Ejemplo de métodos Execute, Requery y Clear (VC++)

En este ejemplo se muestra el método Execute cuando se ejecuta desde un objeto Command de y un objeto connection . También usa el método Requery para recuperar los datos actuales en un conjunto de registros de y el método Clear para borrar el contenido de la colección errors de . Las funciones ExecuteCommand y PrintOutput son necesarias para que se ejecute este ejemplo.

// Execute_Requery_Clear_Method_Sample.cpp  
// compile with: /EHsc  
#include <ole2.h>  
#include <stdio.h>  
  
#import "msado15.dll" no_namespace rename("EOF", "EndOfFile")  
  
// Function declarations  
inline void TESTHR(HRESULT x) { if FAILED(x) _com_issue_error(x); };  
void ExecuteX();  
void ExecuteCommand(_CommandPtr pCmdTemp, _RecordsetPtr pRstTemp);  
void PrintOutput(_RecordsetPtr pRstTemp);  
void PrintProviderError(_ConnectionPtr pConnection);  
void PrintComError(_com_error &e);  
  
int main() {  
   if ( FAILED(::CoInitialize(NULL)) )  
      return -1;  
  
   ExecuteX();  
   ::CoUninitialize();  
}  
  
void ExecuteX() {  
   // Define string variables.  
   _bstr_t strSQLChange("UPDATE Titles SET Type = 'self_help' WHERE Type = 'psychology'");  
   _bstr_t strSQLRestore("UPDATE Titles SET Type = 'psychology' WHERE Type = 'self_help'");  
   _bstr_t strCnn("Provider='sqloledb'; Data Source='My_Data_Source'; Initial Catalog='pubs'; Integrated Security='SSPI';");  
  
   // Define ADO object pointers.  Initialize pointers on define.  
   // These are in the ADODB::  namespace.  
   _ConnectionPtr pConnection = NULL;  
   _CommandPtr pCmdChange = NULL;  
   _RecordsetPtr pRstTitles = NULL;  
  
   try {  
      // Open connection.  
      TESTHR(pConnection.CreateInstance(__uuidof(Connection)));  
      pConnection->Open (strCnn, "", "", adConnectUnspecified);  
  
      // Create command object.  
      TESTHR(pCmdChange.CreateInstance(__uuidof(Command)));  
      pCmdChange->ActiveConnection = pConnection;  
      pCmdChange->CommandText = strSQLChange;  
  
      // Open titles table, casting Connection pointer to an   
      // IDispatch type so converted to correct type of variant.  
      TESTHR(pRstTitles.CreateInstance(__uuidof(Recordset)));  
      pRstTitles->Open ("Titles", _variant_t((IDispatch *) pConnection, true),   
         adOpenStatic, adLockOptimistic, adCmdTable);  
  
      // Print report of original data.  
      printf("\n\nData in Titles table before executing the query: \n");  
  
      // Call function to print loop recordset contents.  
      PrintOutput(pRstTitles);  
  
      // Clear extraneous errors from the Errors collection.  
      pConnection->Errors->Clear();  
  
      // Call ExecuteCommand subroutine to execute pCmdChange command.  
      ExecuteCommand(pCmdChange, pRstTitles);  
  
      // Print report of new data.  
      printf("\n\n\tData in Titles table after executing the query: \n");  
      PrintOutput(pRstTitles);  
  
      // Use Connection object's Execute method to execute SQL statement to restore data.  
      pConnection->Execute(strSQLRestore, NULL, adExecuteNoRecords);  
  
      // Retrieve the current data by requerying the recordset.  
      pRstTitles->Requery(adCmdUnknown);  
  
      // Print report of restored data.  
      printf("\n\n\tData after exec. query to restore original info: \n");  
      PrintOutput(pRstTitles);  
   }  
   catch (_com_error &e) {  
      PrintProviderError(pConnection);  
      PrintComError(e);  
   }  
  
   // Clean up objects before exit.  
   if (pRstTitles)  
      if (pRstTitles->State == adStateOpen)  
         pRstTitles->Close();  
   if (pConnection)  
      if (pConnection->State == adStateOpen)  
         pConnection->Close();  
}  
  
void ExecuteCommand(_CommandPtr pCmdTemp, _RecordsetPtr pRstTemp) {  
   try {  
      // CommandText property already set before function was called.  
      pCmdTemp->Execute(NULL, NULL, adCmdText);  
  
      // Retrieve the current data by requerying the recordset.  
      pRstTemp->Requery(adCmdUnknown);  
   }  
  
   catch(_com_error &e) {  
      // Notify user of any errors that result from executing the query.  
      // Pass a connection pointer accessed from the Recordset.  
      PrintProviderError(pRstTemp->GetActiveConnection());  
      PrintComError(e);  
   }  
}  
  
void PrintOutput(_RecordsetPtr pRstTemp) {  
   // Ensure at top of recordset.  
   pRstTemp->MoveFirst();  
  
   // If EOF is true, then no data and skip print loop.  
   if ( pRstTemp->EndOfFile )  
      printf("\tRecordset empty\n");  
   else {  
      // Define strings for output conversions.  Initialize to first record's values.  
      _bstr_t bstrTitle;  
      _bstr_t bstrType;  
  
      // Enumerate Recordset and print from each.  
      while ( !(pRstTemp->EndOfFile) ) {  
         // Convert variant string to convertible string type.  
         bstrTitle = pRstTemp->Fields->GetItem("Title")->Value;  
         bstrType  = pRstTemp->Fields->GetItem("Type")->Value;  
         printf("\t%s, %s \n", (LPCSTR) bstrTitle, (LPCSTR) bstrType);  
  
         pRstTemp->MoveNext();  
      }  
   }  
}  
  
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);  
}  

Consulte también

método Clear (ADO) de
del objeto Command (ADO) de
del objeto connection (ADO) de
colección de errores (ADO)
método Execute (comando ADO)
método Execute (conexión ADO)
método Requery de