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.
#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();
::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=srv;"
"Initial Catalog=Pubs;User Id=sa;Password=;");
TESTHR(pConnection.CreateInstance(__uuidof(Connection)));
TESTHR(pConnection->Open(strCnn,"","",NULL));
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)
{
// Remove blank string
strcpy(p_TempStr,strtok(titlrs.m_szT_type," "));
// 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')
{
// Copy "self_help" title field
strcpy(titlrs.m_szT_type,"self_help");
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 because this is a demonstration.
rstTitles->MoveFirst();
while (VARIANT_FALSE == rstTitles->EndOfFile)
{
strcpy(p_TempStr,titlrs.m_szT_type);
p_TempStr = strtok(p_TempStr," ");
if (!strcmp(p_TempStr,"self_help"))
{
strcpy(titlrs.m_szT_type,"psychology");
picRs->Update(&titlrs);
}
rstTitles->MoveNext();
}
// Deallocate the memory
free(p_TempStr);
// Clean up objects before exit.
rstTitles->Close();
pConnection->Close();
//Release IADORecordset Interface
if (picRs)
picRs->Release();
}
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);
}
};
///////////////////////////////////////////////////////////
// //
// 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);
}
}
}
BeginTransX.h:
#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;
};