handle passed
    /// into the constructor and displays those errors on the console.
    ///</summary>

    void Print()
    {
        SQLSMALLINT i = 0, len = 0;
        SQLINTEGER  native;
        SQLTCHAR    state[9], text[256];
        SQLRETURN   sqlReturn = SQL_SUCCESS;

        if ( m_handle == SQL_NULL_HANDLE )
        {
            wprintf_s(TEXT("The error handle is not a valid handle.\n"), m_iLine);
            return;
        }

        wprintf_s(TEXT("Error Line(%d)\n"), m_iLine);

        while( sqlReturn == SQL_SUCCESS )
        {
            len = 0;

            sqlReturn = SQLGetDiagRec(
                m_type,
                m_handle,
                ++i,
                state,
                &native,
                text,
                sizeof(text)/sizeof(SQLTCHAR),
                &len);

            if ( SQL_SUCCEEDED(sqlReturn) )
                wprintf_s(TEXT("Error(%d, %ld, %s) : %s\n"), i, native, state, text);
        }
    }
};


BOOL CopyFileToSQL(LPTSTR srcFilePath, LPTSTR dstFilePath, LPBYTE transactionToken, SQLINTEGER cbTransactionToken)
{
    BOOL bRetCode = FALSE;

    HANDLE srcHandle = INVALID_HANDLE_VALUE;
    HANDLE dstHandle = INVALID_HANDLE_VALUE;
    BYTE   buffer[COPYBUFFERSIZE] = { 0 };

    TCHAR *szErrMsgSrc   = TEXT("Error opening source file.");
    TCHAR *szErrMsgDst   = TEXT("Error opening destFile file.");
    TCHAR *szErrMsgRead  = TEXT("Error reading source file.");
    TCHAR *szErrMsgWrite = TEXT("Error writing SQL file.");

    try
    {
        if ( (srcHandle = CreateFile(
            srcFilePath,
            GENERIC_READ,
            FILE_SHARE_READ,
            NULL,
            OPEN_EXISTING,
            FILE_FLAG_SEQUENTIAL_SCAN,
            NULL)) == INVALID_HANDLE_VALUE )
            throw szErrMsgSrc;

        if ( (dstHandle =  OpenSqlFilestream(
            dstFilePath,
            Write,
            0,
            transactionToken,
            cbTransactionToken,
            0)) == INVALID_HANDLE_VALUE)
            throw szErrMsgDst;

        DWORD bytesRead = 0;
        DWORD bytesWritten = 0;

        do
        {
            if ( ReadFile(srcHandle, buffer, COPYBUFFERSIZE, &bytesRead, NULL) == 0 )
                throw szErrMsgRead;

            if (bytesRead > 0)
            {
                if ( WriteFile(dstHandle, buffer, bytesRead, &bytesWritten, NULL) == 0 )
                    throw szErrMsgWrite;
            }
        } while (bytesRead > 0);

        bRetCode = TRUE;
    }
    catch( TCHAR *szErrMsg )
    {
        wprintf_s(szErrMsg);
        bRetCode = FALSE;
    }

    if ( srcHandle != INVALID_HANDLE_VALUE )
        CloseHandle(srcHandle);

    if ( dstHandle != INVALID_HANDLE_VALUE )
        CloseHandle(dstHandle);

    return bRetCode;
}

void main()
{
    TCHAR *sqlDBQuery =
       TEXT("INSERT INTO Archive.dbo.Records(Id, SerialNumber, Chart)")
       TEXT(" OUTPUT GET_FILESTREAM_TRANSACTION_CONTEXT(), inserted.Chart.PathName()")
       TEXT("VALUES (newid (), 5, CONVERT(VARBINARY, '**Temp**'))");

    SQLCHAR transactionToken[32];
    
    SQLHANDLE henv = SQL_NULL_HANDLE;
    SQLHANDLE hdbc              = SQL_NULL_HANDLE;
    SQLHANDLE hstmt             = SQL_NULL_HANDLE;

    try
    {
        //These statements Initialize ODBC for the client application and
        //connect to the database.

        if ( SQLAllocHandle(SQL_HANDLE_ENV, SQL_NULL_HANDLE, &henv) != SQL_SUCCESS )
            throw new ODBCErrors(__LINE__, SQL_HANDLE_ENV, henv);

        if ( SQLSetEnvAttr(henv, SQL_ATTR_ODBC_VERSION,(void*)SQL_OV_ODBC3, NULL) != SQL_SUCCESS )
            throw new ODBCErrors(__LINE__, SQL_HANDLE_ENV, henv);

        if ( SQLAllocHandle(SQL_HANDLE_DBC, henv, &hdbc) != SQL_SUCCESS )
            throw new ODBCErrors(__LINE__, SQL_HANDLE_ENV, henv);

