Ejemplo de los métodos BeginTrans, CommitTrans y RollbackTrans (VC++)

Se aplica a: Access 2013, Office 2013

En este ejemplo se cambia el tipo de libro de todos los libros de psicología de la tabla Titles de la base de datos. Una vez que el método BeginTrans inicia una transacción que aísla todos los cambios realizados en la tabla Titles , el método CommitTrans guarda los cambios. Puede utilizar el método RollbackTrans para deshacer los cambios guardados mediante el método Update.

 
// 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