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Realizar actualizaciones parciales de los datos FILESTREAM

  • Artículo

Se aplica a: SQL Server

Una aplicación utiliza FSCTL_SQL_FILESTREAM_FETCH_OLD_CONTENT para realizar actualizaciones parciales de los datos de FILESTREAM BLOB. La función DeviceIoControl pasa este valor y el controlador que OpenSqlFilestream devuelve al controlador FILESTREAM. A continuación, el controlador obliga a hacer una copia del lado servidor de los datos FILESTREAM actuales en el archivo al que el controlador hace referencia. Si la aplicación emite el valor FSCTL_SQL_FILESTREAM_FETCH_OLD_CONTENT una vez escrito el controlador, la última operación de escritura se conserva y se pierden las operaciones de escritura anteriores que se realizaron en el controlador.

Nota

FILESTREAM se basa en el protocolo SMB protocol para el acceso remoto.

Ejemplo

En el ejemplo siguiente se muestra cómo utilizar el valor FSCTL_SQL_FILESTREAM_FETCH_OLD_CONTENT para realizar una actualización parcial de un FILESTREAM BLOB insertado.

Nota

Este ejemplo requiere la tabla y la base de datos habilitadas para FILESTREAM que se crean en Crear una base de datos habilitada para FILESTREAM y Crear una tabla para almacenar datos FILESTREAM.

C++ 
#include <windows.h>
#include<sqlext.h>
#include <stdio.h>
#include <msodbcsql.h>
#include <tchar.h>
#include <strsafe.h>

/// <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);
        }
    }
};

/// <summary>
///This function waits for the overlapped IO operation to complete; TRUE
///is returned if the function completes successfully and FALSE is
///returned if an error occurs.
///</summary>

BOOL WaitForIOToComplete(HANDLE srcHandle, OVERLAPPED *pOverLapped, LPDWORD pBytes)
{
    DWORD bError = GetLastError();

    if ( bError == ERROR_HANDLE_EOF )
        return TRUE;

    //If GetLastError() does not return EOF or IO PENDING then
    //an error has occurred.
    if ( bError != ERROR_IO_PENDING )
        return FALSE;

    do
    {
        //In a real application you would perform non-blocking
        //processing here.
        SleepEx(0, TRUE);
        if ( GetOverlappedResult(srcHandle, pOverLapped, pBytes, FALSE) == 0 )
            return FALSE;
    } while( GetLastError() == ERROR_IO_PENDING );

    return TRUE;
}

/// <summary>
///This function performs a partial update of the inserted
///FILESTREAM BLOB.
///</summary>

BOOL UpdateBLOB(LPTSTR srcFilePath, LPBYTE transactionToken, SQLINTEGER cbTransactionToken)
{
    BOOL bRetCode        = FALSE;
    HANDLE srcHandle     = INVALID_HANDLE_VALUE;
    TCHAR *szErrMsgSrc   = TEXT("Error opening FILESTREAM BLOB.");
    TCHAR *szErrMsgRead  = TEXT("Error reading source file.");
    TCHAR *szErrMsgWrite = TEXT("Error writing SQL file.");
    TCHAR *szErrMsgIOCtl = TEXT("Error calling DeviceIoControl.");

    try
    {
        //Obtain a handle to the FILESTREAM BLOB data.
        srcHandle =  OpenSqlFilestream(srcFilePath,
                                       ReadWrite,
                                       0,
                                       transactionToken,
                                       cbTransactionToken,
                                       0);
        if ( srcHandle == INVALID_HANDLE_VALUE )
            throw szErrMsgSrc;

        //The DeviceIoControl API will fill in an return this
        //structure. This structure can be used to implement
        //overlapped IO.

