IsolationLevel and Mode Properties Example (VC++)

This example uses the Mode property to open an exclusive connection, and the IsolationLevel property to open a transaction that is conducted in isolation of other transactions.

Example

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

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

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

   // Column title is the 2nd field in the table  
    ADO_VARIABLE_LENGTH_ENTRY2(2, adVarChar, m_szau_Title, sizeof(m_szau_Title), lau_TitleStatus, FALSE)  

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

public:  
   CHAR m_szau_Title[81];  
   ULONG lau_TitleStatus;  
   CHAR m_szau_Type[13];  
   ULONG lau_TypeStatus;  
};  

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

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

   IsolationLevelX();  

   ::CoUninitialize();  
}  

void IsolationLevelX() {  
   // Define ADO ObjectPointers.  Initialize Pointers on define.  These are in the ADODB :: namespace.  
   _RecordsetPtr  pRstTitles  = NULL;  
   _ConnectionPtr pConnection = NULL;  

   // Define other Variables  
   HRESULT hr = S_OK;  
   IADORecordBinding *picRs = NULL;   // Interface Pointer Declared  
   CTitleRs titlers;   // C++ Class Object  
   LPSTR p_TempStr = NULL;  
   char * token1;  

   // Assign Connection String to Variable  
   _bstr_t strCnn("Provider='sqloledb'; Data Source='My_Data_Source'; Initial Catalog='pubs'; Integrated Security='SSPI';");  

   try {  
      // Open Connection and Titles Table  
      TESTHR(pConnection.CreateInstance(__uuidof(Connection)));  
      pConnection->Mode = adModeShareExclusive;  
      pConnection->IsolationLevel = adXactIsolated;  
      pConnection->Open(strCnn,"", "", adConnectUnspecified);  

      TESTHR(pRstTitles.CreateInstance(__uuidof(Recordset)));  
      pRstTitles->CursorType = adOpenDynamic;  
      pRstTitles->LockType = adLockPessimistic;  

      pRstTitles->Open("titles", _variant_t((IDispatch*) pConnection, true),  
                       adOpenDynamic, adLockPessimistic, adCmdTable);  

      pConnection->BeginTrans();  

      // Display Connection Mode  
      if (pConnection->Mode == adModeShareExclusive)  
         printf("Connection Mode Is Exclusive");  
      else  
         printf("Connection Mode Is Not Exclusive");       

      // Display Isolation Level   
      if (pConnection->IsolationLevel == adXactIsolated)  
         printf("\nTransaction is Isolated\n");  
      else  
         printf("\nTransaction is not Isolated\n");  

      // Open an IADORecordBinding interface pointer which we will 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));  

      // Change the type of psychology titles.  
      p_TempStr = (LPSTR) malloc(sizeof(titlers.m_szau_Type));  

      while (!(pRstTitles->EndOfFile)) {  
         // Set the final character of the destination string to NULL.  
         p_TempStr[sizeof(titlers.m_szau_Type) - 1] = '\0';  

         // The source string will get truncated if its length is   
         // longer than the length of the destination string minus one.  
         strncpy_s(p_TempStr, sizeof(titlers.m_szau_Type), strtok_s(titlers.m_szau_Type, " ", &token1), sizeof(titlers.m_szau_Type) - 1);  

         // Compare type with psychology  
         if (!strcmp(p_TempStr,"psychology")) {  
            // Set the final character of the destination string to NULL.  
            titlers.m_szau_Type[sizeof(titlers.m_szau_Type) - 1] = '\0';  

            // Copy "self_help" title field.  The source string will get truncated if its length is   
            // longer than the length of the destination string minus one.  
            strncpy_s(titlers.m_szau_Type, sizeof(titlers.m_szau_Type), "self_help", sizeof(titlers.m_szau_Type) - 1);  
            picRs->Update(&titlers);  
         }  
         pRstTitles->MoveNext();  
      }  

      // Print current data in recordset.  
      pRstTitles->Requery(adOptionUnspecified);  

      // Open again IADORecordBinding interface pointer for Binding   
      // Recordset to a class.  
      TESTHR(pRstTitles->QueryInterface(__uuidof(IADORecordBinding), (LPVOID*)&picRs));  

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

      // Move to the first record of the title table  
      pRstTitles->MoveFirst();  

      // Clear the screen for the next display  
      // system("cls");  

      while (!pRstTitles->EndOfFile) {  
         printf("%s -  %s\n",titlers.lau_TitleStatus == adFldOK ?   
            titlers.m_szau_Title :"<NULL>",  
            titlers.lau_TypeStatus == adFldOK ?   
            titlers.m_szau_Type :"<NULL>");  
         pRstTitles->MoveNext();  
      }  
   }  
   catch(_com_error &e) {  
      // Notify the user of errors if any.  
      PrintProviderError(pConnection);  
      PrintComError(e);  
   }  

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

   if (pRstTitles)  
      if (pRstTitles->State == adStateOpen)  
         pRstTitles->Close();  

   if (pConnection)  
      if (pConnection->State == adStateOpen) {  
         // Restore Original Data  
         pConnection->RollbackTrans();  

         pConnection->Close();  
      }  

   // Deallocate the memory  
   if (p_TempStr)  
      free(p_TempStr);  
}  

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, (LPCSTR) 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);  
}  

Connection Mode Is Exclusive
Transaction is Isolated
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See Also

IsolationLevel Property
Mode Property (ADO)