Impostare dati di grandi dimensioni (OLE DB)

Articolo
05/07/2013

In questo esempio viene illustrato come impostare dati BLOB, creare una tabella, aggiungere un record di esempio, recuperare tale record nel set di righe e quindi impostare il valore del campo BLOB. Questo esempio non è supportato in IA64.

Per passare un puntatore al relativo oggetto di archiviazione, il consumer crea una funzione di accesso che associa il valore della colonna BLOB e quindi chiama il metodo IRowsetChange::SetData o IRowsetChange::InsertRow.

Per l'esempio è necessario il database di esempio AdventureWorks, che è possibile scaricare dalla home page del sito relativo a progetti della community ed esempi per Microsoft SQL Server.

Nota sulla sicurezza
Se possibile, utilizzare l'autenticazione di Windows. Se l'autenticazione di Windows non è disponibile, agli utenti verrà richiesto di immettere le credenziali in fase di esecuzione. Evitare di archiviare le credenziali in un file. Se è necessario rendere persistenti le credenziali, è consigliabile crittografarle utilizzando l'API di crittografia Win32.

Procedure

Per impostare dati BLOB

Creare una struttura DBOBJECT che descrive il modo in cui accedere alla colonna BLOB. Impostare l'elemento dwFlag della struttura DBOBJECT su STGM_READ e impostare l'elemento iid su IID_ISequentialStream, ovvero l'interfaccia da esporre.
Impostare le proprietà nel gruppo di proprietà DBPROPSET_ROWSET in modo che il set di righe sia aggiornabile.
Creare un set di associazioni, uno per ogni colonna, utilizzando una matrice di strutture DBBINDING. Impostare l'elemento wType nella struttura DBBINDING su DBTYPE_IUNKNOWN e l'elemento pObject in modo che punti alla struttura DBOBJECT creata.
Creare una funzione di accesso utilizzando le informazioni di associazione nella matrice di strutture DBBINDINGS.
Chiamare GetNextRows per recuperare le righe successive nel set di righe. Chiamare GetData per leggere i dati dal set di righe.
Per impostare i dati, creare un oggetto di archiviazione contenente i dati (e anche l'indicatore di lunghezza) e quindi chiamare IRowsetChange::SetData (o IRowsetChange::InsertRow) con la funzione di accesso che associa la colonna BLOB.

Esempio

Descrizione

Compilare il listato di codice C++ seguente con ole32.lib oleaut32.lib ed eseguirlo. In questa applicazione viene eseguita la connessione all'istanza predefinita di SQL Server nel computer in uso. In alcuni sistemi operativi Windows sarà necessario modificare (local) o (localhost) impostando il valore sul nome dell'istanza di SQL Server. Per connettersi a un'istanza denominata, modificare la stringa di connessione da L"(local)" in L"(local)\\nome", dove nome rappresenta l'istanza denominata. Per impostazione predefinita, SQL Server Express viene installato in un'istanza denominata. Verificare che nella variabile di ambiente INCLUDE sia presente la directory che contiene sqlncli.h.

Codice

// compile with: ole32.lib oleaut32.lib
#define UNICODE
#define DBINITCONSTANTS
#define INITGID
#define OLEDBVER 0x0250  // to include correct interfaces

#include <windows.h>
#include <stdio.h>
#include <stddef.h>
#include <iostream>
#include <oledb.h>
#include <oledberr.h>
#include <SQLNCLI.h>

using namespace std;

#define SAFE_RELEASE(pIUnknown) if(pIUnknown) (pIUnknown)->Release();
HRESULT GetCommandObject(REFIID riid, IUnknown** ppIUnknown);
HRESULT CreateTable(ICommandText* pICommandText);

class CSeqStream : public ISequentialStream {
public:
   // Constructors
   CSeqStream();
   virtual ~CSeqStream();

   virtual BOOL Seek(ULONG iPos);
   virtual BOOL Clear();
   virtual BOOL CompareData(void* pBuffer);
   virtual ULONG Length() { return m_cBufSize; };

   virtual operator void* const() { return m_pBuffer; };

   STDMETHODIMP_(ULONG) AddRef(void);
   STDMETHODIMP_(ULONG) Release(void);
   STDMETHODIMP QueryInterface(REFIID riid, LPVOID *ppv);

   STDMETHODIMP Read( 
      /* [out] */ void __RPC_FAR *pv,
      /* [in]  */ ULONG cb,
      /* [out] */ ULONG __RPC_FAR *pcbRead);

