Saving an ADO Recordset to an IStream

• ActiveX Data Objects (ADO), versions 1.5, 2.0, 2.1

SUMMARY

ADOPERSIST.exe is a Visual C++ sample that shows you how to save an ADO recordset to an IStream object and then reload another ADO recordset from it.

ADO 1.5x and 2.x Recordset implementation offers two functions for data persistance to a disk file:

1. ADORecordset.Save() to save the recordset object to a file.



2. ADORecordset.Open() to reload a recordset from a file.

MORE INFORMATION

Saving an ADO Recordset Object

1. Calls QueryInterface() on the given ADO recordset to get a pointer to the IPersistStream object.



2. Uses CreateStreamOnHGlobal() to create a standard, COM, IStream object.



3. Calls the COM function OleSaveToStream() to save the IPersistStream object into the IStream object.

Recreating the ADO Recordset

int main(int argc, char* argv[])
{
	InitOle oleinit;

	HRESULT hr=S_OK;
	_RecordsetPtr rs; //Recordset for Saving Data
	_RecordsetPtr rs2; //Recordset for Loading Data
	IStreamPtr pStream;

//----------------------------------------
//	Create a recordset for testing
//----------------------------------------
	if (FAILED(CreateTestRS(&rs)))
	{
		printf("Couldn't create the first recordset\n");
		goto exit;
	}

//----------------------------------------
//	Create IStream
//----------------------------------------
	if (FAILED(SaveRS(rs, (IStream**)&pStream)))
	{
		printf("Couldn't save the recordset\n");
		goto exit;
	}

//----------------------------------------
//	Load another recordset from IStream
//----------------------------------------
	if (FAILED(LoadRS(&rs2, pStream)))
	{
		printf("Couldn't save the recordset\n");
		goto exit;
	}
	//Now display the names of the fields of the rs that we just recreated
	{
		for (short i =0;i<rs2->Fields->Count;i++)
		printf("Name of field %d is %s\n", i, (LPCTSTR) rs2->Fields->GetItem(i)->Name);
	}



//----------------------------------------
//	Pause and then exit so that the user
//	Can  
//----------------------------------------

exit:
	printf("Press any key to end program\n");
	_getch();
	return 0;
}


//----------------------------------------
//	Create a recordset from scratch
//----------------------------------------

HRESULT CreateTestRS(_Recordset** prs/*OUT*/)
{
    try
    {
	* prs=NULL;
	_RecordsetPtr pRS;
	pRS.CreateInstance( __uuidof(Recordset));
	pRS->CursorLocation = adUseClient;
	pRS->CursorType = adOpenStatic;
	pRS->LockType = adLockBatchOptimistic;
	// append fields
	pRS->Fields->Append(_bstr_t("ADOField1"), adVarChar, 45,adFldFixed);
	pRS->Fields->Append(_bstr_t("ADOField2"), adBoolean, 0,adFldFixed);
	pRS->Fields->Append(_bstr_t("ADOField3"), adCurrency, 0,adFldFixed);
	pRS->Fields->Append(_bstr_t("ADOField4"), adDate, 0,adFldFixed);
	pRS->Open(vtMissing, vtMissing, adOpenStatic,adLockBatchOptimistic,-1);
	*prs= pRS.Detach();
    }
    catch (_com_error & e)
    {
	return e.Error();
    }
    return S_OK;
}

HRESULT SaveRS(_RecordsetPtr pRS/*IN*/, IStream* * ppStream/*OUT*/)
{
    HRESULT hr=S_OK;
    try
    {
	*ppStream=NULL;

        // QI and return IPersistStream
        IPersistStreamPtr pIPersist(pRS);
        if (pIPersist )
        {
            //Create a standard stream in memory
            if (FAILED(hr=CreateStreamOnHGlobal(0, TRUE, (IStream **)ppStream)))
		return hr;

            // Persist the pRS
            if (FAILED(hr=OleSaveToStream(pIPersist, *ppStream)))
		return hr;

        }
        else
            return E_NOINTERFACE;
    }
    catch (_com_error & e)
    {
	return e.Error();
    }
return S_OK;
    
}

HRESULT LoadRS(_Recordset* *ppRS/*OUT*/, IStreamPtr pStream/*IN*/)
{
    HRESULT hr=S_OK;
    try
    {
	*ppRS=NULL;
        if (NULL==pStream)
            return E_NOINTERFACE;
        // Load the pRS.
        LARGE_INTEGER li;
        li.QuadPart = 0;

	//Set the pointer to the beginning of the stream
        if (FAILED(hr=pStream->Seek(li, STREAM_SEEK_SET, 0)))
            return hr;

	if (FAILED(hr=OleLoadFromStream(pStream, 
        	__uuidof(_Recordset),
                reinterpret_cast<LPVOID *>(ppRS)))
		)
            return hr;
    }
    catch (_com_error & e)
    {
	return e.Error();
    }
    return S_OK;
} 

AdoPersist.exe

http://www.microsoft.com/downloads/search.asp

Additional query words:

Keywords : kbfile kbADO kbADO150 kbADO200 kbDatabase kbGrpVCDB
Version : WINDOWS:1.5,2.0,2.1
Platform : WINDOWS
Issue type : kbhowto