Set Large Data (OLE DB)

  • Article

This sample shows how to set BLOB data, create a table, add a sample record, fetches that record in the rowset, and then set the value of the BLOB field. This sample is not supported on IA64.

To pass a pointer to its own storage object, the consumer creates an accessor that binds the value of the BLOB column and then calls the IRowsetChange::SetData or IRowsetChange::InsertRow methods.

This sample requires the AdventureWorks sample database, which you can download from the Microsoft SQL Server Samples and Community Projects home page.

Security note Security Note

When possible, use Windows Authentication. If Windows Authentication is not available, prompt users to enter their credentials at run time. Avoid storing credentials in a file. If you must persist credentials, you should encrypt them with the Win32 crypto API.

Procedures

To set BLOB data

  1. Create a DBOBJECT structure describing how the BLOB column should be accessed. Set the dwFlag element of the DBOBJECT structure to STGM_READ and set the iid element to IID_ISequentialStream (the interface to be exposed).

  2. Set the properties in the DBPROPSET_ROWSET property group so the rowset is updatable.

  3. Create a set of bindings (one of each column) by using an array of DBBINDING structures. Set the wType element in the DBBINDING structure to DBTYPE_IUNKNOWN, and the pObject element to point to the DBOBJECT structure you created.

  4. Create an accessor using the binding information in the DBBINDINGS array of structures.

  5. Call GetNextRows to fetch next rows into the rowset. Call GetData to read the data from the rowset.

  6. To set the data, create a storage object containing the data (and also the length indicator), and then call IRowsetChange::SetData (or IRowsetChange::InsertRow) with the accessor that binds the BLOB column.

Example

Description

Compile with ole32.lib oleaut32.lib and execute the following C++ code listing. This application connects to your computer's default SQL Server instance. On some Windows operating systems, you will need to change (localhost) or (local) to the name of your SQL Server instance. To connect to a named instance, change the connection string from L"(local)" to L"(local)\\name" , where name is the named instance. By default, SQL Server Express installs to a named instance. Make sure your INCLUDE environment variable includes the directory that contains sqlncli.h.

Code

// 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;
}