   STDMETHODIMP Write( 
      /* [in] */ const void __RPC_FAR *pv,
      /* [in] */ ULONG cb,
      /* [out]*/ ULONG __RPC_FAR *pcbWritten);

private:
   ULONG m_cRef;   // reference count
   void* m_pBuffer;   // buffer
   ULONG m_cBufSize;   // buffer size
   ULONG m_iPos;   // current index position in the buffer
};

// class implementation
CSeqStream::CSeqStream() {
   m_iPos = 0;
   m_cRef = 0;
   m_pBuffer = NULL;
   m_cBufSize = 0;

   // The constructor AddRef's
   AddRef();
}

CSeqStream::~CSeqStream() {
   // Shouldn't have any references left ASSERT(m_cRef == 0);
   CoTaskMemFree(m_pBuffer);
}

ULONG CSeqStream::AddRef() {
   return ++m_cRef;
}

ULONG CSeqStream::Release() {
   // ASSERT(m_cRef);
   if (--m_cRef)
      return m_cRef;

   delete this;
   return 0;
}

HRESULT CSeqStream::QueryInterface(REFIID riid, void** ppv) {
   // ASSERT(ppv);
   *ppv = NULL;

   if (riid == IID_IUnknown)
      *ppv = this;

   if (riid == IID_ISequentialStream)
      *ppv = this;

   if(*ppv) {
      ((IUnknown*)*ppv)->AddRef();
      return S_OK;
   }

   return E_NOINTERFACE;
}

BOOL CSeqStream::Seek(ULONG iPos) {
   // Make sure the desired position is within the buffer
   // ASSERT(iPos == 0 || iPos < m_cBufSize);

   // Reset the current buffer position
   m_iPos = iPos;
   return TRUE;
}

BOOL CSeqStream::Clear() {
   // Frees the buffer
   m_iPos = 0;
   m_cBufSize = 0;

   CoTaskMemFree(m_pBuffer);
   m_pBuffer = NULL;

   return TRUE;
}

BOOL CSeqStream::CompareData(void* pBuffer) {
   // ASSERT(pBuffer);

   // Quick and easy way to compare user buffer with the stream
   return memcmp(pBuffer, m_pBuffer, m_cBufSize) == 0;
}

HRESULT CSeqStream::Read(void *pv, ULONG cb, ULONG* pcbRead) {
   // Parameter checking
   if (pcbRead)
      *pcbRead = 0;

   if (!pv)
      return STG_E_INVALIDPOINTER;

   if (cb == 0)
      return S_OK;

   // Actual code
   ULONG cBytesLeft = m_cBufSize - m_iPos;
   ULONG cBytesRead = cb > cBytesLeft ? cBytesLeft : cb;

   // if no more bytes to retrieve return 
   if (cBytesLeft == 0)
      return S_FALSE; 

   // Copy to users buffer the number of bytes requested or remaining
   memcpy(pv, (void*)((BYTE*)m_pBuffer + m_iPos), cBytesRead);
   m_iPos += cBytesRead;

   if (pcbRead)
      *pcbRead = cBytesRead;

   if (cb != cBytesRead)
      return S_FALSE; 

   return S_OK;
}

HRESULT CSeqStream::Write(const void *pv, ULONG cb, ULONG* pcbWritten) {
   // Parameter checking
   if (!pv)
      return STG_E_INVALIDPOINTER;

   if (pcbWritten)
      *pcbWritten = 0;

   if (cb == 0)
      return S_OK;

   // Enlarge the current buffer
   m_cBufSize += cb;

   // Need to append to the end of the stream
   m_pBuffer = CoTaskMemRealloc(m_pBuffer, m_cBufSize);
   memcpy((void*)((BYTE*)m_pBuffer + m_iPos), pv, cb);
   // m_iPos += cb;

   if (pcbWritten)
      *pcbWritten = cb;

   return S_OK;
}

int main() {
   CoInitialize(NULL);

   DBOBJECT ObjectStruct;
   ObjectStruct.dwFlags = STGM_READ;
   ObjectStruct.iid = IID_ISequentialStream;

   struct BLOBDATA {
      DBSTATUS dwStatus;   
      DBLENGTH dwLength; 
      ISequentialStream* pISeqStream;
   };

   BLOBDATA BLOBGetData;
   BLOBDATA BLOBSetData;

   const ULONG cBindings = 1;
   DBBINDING rgBindings[cBindings]; 
   HRESULT hr = S_OK;

   IAccessor* pIAccessor = NULL;
   ICommandText* pICommandText = NULL;
   ICommandProperties* pICommandProperties = NULL;
   IRowsetChange* pIRowsetChange = NULL;
   IRowset* pIRowset = NULL;
   CSeqStream* pMySeqStream = NULL;

