Ejemplo de la propiedad de elemento (VC ++)

En este ejemplo se muestra cómo la propiedad Item accede a los miembros de una colección. En el ejemplo se abre la tabla Authors de la base de datos Pubs con un comando parametrizado.

Se accede al parámetro del comando emitido en la base de datos desde la colección Parameters del objeto Command por índice y nombre. Después, se obtiene acceso a los campos del objeto Recordset devuelto desde la colección Fields de dicho objeto por índice y nombre.

// BeginItemCpp.cpp  
// compile with: /EHsc  
#import "msado15.dll" no_namespace rename("EOF", "EndOfFile")  
  
#include <ole2.h>  
#include <stdio.h>  
#include <conio.h>  
  
// Function declarations  
inline void TESTHR(HRESULT x) {if FAILED(x) _com_issue_error(x);};  
void ItemX();  
void PrintProviderError(_ConnectionPtr pConnection);  
void PrintComError(_com_error &e);  
  
int main() {  
   if (FAILED(::CoInitialize(NULL)))  
      return -1;  
  
   ItemX();  
   ::CoUninitialize();  
}  
  
void ItemX() {  
   HRESULT hr = S_OK;  
  
   // Define ADO object pointers.  Initialize pointers on define.  These are in the ADODB::  namespace.  
   _ConnectionPtr pConnection = NULL;  
   _RecordsetPtr pRst = NULL;  
   _CommandPtr pCmd = NULL;  
   _ParameterPtr pPrm = NULL;  
   FieldPtr pFld = NULL;  
  
   // Other Variables.  
   _bstr_t strCnn("Provider='sqloledb'; Data Source='My_Data_Source'; Initial Catalog='pubs'; Integrated Security='SSPI';");  
   _variant_t Column[9];  
   _variant_t vIndex;  
  
   try {  
      // Open connection.  
      TESTHR(pConnection.CreateInstance(__uuidof(Connection)));  
      TESTHR(pRst.CreateInstance(__uuidof(Recordset)));  
      TESTHR(pCmd.CreateInstance(__uuidof(Command)));  
  
      // Set the array with the authors table field (column) names  
      Column[0] = "au_id";  
      Column[1] = "au_lname";  
      Column[2] = "au_fname";  
      Column[3] = "phone";  
      Column[4] = "address";  
      Column[5] = "city";  
      Column[6] = "state";  
      Column[7] = "zip";  
      Column[8] = "contract";  
  
      _bstr_t strText("SELECT * FROM authors WHERE state = ?");  
      pCmd->CommandText = strText;  
  
      pPrm = pCmd->CreateParameter("ItemXparm", adChar, adParamInput, 2, "CA");  
      pCmd->Parameters->Append(pPrm);  
  
      pConnection->Open(strCnn, "", "", adConnectUnspecified);  
      pCmd->ActiveConnection = pConnection;  
  
      // Connection and CommandType are omitted because a Command object is provided.  
      _variant_t Conn;  
      Conn.vt = VT_ERROR;  
      Conn.scode = DISP_E_PARAMNOTFOUND;  
  
      pRst->Open((_variant_t((IDispatch *) pCmd)), Conn, adOpenStatic, adLockReadOnly, -1);  
  
      printf("The Parameters collection accessed by index...\n");  
  
      vIndex = (short) 0;  
      pPrm = pCmd->Parameters->GetItem(&vIndex);  
      printf("Parameter name = '%s', value = '%s'\n",  
         (LPCSTR)pPrm->Name, (LPSTR)(_bstr_t)pPrm->Value);  
  
      printf("\nThe Parameters collection accessed by name...\n");  
      pPrm = pCmd->Parameters->Item["ItemXparm"];  
      printf("Parameter name = '%s', value = '%s'\n",  
         (LPCSTR)pPrm->Name, (LPSTR)(_bstr_t)pPrm->Value);  
  
      printf("\nThe Fields collection accessed by index...\n");  
      pRst->MoveFirst();  
      long limit = 0;  
      limit = ((pRst->Fields->Count) - 1);  
      int intLineCnt = 8;   
      for (short iIndex = 0 ; iIndex <= limit ; iIndex++) {  
         vIndex = iIndex;  
  
         pFld = pRst->Fields->GetItem(&vIndex);  
         printf("Field %d : Name =  '%s', ", iIndex, (LPCSTR)pFld->GetName());  
         _variant_t FldVal = pFld->GetValue();    
  
         // Because Value is the default property of a Property object, the use   
         // of the actual keyword here is optional.  
         switch(FldVal.vt) {  
         case (VT_BOOL):  
            if (FldVal.boolVal)  
               printf("Value = 'True'");  
            else  
               printf("Value = 'False'");  
            printf("\n");  
            break;  
         case (VT_BSTR):  
            printf("Value = '%s'",  
               (LPCSTR)(_bstr_t)FldVal.bstrVal);  
            printf("\n");  
            break;  
         case (VT_I4):  
            printf("Value = '%s'",(LPCSTR)FldVal.iVal);  
            printf("\n");  
            break;  
         case (VT_EMPTY):  
            printf("Value = '%s'",(LPCSTR)FldVal.lVal);  
            printf("\n");  
            break;  
         default:  
            break;  
         }  
      }  
  
      printf("\nThe Fields collection accessed by name...\n");  
      pRst->MoveFirst();  
  
      for (int iIndex = 0; iIndex <= 8 ; iIndex++) {  
         intLineCnt++;  
  
         pFld = pRst->Fields->GetItem(Column[iIndex]);  
         printf("Field name = '%s', ", (LPCSTR)pFld->GetName());  
         _variant_t FldVal = pFld->GetValue();  
  
         // Because Value is the default property of a Property object,  
         // the use of the actual keyword here is optional.  
         switch(FldVal.vt) {  
         case (VT_BOOL):  
            if (FldVal.boolVal)  
               printf("Value = 'True'");  
            else  
               printf("Value = 'False'");  
            printf("\n");  
            break;  
         case (VT_BSTR):  
            printf("Value = '%s'",  
               (LPCSTR)(_bstr_t)FldVal.bstrVal);  
            printf("\n");  
            break;  
         case (VT_I4):  
            printf("Value = '%s'", (LPCSTR)FldVal.iVal);  
            printf("\n");  
            break;  
         case (VT_EMPTY):  
            printf("Value = '%s'", (LPCSTR)FldVal.lVal);  
            printf("\n");  
            break;  
         default:  
            break;  
         }  
      }  
   }  
   catch(_com_error &e) {  
      // Notify the user of errors if any.  
      // Pass a connection pointer accessed from the Recordset.  
      PrintProviderError(pConnection);  
      PrintComError(e);  
   }  
  
   // Clean up objects before exit.  
   if (pRst)  
      if (pRst->State == adStateOpen)  
         pRst->Close();  
   if (pConnection)  
      if (pConnection->State == adStateOpen)  
         pConnection->Close();  
}  
  
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

Objeto Command (ADO)
Fields (colección) (ADO)
Propiedad Item (ADO)
Colección de parámetros (ADO)
Objeto de conjunto de registros (ADO)