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OriginalValue and UnderlyingValue Properties Example (VC++)

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.

// BeginOriginalValueCpp.cpp
// compile with: /EHsc
#import "msado15.dll" no_namespace rename("EOF", "EndOfFile")

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

// class extracts title_id and type from titles table
class CTitleRs : public CADORecordBinding {
   BEGIN_ADO_BINDING(CTitleRs)

   // 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;
};

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

int main() {
   if (FAILED(::CoInitialize(NULL)))
      return -1;

   OriginalValueX();
   ::CoUninitialize();
}

void OriginalValueX() {
   // 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
   CTitleRs titlers;   // C++ Class object
   char * token1;

   try {
      _bstr_t strCnn("Provider='sqloledb'; Data Source='My_Data_Source'; Initial Catalog='pubs'; Integrated Security='SSPI';");

      // Open connection.
      TESTHR(pConnection.CreateInstance(__uuidof(Connection)));
      pConnection->Open (strCnn, "", "", adConnectUnspecified);

      // 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 IDispatch type; convert to correct variant type.
      pRstTitles->Open("Titles", _variant_t((IDispatch *)pConnection,true),
         adOpenKeyset, adLockBatchOptimistic, adCmdTable);

      // Open IADORecordBinding interface pointer 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_s((char *)titlers.m_szau_Type, " ", &token1), "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("Data has changed!");

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

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

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

            printf("\nUnderlying Value: %s\n\n", (LPCSTR) (_bstr_t) pFldType->UnderlyingValue);
         }
         pRstTitles->MoveNext();
      }
   }
   catch (_com_error &e)  {
      // Notify the user of errors if any.
      // Pass a connection pointer accessed from the Connection.
      PrintProviderError(pConnection);
      PrintComError(e);
   }

   // Clean up objects before exit.  Release the IADORecordset Interface here   
   if (picRs)
      picRs->Release();

   if (pRstTitles)
      if (pRstTitles->State == adStateOpen) {
         // Cancel the update because this is a demonstration.
         pRstTitles->CancelBatch(adAffectAll);
         pRstTitles->Close();
      }
      if (pConnection)
         if (pConnection->State == adStateOpen) {
            // Restore Original Values.
            pConnection->Execute(strSQLRestore, NULL, 0);
            pConnection->Close();
         }
};

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);
      }
   }
}

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);
}
Data has changed!
Title ID: PS1372
Current Value: self_help   
Original Value: psychology  
Underlying Value: sociology   

Data has changed!
Title ID: PS2091
Current Value: self_help   
Original Value: psychology  
Underlying Value: sociology   

Data has changed!
Title ID: PS2106
Current Value: self_help   
Original Value: psychology  
Underlying Value: sociology   

Data has changed!
Title ID: PS3333
Current Value: self_help   
Original Value: psychology  
Underlying Value: sociology   

Data has changed!
Title ID: PS7777
Current Value: self_help   
Original Value: psychology  
Underlying Value: sociology   
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