   DBCOUNTITEM cRowsObtained = 0;
   HACCESSOR hAccessor = DB_NULL_HACCESSOR;
   DBBINDSTATUS rgBindStatus[cBindings];
   HROW* rghRows = NULL;

   const ULONG cPropSets = 1;
   DBPROPSET rgPropSets[cPropSets];
   const ULONG cProperties = 1;
   DBPROP rgProperties[cProperties];
   const ULONG cBytes = 10;

   BYTE pBuffer[cBytes];
   ULONG cBytesRead = 0;

   BYTE pReadData[cBytes];   // read BLOB data in this array
   memset(pReadData, 0xAA, cBytes);

   BYTE pWriteData[cBytes];   // write BLOB data from this array
   memset(pWriteData, 'D', cBytes);

   // Get Command object
   hr = GetCommandObject(IID_ICommandText, (IUnknown**)&pICommandText);
   if (FAILED(hr)) {
      printf("Failed to get ICommandText interface.\n");
      // Release any references and return.
      goto Exit;
   }

   // Create table with image column and index
   hr = CreateTable(pICommandText);
   if (FAILED(hr)) {
      printf("Failed to create table.\n");
      // Release any references and return.
      goto Exit;
   }

   // Set the DBPROPSET structure.  It is used to pass an array 
   // of DBPROP structures to SetProperties().
   rgPropSets[0].guidPropertySet = DBPROPSET_ROWSET;
   rgPropSets[0].cProperties = cProperties;
   rgPropSets[0].rgProperties = rgProperties;

   // Now set properties in the property group (DBPROPSET_ROWSET)
   rgPropSets[0].rgProperties[0].dwPropertyID = DBPROP_UPDATABILITY;
   rgPropSets[0].rgProperties[0].dwOptions = DBPROPOPTIONS_REQUIRED;
   rgPropSets[0].rgProperties[0].dwStatus = DBPROPSTATUS_OK;
   rgPropSets[0].rgProperties[0].colid = DB_NULLID;
   rgPropSets[0].rgProperties[0].vValue.vt = VT_I4;
   V_I4(&rgPropSets[0].rgProperties[0].vValue) = DBPROPVAL_UP_CHANGE;

   // Set the rowset properties
   hr = pICommandText->QueryInterface(IID_ICommandProperties,
      (void **)&pICommandProperties);

   if (FAILED(hr)) {
      printf("Failed to get ICommandProperties to set rowset properties.\n");
      // Release any references and return.
      goto Exit;
   }

   hr = pICommandProperties->SetProperties(cPropSets, rgPropSets);

   if (FAILED(hr)) {
      printf("Execute failed to set rowset properties.\n");
      // Release any references and return.
      goto Exit;
   }

   // Execute a command (SELECT * FROM TestISeqStream)
   hr = pICommandText->SetCommandText(DBGUID_DBSQL, L"SELECT * FROM TestISeqStream");

   if (FAILED(hr)) {
      printf("Failed to set command text SELECT * FROM.\n");
      // Release any references and return.
      goto Exit;
   }

   hr = pICommandText->Execute(NULL, 
      IID_IRowsetChange, 
      NULL, 
      NULL,
      (IUnknown**)&pIRowsetChange);

   if (FAILED(hr)) {
      printf("Failed to execute the command SELECT * FROM.\n");
      // Release any references and return.
      goto Exit;
   }

   // Fill the DBBINDINGS array.
   rgBindings[0].iOrdinal = 2;   // ordinal position
   rgBindings[0].obValue = offsetof(BLOBDATA, pISeqStream);
   rgBindings[0].obLength = offsetof(BLOBDATA, dwLength);
   rgBindings[0].obStatus = offsetof(BLOBDATA, dwStatus);
   rgBindings[0].pTypeInfo = NULL;
   rgBindings[0].pObject = &ObjectStruct;
   rgBindings[0].pBindExt = NULL;
   rgBindings[0].dwPart =  DBPART_VALUE | DBPART_STATUS | DBPART_LENGTH;
   rgBindings[0].dwMemOwner = DBMEMOWNER_CLIENTOWNED;
   rgBindings[0].eParamIO = DBPARAMIO_NOTPARAM;
   rgBindings[0].cbMaxLen = 0; 
   rgBindings[0].dwFlags = 0;
   rgBindings[0].wType = DBTYPE_IUNKNOWN;
   rgBindings[0].bPrecision = 0;
   rgBindings[0].bScale = 0;

