Esecuzione di aggiornamenti parziali di dati FILESTREAM
Un'applicazione utilizza FSCTL_SQL_FILESTREAM_FETCH_OLD_CONTENT per eseguire aggiornamenti parziali dei dati BLOB FILESTREAM. La funzione DeviceIoControl passa il valore e l'handle restituito da OpenSqlFilestream al driver FILESTREAM. Tramite il driver viene forzata una copia lato server dei dati FILESTREAM correnti nel file a cui fa riferimento l'handle. Se l'applicazione rilascia il valore FSCTL_SQL_FILESTREAM_FETCH_OLD_CONTENT dopo la scrittura nell'handle, l'ultima operazione di scrittura viene resa persistente, mentre quelle precedenti eseguite nell'handle vanno perse.
Nota
Per l'accesso remoto, FILESTREAM è basato sul protocollo SMB .
Esempio
Nell'esempio seguente viene illustrato come utilizzare il valore FSCTL_SQL_FILESTREAM_FETCH_OLD_CONTENT per eseguire un aggiornamento parziale di dati BLOB FILESTREAM inseriti.
Nota
Questo esempio richiede il database e la tabella abilitati per FILESTREAM creati in Creare un database abilitato per FILESTREAM e Creare una tabella per archiviare dati FILESTREAM.
#include <windows.h>
#include<sqlext.h>
#include <stdio.h>
#include <sqlncli.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 occured.
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);
}
Vedere anche
Accesso ai dati FILESTREAM con OpenSqlFilestream
Creazione di applicazioni client per dati FILESTREAM