MDAC 2.5 SDK - ADO

OriginalValue and UnderlyingValue Properties Example (VC++)

See Also

This example demonstrates the OriginalValue and UnderlyingValue properties by displaying a message if a record's underlying data has changed during a Recordset batch update.

#import "c:\Program Files\Common Files\System\ADO\msado15.dll" \
    no_namespace rename("EOF", "EndOfFile")

#include <ole2.h>
#include <stdio.h>
#include <conio.h>
#include "OriginalValueX.h"

// Function declarations
inline void TESTHR(HRESULT x) {if FAILED(x) _com_issue_error(x);};
void OriginalValueX(void);
void PrintProviderError(_ConnectionPtr pConnection);
void PrintComError(_com_error &e);

///////////////////////////////////////////////////////////
//                                                       //
//      Main Function                                    //
//                                                       //
///////////////////////////////////////////////////////////

void main()
{
    if(FAILED(::CoInitialize(NULL)))
        return;

    OriginalValueX();

    ::CoUninitialize();
}

///////////////////////////////////////////////////////////
//                                                       //
//            OriginalValueX Function                    //
//                                                       //
///////////////////////////////////////////////////////////

void OriginalValueX(void) 
{
    // Define ADO object pointers.
    // Initialize pointers on define.
    // These are in the ADODB::  namespace.
    _ConnectionPtr   pConnection    = NULL;
     FieldPtr      pFldType   = NULL;
    _RecordsetPtr   pRstTitles   = NULL;

    // Define string variables.
    _bstr_t strSQLChange("UPDATE Titles SET Type = "
            "'sociology' WHERE Type = 'psychology'");
    _bstr_t strSQLRestore("UPDATE Titles SET Type = "
            "'psychology' WHERE Type = 'sociology'");

    // Define Other Variables
    HRESULT    hr = S_OK;
    IADORecordBinding   *picRs  = NULL;  //Interface Pointer declared
    CTitlesRs titlers;        // C++ Class object

    try 
    {
        _bstr_t strCnn("Provider=sqloledb;Data Source=srv;"
            "Initial Catalog=Pubs;User Id=sa;Password=;");
        
        // Open connection.
        TESTHR(pConnection.CreateInstance(__uuidof(Connection)));
        pConnection->Open (strCnn, "", "", NULL);
        
        // Open Recordset for batch update.
        TESTHR(pRstTitles.CreateInstance(__uuidof(Recordset)));
        pRstTitles->PutActiveConnection(
            _variant_t((IDispatch *)pConnection,true));
        pRstTitles->CursorType = adOpenKeyset;
        pRstTitles->LockType = adLockBatchOptimistic;
        
        // Cast Connection pointer to an IDispatch type so converted 
        // to correct type of variant.
        pRstTitles->Open("Titles", 
            _variant_t((IDispatch *)pConnection,true),
            adOpenKeyset, adLockBatchOptimistic, adCmdTable);

        //Open an IADORecordBinding interface pointer which 
        //we'll use for Binding Recordset to a class.
        TESTHR(pRstTitles->QueryInterface(
            __uuidof(IADORecordBinding),(LPVOID*)&picRs));

        //Bind the Recordset to a C++ Class here  
        TESTHR(picRs->BindToRecordset(&titlers));

        // Set field object variable for Type field.
        pFldType = pRstTitles->Fields->GetItem("type");

        // Change the type of psychology titles.
        while(!(pRstTitles->EndOfFile))
        {
            if (!strcmp(strtok((char *)titlers.m_szau_Type," "), 
                "psychology"))
            {
                pFldType->Value = "self_help";
            }
            pRstTitles->MoveNext();
        }

        // Simulate a change by another user by updating data
        // using a command string.
        pConnection->Execute(strSQLChange,NULL,0);

        // Check for changes.
        pRstTitles->MoveFirst();
        while(!(pRstTitles->EndOfFile))
        {
            if (strcmp(pFldType->OriginalValue.pcVal,
                pFldType->UnderlyingValue.pcVal))
            {
                printf("\n\nData has changed!");

                printf("\n\nTitle ID: %s",titlers.lau_Title_idStatus == 
                    adFldOK ? titlers.m_szau_Title_id : "<NULL>");

                printf("\n\nCurrent Value: %s",
                    (LPCSTR) (_bstr_t) pFldType->Value);
                printf("\n\nOriginal Value: %s",
                    (LPCSTR) (_bstr_t) pFldType->OriginalValue);

                printf("\n\nUnderlying Value: %s\n\n",
                    (LPCSTR) (_bstr_t) pFldType->UnderlyingValue);

                printf("Press any key to continue...");
                getch();

                system("cls");
            }
            pRstTitles->MoveNext();
        }

        // Cancel the update because this is a demonstration.
        pRstTitles->CancelBatch(adAffectAll);

        // Restore Original Values.
        pConnection->Execute(strSQLRestore,NULL,0);

        // Clean up objects before exit.
        pRstTitles->Close();
        pConnection->Close();

        //Release IADORecordset Interface
        if (picRs)
            picRs->Release();
    }

    catch (_com_error &e)
    {
        // Notify the user of errors if any.
        // Pass a connection pointer accessed from the Connection.
        PrintProviderError(pConnection);
        PrintComError(e);
    }
};

///////////////////////////////////////////////////////////
//                                                       //
//      PrintProviderError Function                      //
//                                                       //
///////////////////////////////////////////////////////////
void PrintProviderError(_ConnectionPtr pConnection)
{
    // Print Provider Errors from Connection object.
    // pErr is a record object in the Connection's Error collection.
    ErrorPtr    pErr  = NULL;

    if( (pConnection->Errors->Count) > 0)
    {
        long nCount = pConnection->Errors->Count;

        // Collection ranges from 0 to nCount -1.
        for(long i = 0;i < nCount;i++)
        {
            pErr = pConnection->Errors->GetItem(i);
            printf("\t Error number: %x\t%s", pErr->Number,
                pErr->Description);
        }
    }
}

///////////////////////////////////////////////////////////
//                                                       //
//      PrintComError Function                           //
//                                                       //
///////////////////////////////////////////////////////////
void PrintComError(_com_error &e)
{
   _bstr_t bstrSource(e.Source());
   _bstr_t bstrDescription(e.Description());

    // Print COM errors. 
   printf("Error\n");
   printf("\tCode = %08lx\n", e.Error());
   printf("\tCode meaning = %s\n", e.ErrorMessage());
   printf("\tSource = %s\n", (LPCSTR) bstrSource);
   printf("\tDescription = %s\n", (LPCSTR) bstrDescription);
}

OriginalValueX.h:

#include "icrsint.h"

//This class extracts title_id and type from Titles table
class CTitlesRs : public CADORecordBinding
{
BEGIN_ADO_BINDING(CTitlesRs)
        // Column title_id is the 1st field in the Recordset
        ADO_VARIABLE_LENGTH_ENTRY2(1, adVarChar, m_szau_Title_id,
            sizeof(m_szau_Title_id), lau_Title_idStatus, FALSE)

        // Column type is the 3rd field in the Recordset
        ADO_VARIABLE_LENGTH_ENTRY2(3, adVarChar, m_szau_Type,
            sizeof(m_szau_Type), lau_TypeStatus, TRUE)
END_ADO_BINDING()

public:
    CHAR m_szau_Title_id[7];
    ULONG lau_Title_idStatus;
    CHAR m_szau_Type[13];
    ULONG lau_TypeStatus;
};