   // Create an accessor using the binding information.
   hr = pIRowsetChange->QueryInterface(IID_IAccessor, (void**)&pIAccessor);
   if (FAILED(hr)) {
      printf("Failed to get IAccessor interface.\n");
      // Release any references and return.
      goto Exit;
   }

   hr = pIAccessor->CreateAccessor(DBACCESSOR_ROWDATA,
      cBindings,
      rgBindings, 
      sizeof(BLOBDATA),
      &hAccessor,
      rgBindStatus);

   if (FAILED(hr)) {
      printf("Failed to create an accessor.\n");
      // Release any references and return.
      goto Exit;
   }

   // get the first row.
   hr = pIRowsetChange->QueryInterface(IID_IRowset, (void **)&pIRowset);
   if (FAILED(hr)) {
      printf("Failed to get IRowset interface.\n");
      // Release any references and return.
      goto Exit;
   }

   hr = pIRowset->GetNextRows(NULL, 0, 1, &cRowsObtained, &rghRows);
   hr = pIRowset->GetData(rghRows[0], hAccessor, &BLOBGetData);

   // Verify the retrieved data, only if data is not null.
   if (BLOBGetData.dwStatus == DBSTATUS_S_ISNULL) {
      // Process null data
      printf("Provider returned a null value.\n");
   } 
   else if(BLOBGetData.dwStatus == DBSTATUS_S_OK) {
      // Provider returned a nonNULL value
      BLOBGetData.pISeqStream->Read( pBuffer, cBytes, &cBytesRead);

      if (memcmp(pBuffer, pReadData, cBytes) != 0) {
         // cleanup 
      }

      SAFE_RELEASE(BLOBGetData.pISeqStream);
   }

   // Set up data for SetData.
   pMySeqStream = new CSeqStream();

   // Put data into ISequentialStream object for the provider to write.
   pMySeqStream->Write(pWriteData, cBytes, NULL);

   BLOBSetData.pISeqStream = (ISequentialStream*)pMySeqStream;
   BLOBSetData.dwStatus = DBSTATUS_S_OK;
   BLOBSetData.dwLength = pMySeqStream->Length();

   // Set the data.
   hr = pIRowsetChange->SetData(rghRows[0], hAccessor, &BLOBSetData);
   if (FAILED(hr))     {
      printf("Failed to set data.\n");
      // Release any references and return.
      goto Exit;
   }

   hr = pIAccessor->ReleaseAccessor(hAccessor, NULL);
   if (FAILED(hr)) {
      printf("Failed to release accessor.\n");
      // Release any references and return.
      goto Exit;
   }

   hr = pIRowset->ReleaseRows(cRowsObtained, rghRows, NULL, NULL, NULL);

   if (FAILED(hr)) {
      printf("Failed to release rows.\n");
      // Release any references and return.
      goto Exit;
   }

Exit:
   // Release all allocated memory and release interface pointers.
   CoUninitialize();
}

HRESULT GetCommandObject(REFIID riid, IUnknown** ppIUnknown) {
   HRESULT hr = S_OK;

   // Local interface pointers, until a connection is made.
   IDBInitialize* pIDBInitialize = NULL;
   IDBProperties*  pIDBProperties = NULL;
   IDBCreateSession* pIDBCreateSession = NULL;
   IDBCreateCommand* pIDBCreateCommand = NULL;

   const ULONG cPropSets = 1;
   DBPROPSET rgPropSets[cPropSets];

   const ULONG cProperties = 4;
   DBPROP rgProperties[cProperties];

   // Initialize property values needed to establish connection.
   for ( ULONG i = 0 ; i < 4 ; i++ )
      VariantInit(&rgProperties[i].vValue);

   // Server name.
   rgProperties[0].dwPropertyID = DBPROP_INIT_DATASOURCE;
   rgProperties[0].vValue.vt = VT_BSTR;

   rgProperties[0].vValue.bstrVal = SysAllocString(L"(local)");
   rgProperties[0].dwOptions = DBPROPOPTIONS_REQUIRED;
   rgProperties[0].colid = DB_NULLID;

   // Database.
   rgProperties[1].dwPropertyID = DBPROP_INIT_CATALOG;
   rgProperties[1].vValue.vt = VT_BSTR;
   rgProperties[1].vValue.bstrVal = SysAllocString(L"AdventureWorks");
   rgProperties[1].dwOptions = DBPROPOPTIONS_REQUIRED;
   rgProperties[1].colid = DB_NULLID;

   rgProperties[2].dwPropertyID = DBPROP_AUTH_INTEGRATED;
   rgProperties[2].vValue.vt = VT_BSTR;
   rgProperties[2].vValue.bstrVal = SysAllocString(L"SSPI");
   rgProperties[2].dwOptions = DBPROPOPTIONS_REQUIRED;
   rgProperties[2].colid = DB_NULLID;