        OVERLAPPED overlapped;
        ZeroMemory(&overlapped, sizeof (overlapped));

        DWORD bytesRead = 0;
        DWORD bytesWritten = 0;

        //If ReadFile is called it will return EOF because the
        //FILESTREAM BLOB data has not been copied to the open
        //File handle. Issuing This IOCTL will cause the server
        //to copy the BLOB data to the file referenced by the
        //srcHandle.

        if ( !DeviceIoControl(srcHandle,
                              FSCTL_SQL_FILESTREAM_FETCH_OLD_CONTENT,
                              NULL,
                              0,
                              NULL,
                              0,
                              NULL,
                              &overlapped))
        {
            throw szErrMsgIOCtl;
        }        

        //In a real application you would read more information than a
        //few bytes. This small sample is provided to illustrate how to
        //perform partial reads and writes starting at an offset within
        //the FILESTREAM BLOB.
        BYTE buffer[8];

        overlapped.Offset = 2;

        if ( ReadFile(srcHandle, buffer, 4, &bytesRead, &overlapped) == 0 )
            if ( WaitForIOToComplete(srcHandle, &overlapped, &bytesRead) == 0 )
                throw szErrMsgRead;

        //Change the word Temp currently stored in the BLOB to the 
        //word Done. Write the new word back to the FILESTREAM BLOB.
        buffer[0] = 'D';
        buffer[1] = 'o';
        buffer[2] = 'n';
        buffer[3] = 'e';

        if ( WriteFile(srcHandle, buffer, bytesRead, &bytesWritten, &overlapped) == 0 )
            if ( WaitForIOToComplete(srcHandle, &overlapped, &bytesWritten) == 0 )
                throw szErrMsgWrite;

        bRetCode = TRUE;
    }
    catch( TCHAR *szErrMsg )
    {
        LPTSTR lpMsgBuf = NULL;

        FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER | 
                      FORMAT_MESSAGE_FROM_SYSTEM |
                      FORMAT_MESSAGE_IGNORE_INSERTS,
                      NULL,
                      GetLastError(),
                      MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
                      (LPTSTR) &lpMsgBuf,
                      0, NULL );

        wprintf_s(szErrMsg );
        wprintf_s(lpMsgBuf);
        bRetCode = FALSE;

        LocalFree(lpMsgBuf);
    }

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

    return bRetCode;
}

void main()
{
    //This query inserts a new record, reads the FILESTREAM path of the
    //inserted record and returns the current transaction context.

    TCHAR *sqlDBQuery =
       TEXT("INSERT INTO Archive.dbo.Records(Id, SerialNumber, Chart)")
       TEXT(" OUTPUT GET_FILESTREAM_TRANSACTION_CONTEXT(), inserted.Chart.PathName()")
       TEXT("VALUES (newid (), 35, 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 an ODBC User DSN has been created
         //with the following settings:
         //
         //Driver:      Sql Server Native Client 10.0
         //Name:        Sql Server FILESTREAM
         //Description: Sql Server FILESTREAM
         //Server: .
         //Change Default Database to: Archive

         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. The ODBC driver will not automatically
        //COMMIT the transaction it BEGIN if SQL_AUTOCOMMIT_OFF is set.

        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 srcFilePath[1024];
        SQLINTEGER cbsrcFilePath;

        if ( SQLGetData(hstmt, 2, SQL_C_TCHAR, srcFilePath, sizeof(srcFilePath), &cbsrcFilePath) != 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;

        //Update the FILESTREAM BLOB data from **Temp** to **Done**.
        if ( UpdateBLOB(srcFilePath,
            transactionToken,
            cbTransactionToken) == TRUE )
            mode = SQL_COMMIT;

        //Commit the TRANSACTION if the BLOB was successfully udpated;
        //ROLLBACK the TRANSACTION if it was not.
        SQLTransact(henv, hdbc, mode);
    }
    catch(ODBCErrors *pErrors)
    {
        pErrors->Print();
        delete pErrors;
    }

    //Free and clean up the ODBC data handles that were initially created.
    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);
}

Consulte también

Obtener acceso a los datos FILESTREAM con OpenSqlFilestream
Crear aplicaciones cliente para datos FILESTREAM