将 ADO 记录集保存到一个 IStream

将 ADO 记录集保存到一个 IStream
ADO 1.5 x 和 2.x Recordset 实施提供了用于数据持久性到磁盘文件的两个函数：
若要将保存到文件中记录集对象 ADORecordset.Save()。
重新加载一个文件中的记录集 ADORecordset.Open()。
出于性能或其他原因它可能有时是所希望将 ADO 记录集保存到内存中，只能作为数据的流。若要完成的您可以使用 ADO 记录集的 IPersistStream 接口实现。

保存一个 ADO 记录集对象
此示例使用以下步骤来保存一个 ADO 记录集：
在给定的 ADO 记录集，获取一个指针到 IPersistStream 对象上调用 QueryInterface()。
若要创建一个标准，COM，IStream 对象使用 CreateStreamOnHGlobal()。
调用 COM 函数 OleSaveToStream() 将 IPersistStream 对象保存到 IStream 对象。
重新创建 ADO 记录集
重新指定 IStream 对象，该示例然后创建另一个 ADO 记录集从它。它执行此使用保存的数据流并调用 OleLoadFromStream() IStream 指针。

下面是键的代码示例中：


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)
{
    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, IStream* * ppStream)
{
    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, IStreamPtr pStream)
{
    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;
}

_StreamPtr pStreamTest = NULL;
		_bstr_t        strPath("D:/1.txt");
		_bstr_t        strOpen("");

		_variant_t    varBLOB;
		_variant_t  varOptional(DISP_E_PARAMNOTFOUND, VT_ERROR);
		HRESULT hr = pStreamTest.CreateInstance(__uuidof(Stream));
		if(FAILED(hr))
		{
			return;
		}
		pStreamTest->Type = adTypeBinary;
		hr = pStreamTest->Open(varOptional, adModeUnknown, adOpenStreamUnspecified, strOpen, strOpen);
		mm->Save(pStreamTest.GetInterfacePtr(), adPersistADTG);
		pStreamTest->SaveToFile("d:\\1.txt", adSaveCreateOverWrite);
			//pStreamTest->put_Position(0);
			//pStreamTest->LoadFromFile(strPath);
			/*pStreamTest->WriteText("adsf", adWriteChar);*/
		HGLOBAL hGlobal = GlobalAlloc(GMEM_MOVEABLE, pStreamTest->GetSize());
		LPVOID pvData = NULL;
		IStream *ps;
		//CString s = pStreamTest->ReadText(adReadAll);
		//MessageBox(s);
		
		varBLOB = pStreamTest->Read(adReadAll);
		if (hGlobal != NULL)
		{
			if ((pvData = GlobalLock(hGlobal)) != NULL)
			{
				int aa = pStreamTest->GetSize() + 1;
				//char * m_pBMPBuffer = new char[pStreamTest->GetSize() + 1];//分配必要的存储空间
				char *pBuf = NULL;
				HRESULT hr1 =SafeArrayAccessData(varBLOB.parray, (void **)&pBuf);
				memcpy(pvData, pBuf, pStreamTest->GetSize()); //复制数据到缓冲 区 m_pBMPBuffer
				SafeArrayUnaccessData(varBLOB.parray);
				GlobalUnlock(hGlobal);
				CreateStreamOnHGlobal(hGlobal, TRUE, &ps);
			}
		}

将 ADO 记录集保存到一个 IStream

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