BeginTrans, CommitTrans, and RollbackTrans Methods Example (VC++)

This example changes the book type of all psychology books in the Titles table of the database. After the BeginTrans method starts a transaction that isolates all the changes made to the Titles table, the CommitTrans method saves the changes. You can use the Rollback method to undo changes that you saved using the Update method.

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

#include <stdio.h>
#include <ole2.h>
#include <conio.h>
#include <assert.h>
#include <malloc.h>
#include "BeginTransX.h"

inline void TESTHR(HRESULT x) {if FAILED(x) _com_issue_error(x);};
void BeginTransX(void);
void PrintProviderError(_ConnectionPtr pConnection);

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

    BeginTransX();

    //Wait here for user to see the output.
    printf("\nPress any key to continue...");
    getch();

    ::CoUninitialize();
}

///////////////////////////////////////////////////////////
//                                                       //
//      BeginTransX Function                             //
//                                                       //
///////////////////////////////////////////////////////////

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

    //Define Other Variables
    HRESULT hr = S_OK;  
    IADORecordBinding   *picRs = NULL;  //Interface Pointer declared...
    CTitlesRs titlrs;
    _bstr_t strTitle; 
    _bstr_t strMessage;
    LPSTR p_TempStr = NULL;
    char chKey;
    int i = 0;

    try 
    {
        // open connection.
        _bstr_t strCnn("Provider='sqloledb';Data Source='MySqlServer';"
            "Initial Catalog='pubs';Integrated Security='SSPI';");

        TESTHR(pConnection.CreateInstance(__uuidof(Connection)));

        TESTHR(pConnection->Open(strCnn,"","",adConnectUnspecified));

        rstTitles.CreateInstance(__uuidof(Recordset));  

        rstTitles->CursorType = adOpenDynamic;
        rstTitles->LockType = adLockPessimistic;

        // open Titles table
        TESTHR(rstTitles->Open("titles",
            _variant_t((IDispatch*)pConnection,true),
            adOpenDynamic, adLockPessimistic,adCmdTable));

        rstTitles->MoveFirst();
        pConnection->BeginTrans();

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

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

        // Loop through recordset and ask user if he wants
        // to change the type for a specified title.
        // Allocate memory to p_TempStr string pointer.
        p_TempStr = (LPSTR) malloc(sizeof(titlrs.m_szT_type));

        // Check for null string.
        assert(p_TempStr != NULL);
        while (VARIANT_FALSE == rstTitles->EndOfFile)
        {
            // Set the final character of the destination string to NULL.
            p_TempStr[sizeof(titlrs.m_szT_type)-1] = '\0';
            // The source string will get truncated if its length is 
            // longer than the length of the destination string minus one.
            strncpy(p_TempStr,strtok(titlrs.m_szT_type," "),sizeof(titlrs.m_szT_type)-1);
            
            // Compare type with psychology
            if (!strcmp(p_TempStr,"psychology")) 
            { 
                strTitle = titlrs.m_szT_title;
                strMessage = "Title: " + strTitle + 
                        "\n Change type to Self help?(y/n)";

                // Change the title for specified employee
                printf("%s\n",(LPCSTR)strMessage);
                do
                {
                    chKey = getch();
                }while(chKey != 'y' && chKey !='n');
                if(chKey == 'y')
                {
                    // Set the final character of the destination string to NULL.
                    titlrs.m_szT_type[sizeof(titlrs.m_szT_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(titlrs.m_szT_type,"self_help", sizeof(titlrs.m_szT_type)-1);
                    picRs->Update(&titlrs);
                }
            }
            rstTitles->MoveNext();
        }
        // Ask if the User wants to commit to all the 
        // changes made above
        printf("\n\n Save all changes(y/n)?");
        do
        {
            chKey = getch();
        }while(chKey != 'y' && chKey !='n');
    
        if(chKey == 'y')
            
            // Save the changes to the title table
            pConnection->CommitTrans();
        else
            // Unsave the changes to the title table
            pConnection->RollbackTrans();

        // Print current data in recordset.
        rstTitles->Requery(0);

        // Move to the first record of the title table
        rstTitles->MoveFirst();
        printf("\n\nPress any key to continue...");
        getch();

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

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

        // Rebind the Recordset to a C++ Class.
        TESTHR(picRs->BindToRecordset(&titlrs));

        while (!rstTitles->EndOfFile)
        {
            i= i+1;
            if (i % 23 == 0)
            {
                printf("\nPress any key to continue...");
                getch();

                //Clear the screen for the next display   
                //system("cls"); 
            }
            printf("%s -  %s\n",titlrs.m_szT_title,titlrs.m_szT_type);
            rstTitles->MoveNext();
        }
        // Restore original data becasue this is a demonstration.
        rstTitles->MoveFirst();

        while (VARIANT_FALSE == rstTitles->EndOfFile)
        {
            // Set the final character of the destination string to NULL.
            p_TempStr[sizeof(titlrs.m_szT_type)-1] = '\0';
            // The source string will get truncated if its length is 
            // longer than the length of the destination string minus one.
            strncpy(p_TempStr,titlrs.m_szT_type,sizeof(titlrs.m_szT_type)-1);
            p_TempStr = strtok(p_TempStr," ");

            if (!strcmp(p_TempStr,"self_help")) 
            {
                // Set the final character of the destination string to NULL.
                titlrs.m_szT_type[sizeof(titlrs.m_szT_type)-1] = '\0';
                // The source string will get truncated if its length is 
                // longer than the length of the destination string minus one.
                strncpy(titlrs.m_szT_type,"psychology",sizeof(titlrs.m_szT_type)-1);
                picRs->Update(&titlrs);           
            }
            rstTitles->MoveNext();  
        }
    }
    catch(_com_error &e)
    {
        // Notify the user of errors if any.
        _bstr_t bstrSource(e.Source());
        _bstr_t bstrDescription(e.Description());

        PrintProviderError(pConnection);

        printf("Source : %s\n",(LPCSTR)bstrSource);
        printf("Description : %s\n",(LPCSTR)bstrDescription);
    }

    // Deallocate the memory
    if (p_TempStr)
        free(p_TempStr);
    // Clean up objects before exit.
    //Release the IADORecordset Interface here   
    if (picRs)
        picRs->Release();
        
    if (rstTitles)
        if (rstTitles->State == adStateOpen)
            rstTitles->Close();
    if (pConnection)
        if (pConnection->State == adStateOpen)
            pConnection->Close();
};

///////////////////////////////////////////////////////////
//                                                       //
//      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;
    long      nCount  = 0;
    long      i       = 0;

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

BeginTransX.h

// BeginBeginTransH
#include "icrsint.h"

//This Class extracts only title and type 
class CTitlesRs : public CADORecordBinding
{
BEGIN_ADO_BINDING(CTitlesRs)
    //Column title is the 2nd field in the recordset  
    ADO_VARIABLE_LENGTH_ENTRY2(2, adVarChar, m_szT_title, 
         sizeof(m_szT_title), lT_titleStatus, FALSE)

    //Column type is the 3rd field in the recordset  
    ADO_VARIABLE_LENGTH_ENTRY2(3, adVarChar, m_szT_type, 
         sizeof(m_szT_type), lT_typeStatus, TRUE)
END_ADO_BINDING()

public:
   CHAR   m_szT_title[150];
   ULONG  lT_titleStatus;
   CHAR   m_szT_type[40];
   ULONG  lT_typeStatus;
};
// EndBeginTransH

See Also

BeginTrans, CommitTrans, and RollbackTrans Methods | Update Method