        //This code assumes that the dataset name "Sql Server FILESTREAM"
        //has been previously created on the client computer system. An
        //ODBC DSN is created with the ODBC Data Source item in
        //the Windows Control Panel.

        if ( SQLConnect(hdbc, TEXT("Sql Server FILESTREAM"),
                SQL_NTS, NULL, 0, NULL, 0) <= 0 )
            throw new ODBCErrors(__LINE__, SQL_HANDLE_DBC, hdbc);

        //FILESTREAM requires that all read and write operations occur
        //within a transaction.
        if ( SQLSetConnectAttr(hdbc,
            SQL_ATTR_AUTOCOMMIT,
            (SQLPOINTER)SQL_AUTOCOMMIT_OFF,
            SQL_IS_UINTEGER) != SQL_SUCCESS )
            throw new ODBCErrors(__LINE__, SQL_HANDLE_DBC, hdbc);

        if ( SQLAllocHandle(SQL_HANDLE_STMT, hdbc, &hstmt) != SQL_SUCCESS )
            throw new ODBCErrors(__LINE__, SQL_HANDLE_DBC, hdbc);

        if ( SQLExecDirect(hstmt, sqlDBQuery, SQL_NTS) != SQL_SUCCESS )
            throw new ODBCErrors(__LINE__, SQL_HANDLE_STMT, hstmt);

        //Retrieve the transaction token.
        if ( SQLFetch(hstmt) != SQL_SUCCESS )
            throw new ODBCErrors(__LINE__, SQL_HANDLE_STMT, hstmt);

        SQLINTEGER cbTransactionToken = sizeof(transactionToken);

        if ( SQLGetData(hstmt, 1,
            SQL_C_BINARY,
            transactionToken,
            sizeof(transactionToken),
            &cbTransactionToken) != SQL_SUCCESS )
            throw new ODBCErrors(__LINE__, SQL_HANDLE_STMT, hstmt);

        //Retrieve the file path for the inserted record.

        TCHAR dstFilePath[1024];
        SQLINTEGER cbDstFilePath;

        if ( SQLGetData(hstmt, 2, SQL_C_TCHAR, dstFilePath, sizeof(dstFilePath), &cbDstFilePath) != SQL_SUCCESS )
            throw new ODBCErrors(__LINE__, SQL_HANDLE_STMT, hstmt);

        if ( SQLCloseCursor(hstmt) != SQL_SUCCESS )
            throw new ODBCErrors(__LINE__, SQL_HANDLE_STMT, hstmt);

        SQLUSMALLINT mode = SQL_ROLLBACK;

        if ( CopyFileToSQL(
            TEXT("C:\\Users\\Data\\chart1.jpg"),
            dstFilePath,
            transactionToken,
            cbTransactionToken) == TRUE )
            mode = SQL_COMMIT;

        SQLTransact(henv, hdbc, mode);
    }
    catch(ODBCErrors *pErrors)
    {
        pErrors->Print();
        delete pErrors;
    }

    if ( hstmt != SQL_NULL_HANDLE )
        SQLFreeHandle(SQL_HANDLE_STMT, hstmt);

    if ( hdbc != SQL_NULL_HANDLE )
        SQLDisconnect(hdbc);

    if ( hdbc != SQL_NULL_HANDLE )
        SQLFreeHandle(SQL_HANDLE_DBC, hdbc); 

    if ( henv != SQL_NULL_HANDLE )
        SQLFreeHandle(SQL_HANDLE_ENV, henv);
}

Hinweise

Dieses Beispiel wurde ursprünglich für den SQL Server Native Client (sqlncli.h) geschrieben, wurde jedoch aktualisiert, um den Microsoft OLE DB-Treiber (msoledbsql.h) für SQL Server zu verwenden. Der SQL Server Native Client (häufig abgekürzt mit SNAC) wurde aus SQL Server 2022 (16.x) und SQL Server Management Studio 19 (SSMS) entfernt. Sowohl der OLE DB-Anbieter für den SQL Server Native Client (SQLNCLI oder SQLNCLI11) als auch der Microsoft OLE DB-Legacyanbieter für SQL Server (SQLOLEDB) werden für Neuentwicklungen nicht empfohlen. Verwenden Sie in Zukunft den neuen Microsoft OLE DB-Treiber für SQL Server (MSOLEDBSQL).

Weitere Informationen

Binary Large Object (BLOB)-Daten (SQL Server)
Vornehmen von Teilupdates an FILESTREAM-Daten
Vermeiden von Konflikten mit Datenbankvorgängen in FILESTREAM-Anwendungen