More nvarchar(max) columns in one table

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More nvarchar(max) columns in one table

wenna.geyer

SSC Journeyman

Points: 89
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April 12, 2010 at 7:06 am

#213641

Hi,
I am using MS SQL 2008 and the MS SQL native client ole db interface. My program is writen in C++.
I have more than one nvarchar(max) columns in one table. I would like to read them. Accoding to MS SQL help, I should use the ISequentialStream Interface. That works also for one column. But if there are more than one columns in a table, it doesnot work any more. Does anyone know how can I fix it?
Many thanks!

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sevans-1026766 SSC Enthusiast Points: 102 More actions · Answer 1

wenna.geyer (4/12/2010)
Hi,
I am using MS SQL 2008 and the MS SQL native client ole db interface. My program is writen in C++.
I have more than one nvarchar(max) columns in one table. I would like to read them. Accoding to MS SQL help, I should use the ISequentialStream Interface. That works also for one column. But if there are more than one columns in a table, it doesnot work any more. Does anyone know how can I fix it?
Many thanks!

Hard to say without seeing your source code, how about using multiple instances of ISequentialStream?

wenna.geyer SSC Journeyman Points: 89 More actions · Answer 2

Sorry, there is too much code. Here is just a part of the IAccessor of the columns and the IOpenRowset for the results.

HRESULT hr = p_pIRowset->QueryInterface(IID_IColumnsInfo, (void **)&pIColumnsInfo);

if (SUCCEEDED(hr))

{

// Retrieve the column information.

pIColumnsInfo->GetColumnInfo(&dwNumCols, &pDBColumnInfo, &pStringsBuffer);

// Free the column information interface.

//pIColumnsInfo->Release();

pIColumnsInfo = NULL;

SQL_ACCESSOR sColAccessor;

sColAccessor.m_ulOffset = 0;

std::vector<DBBINDING> rgBindings4Col;

rgBindings4Col.reserve(dwNumCols);

// Using the ColumnInfo structure, fill out the pBindings array.

for (DWORD dwColumn = 0 ; dwColumn < dwNumCols ; dwColumn ++ )

{

rgBindings4Col[dwColumn].iOrdinal = pDBColumnInfo[dwColumn].iOrdinal;

rgBindings4Col[dwColumn].dwPart = DBPART_VALUE | DBPART_LENGTH| DBPART_STATUS;

rgBindings4Col[dwColumn].dwMemOwner = DBMEMOWNER_CLIENTOWNED;

rgBindings4Col[dwColumn].eParamIO = DBPARAMIO_NOTPARAM;

rgBindings4Col[dwColumn].pBindExt = NULL;

rgBindings4Col[dwColumn].bPrecision = pDBColumnInfo[dwColumn].bPrecision;

rgBindings4Col[dwColumn].bScale = pDBColumnInfo[dwColumn].bScale;

rgBindings4Col[dwColumn].pTypeInfo = NULL;

rgBindings4Col[dwColumn].dwFlags = 0;

if(DBTYPE_IUNKNOWN == pDBColumnInfo[dwColumn].wType ||

(pDBColumnInfo[dwColumn].dwFlags & DBCOLUMNFLAGS_ISLONG) )

{

// Create the DBBINDING, requesting a storage-object pointer from

// The SQL Server Native Client OLE DB provider.

rgBindings4Col[dwColumn].pObject = (DBOBJECT *)CoTaskMemAlloc(sizeof(DBOBJECT));

// Set up the DBOBJECT structure.

rgBindings4Col[dwColumn].pObject->dwFlags = STGM_READ;

rgBindings4Col[dwColumn].pObject->iid = IID_ISequentialStream;

rgBindings4Col[dwColumn].cbMaxLen = sizeof(ISequentialStream *);

rgBindings4Col[dwColumn].wType = DBTYPE_IUNKNOWN;

}

else

{

rgBindings4Col[dwColumn].wType = pDBColumnInfo[dwColumn].wType;

rgBindings4Col[dwColumn].cbMaxLen = (pDBColumnInfo[dwColumn].wType == DBTYPE_WSTR) ? (pDBColumnInfo[dwColumn].ulColumnSize + 1) * sizeof(WCHAR) : pDBColumnInfo[dwColumn].ulColumnSize;

}

rgBindings4Col[dwColumn].obStatus = sColAccessor.m_ulOffset;

sColAccessor.m_ulOffset += sizeof(DBSTATUS);

rgBindings4Col[dwColumn].obLength = sColAccessor.m_ulOffset;

sColAccessor.m_ulOffset += sizeof(ULONG);

rgBindings4Col[dwColumn].obValue = sColAccessor.m_ulOffset;

sColAccessor.m_ulOffset += rgBindings4Col[dwColumn].cbMaxLen;

}

// Get the IAccessor interface.

if(m_vecColumnAccessor.size()<=p_dwRowsetNum)

{

//save the IAccessor interface in the vector for future use

m_vecColumnAccessor.push_back(sColAccessor);

hr = p_pIRowset->QueryInterface(IID_IAccessor, (void **) &sColAccessor.m_pIAccessor);

if (SUCCEEDED(hr) && sColAccessor.m_pIAccessor)

{

// Create an accessor from the set of bindings (pBindings).

hr = sColAccessor.m_pIAccessor->CreateAccessor(DBACCESSOR_ROWDATA, dwNumCols, &rgBindings4Col[0], sColAccessor.m_ulOffset, &sColAccessor.m_hAccessor, NULL);

if(SUCCEEDED(hr))

{

BYTE * pBuffer = new BYTE[m_vecColumnAccessor[p_dwRowsetNum].m_ulOffset];

HROW* hRows = new HROW[dwNumRows2Get];

HROW* pRows = &hRows[0];

hr = p_pIRowset->GetNextRows(DB_NULL_HCHAPTER, lRowOffset, dwNumRows2Get, &dwNumRowsRetrieved, &pRows);

for ( DWORD j = 0 ; j < dwNumRowsRetrieved ; j++ )

{

// Get the row data values.

hr2 = p_pIRowset->GetData(hRows[j], m_vecColumnAccessor[p_dwNumOfRows].m_hAccessor, pBuffer);

here it returns E_NOINTERFACE