   // Properties are now set.  Next, construct DBPROPSET structure (rgInitPropSet) used to pass an 
   // array of DBPROP structures (InitProperties) to the SetProperties method.
   rgPropSets[0].guidPropertySet = DBPROPSET_DBINIT;
   rgPropSets[0].cProperties = cProperties;
   rgPropSets[0].rgProperties = rgProperties;

   // Get the IDBInitialize interface.
   hr = CoCreateInstance(CLSID_SQLNCLI11, 
      NULL, 
      CLSCTX_INPROC_SERVER,
      IID_IDBInitialize, 
      (void**)&pIDBInitialize);

   if (FAILED(hr)) {
      printf("Failed to get IDBInitialize interface.\n");
      // Release any references and return.
      goto Exit;
   }

   // Set initialization properties.
   hr = pIDBInitialize->QueryInterface(IID_IDBProperties, (void **)&pIDBProperties);
   if (FAILED(hr)) {
      printf("Failed to get IDBProperties interface.\n");
      // Release any references and return.
      goto Exit;
   }

   hr = pIDBProperties->SetProperties(cPropSets, rgPropSets);
   if (FAILED(hr)) {
      printf("Failed to set properties for DBPROPSET_DBINIT.\n");
      // Release any references and return.
      goto Exit;
   }

   hr = pIDBInitialize->Initialize();
   if (FAILED(hr)) {
      printf("Failed to initialize.\n");
      // Release any references and return.
      goto Exit;
   }

   // Create a session object.
   hr = pIDBInitialize->QueryInterface( IID_IDBCreateSession,
                                        (void **)&pIDBCreateSession);

   if (FAILED(hr)) {
      printf("Failed to get pIDBCreateSession interface.\n");
      // Release any references and return.
      goto Exit;
   }

   hr = pIDBCreateSession->CreateSession( NULL, IID_IDBCreateCommand, (IUnknown**)&pIDBCreateCommand);

   if (FAILED(hr)) {
      printf("Failed to create session object.\n");
      // Release any references and return.
      goto Exit;
   }

   // Get CommandText object
   hr = pIDBCreateCommand->CreateCommand( NULL, riid, (IUnknown**)ppIUnknown);

   if (FAILED(hr)) {
      printf("Failed to create CommandText object.\n");
      // Release any references and return.
      goto Exit;
   }

   return hr;

Exit:
   // Free up all allocated memory and release interface pointers.
   return hr;
}

HRESULT CreateTable(ICommandText* pICommandText) {
   HRESULT hr = S_OK;

   // drop the table "TestISeqStream" if the table exists.
   hr = pICommandText->SetCommandText( DBGUID_DBSQL, L"if object_id('TestISeqStream') is not null drop table TestISeqStream");
   if (FAILED(hr)) {
      printf("Failed to set command text DROP TABLE.\n");
      // Release any references and return.
      goto Exit;
   }

   hr = pICommandText->Execute(NULL, IID_NULL, NULL, NULL, NULL);
   if (FAILED(hr)) {
      printf("Failed to drop the table.\n");
      // Release any references and return.
      goto Exit;
   }

   // Create a new table.
   hr = pICommandText->SetCommandText(DBGUID_DBSQL, 
      L"CREATE TABLE TestISeqStream (col1 int,col2 image)");

   if (FAILED(hr)) {
      printf("Failed to set command text CREATE TABLE.\n");
      // Release any references and return.
      goto Exit;
   }

   hr = pICommandText->Execute(NULL, IID_NULL, NULL, NULL, NULL);
   if (FAILED(hr)) {
      printf("Failed to create table.\n");
      // Release any references and return.
      goto Exit;
   }

   // Insert one row into table.
   hr = pICommandText->SetCommandText(DBGUID_DBSQL,
      L"INSERT INTO TestISeqStream(col1,col2) VALUES (1,0xAAAAAAAAAAAAAAAAA)");
   if (FAILED(hr)) {
      printf("Failed to set command text INSERT INTO.\n");
      // Release any references and return.
      goto Exit;
   }

   hr = pICommandText->Execute(NULL, IID_NULL, NULL, NULL, NULL);

   if (FAILED(hr)) {
      printf("Failed to insert record in the table.\n");
      // Release any references and return.
      goto Exit;
   }

Exit:
   // Release all allocated memory and release interface pointers.
   return hr;
}

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