Ejemplo del método GetRows (VC++)

Se aplica a: Access 2013, Office 2013

En este ejemplo se usa el método GetRows para recuperar un número especificado de filas de un objeto Recordset y rellenar una matriz con los datos resultantes. El método GetRows devolverá un número de filas menor que el deseado en los dos siguientes casos: si se alcanza EOF o si GetRows ha tratado de recuperar un registro anteriormente eliminado por otro usuario. La función devuelve False sólo si se produce el segundo caso. Se requiere la función GetRowsOK para que se ejecute este procedimiento.

 
// BeginGetRowsCpp 
#import "C:\Program Files\Common Files\System\ADO\msado15.dll" no_namespace rename("EOF", "EndOfFile") 
 
#include <stdio.h> 
#include <ole2.h> 
#include <conio.h> 
 
// Function Declarations 
inline void TESTHR(HRESULT x) {if FAILED(x) _com_issue_error(x);}; 
void GetRowsX(void); 
bool GetRowsOK(_RecordsetPtr pRstTemp,int intNumber, 
 _variant_t& avarData); 
void PrintProviderError(_ConnectionPtr pConnection); 
void PrintComError(_com_error &e); 
 
void main() 
{ 
 if(FAILED(::CoInitialize(NULL))) 
 return; 
 
 GetRowsX(); 
 
 ::CoUninitialize(); 
} 
 
/////////////////////////////////////////////////////////// 
// // 
// GetRowsX Function // 
// // 
/////////////////////////////////////////////////////////// 
 
void GetRowsX(void) 
{ 
 HRESULT hr = S_OK; 
 
 // Define string variables. 
 _bstr_t strCnn("Provider='sqloledb';Data Source='MySqlServer';" 
 "Initial Catalog='pubs';Integrated Security='SSPI';"); 
 
 // Define ADO object pointers. 
 // Initialize pointers on define. 
 // These are in the ADODB:: namespace. 
 _RecordsetPtr pRstEmployees = NULL; 
 
 try 
 { 
 // Open recordset with names and hire dates from employee table. 
 TESTHR(pRstEmployees.CreateInstance(__uuidof(Recordset))); 
 
 pRstEmployees->Open("SELECT fName, lName, hire_date " 
 "FROM Employee ORDER BY lName",strCnn, 
 adOpenStatic, adLockReadOnly,adCmdText); 
 
 
 while (true) //continuous loop 
 { 
 int intLines = 0; 
 
 // Get user input for number of rows. 
 printf("\nEnter number of rows to retrieve (0 to exit): "); 
 int intRows; 
 scanf("%d", &intRows); 
 
 if (intRows <= 0) 
 break; 
 
 //Clear the screen for the next display 
 system("cls"); 
 
 
 // If GetRowsOK is successful, print the results, 
 // noting if the end of the file was reached. 
 _variant_t avarRecords; 
 
 if (GetRowsOK(pRstEmployees, intRows, avarRecords)) 
 { 
 long lUbound; 
 HRESULT hr = SafeArrayGetUBound(avarRecords.parray, 
 2,&lUbound); 
 
 if (hr == 0) 
 { 
 if (intRows > lUbound + 1) 
 { 
 printf("\n(Not enough records in Recordset to " 
 "retrieve %d rows)\n", intRows); 
 } 
 } 
 printf("%d records found.", lUbound+1); 
 
 // Print the retrieved data. 
 for (int intRecords = 0;intRecords < lUbound+1; 
 intRecords++) 
 { 
 printf("\n "); 
 
 long rgIndices[2]; 
 rgIndices[0] = 0; 
 rgIndices[1] = intRecords; 
 _variant_t result; 
 result.vt = VT_BSTR; 
 
 hr= SafeArrayGetElement(avarRecords.parray, 
 rgIndices, &result); 
 
 if (hr == 0){printf("%s ",(LPCSTR)(_bstr_t)result);} 
 
 rgIndices[0] = 1; 
 
 hr= SafeArrayGetElement(avarRecords.parray, 
 rgIndices, &result); 
 
 if (hr == 0){printf("%s, ",(LPCSTR)(_bstr_t)result);} 
 
 rgIndices[0] = 2; 
 
 hr= SafeArrayGetElement(avarRecords.parray, 
 rgIndices, &result); 
 
 if (hr == 0){printf("%s",(LPCSTR)(_bstr_t)result);} 
 
 intLines ++; 
 
 if (intLines % 10 == 0) 
 { 
 printf("\nPress any key to continue..."); 
 getch(); 
 
 intLines = 0; 
 
 //Clear the screen for the next display 
 system("cls"); 
 } 
 } 
 } 
 else 
 { 
 // Assuming the GetRows error was due to data 
 // changes by another user, use Requery to 
 // refresh the Recordset and start over. 
 printf("GetRows failed--retry?\n"); 
 char chKey; 
 do 
 { 
 chKey = getch(); 
 }while(toupper(chKey) != 'Y' && toupper(chKey) != 'N'); 
 
 if(toupper(chKey) == 'Y') 
 { 
 pRstEmployees->Requery(adOptionUnspecified); 
 } 
 else 
 { 
 printf("GetRows failed!\n"); 
 break; 
 } 
 } 
 
 // Because using GetRows leaves the current 
 // record pointer at the last record accessed, 
 // move the pointer back to the beginning of the 
 // Recordset before looping back for another search. 
 pRstEmployees->MoveFirst(); 
 } 
 } 
 catch(_com_error &e) 
 { 
 // Notify the user of errors if any. 
 // Pass a connection pointer accessed from the Recordset. 
 _variant_t vtConnect = pRstEmployees->GetActiveConnection(); 
 
 // GetActiveConnection returns connect string if connection 
 // is not open, else returns Connection object. 
 switch(vtConnect.vt) 
 { 
 case VT_BSTR: 
 PrintComError(e); 
 break; 
 case VT_DISPATCH: 
 PrintProviderError(vtConnect); 
 break; 
 default: 
 printf("Errors occured."); 
 break; 
 } 
 } 
 
 //Clean up objects before exit. 
 if (pRstEmployees) 
 if (pRstEmployees->State == adStateOpen) 
 pRstEmployees->Close(); 
} 
 
bool GetRowsOK(_RecordsetPtr pRstTemp,int intNumber, 
 _variant_t& avarData) 
{ 
 // Store results of GetRows method in array. 
 avarData = pRstTemp->GetRows(intNumber); 
 
 // Return False only if fewer than the desired 
 // number of rows were returned, but not because the 
 // end of the Recordset was reached. 
 long lUbound; 
 HRESULT hr = SafeArrayGetUBound(avarData.parray,2,&lUbound); 
 if (hr == 0) 
 { 
 if ((intNumber > lUbound + 1) && (!(pRstTemp->EndOfFile))) 
 return false; 
 else 
 return true; 
 } 
 else 
 { 
 printf ("\nUnable to Get the Array's Upper Bound\n"); 
 return false; 
 } 
} 
 
/////////////////////////////////////////////////////////// 
// // 
// 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; 
 
 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); 
 } 
 } 
} 
 
/////////////////////////////////////////////////////////// 
// // 
// PrintComError Function // 
// // 
/////////////////////////////////////////////////////////// 
 
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); 
} 
// EndGetRowsCpp