Microsoft KB Archive/242249

= Saving an ADO Recordset to an IStream =

Article ID: 242249

Article Last Modified on 8/5/2004

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APPLIES TO


 * Microsoft ActiveX Data Objects 1.5
 * Microsoft ActiveX Data Objects 2.0
 * Microsoft ActiveX Data Objects 2.1
 * Microsoft ActiveX Data Objects 2.5
 * Microsoft ActiveX Data Objects 2.6
 * Microsoft ActiveX Data Objects 2.7

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This article was previously published under Q242249



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.

For performance or other reasons it may sometimes be desired to save an ADO recordset to the memory only as a stream of data. To accomplish that you can use the ADO recordset's IPersistStream interface implementation.



Saving an ADO Recordset Object
This sample uses the following steps to save an ADO recordset:


 * 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
Given the IStream object, the sample then recreates another ADO recordset from it. It does this using the IStream pointer that holds the data stream and calls OleLoadFromStream.

Below is the key code from the sample: 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;iFields->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(ppRS)))        ) return hr; }   catch (_com_error & e)    { return e.Error; }   return S_OK; } The following files are available for download from the Microsoft Download Center:

AdoPersist.exe

For additional information about how to download Microsoft Support files, click the following article number to view the article in the Microsoft Knowledge Base:

119591 How to Obtain Microsoft Support Files from Online Services

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