Esempio della proprietà Item (VC++)

Questo esempio illustra il modo in cui la proprietà Item accede ai membri di una raccolta. Nell'esempio viene aperta la tabella Authors(Autori) del database Pubs (Pub) tramite un comando con parametri.

Il parametro nel comando eseguito sul database è accessibile dalla raccolta Parameters dell'oggetto Command in base all'indice e al nome. I campi del Recordset restituito sono quindi accessibili dalla raccoltaFields dell'oggetto in base all'indice e al nome.

// 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);  
}  

Vedere anche

Oggetto Command (ADO)
Raccolta Fields (ADO)
Proprietà Item (ADO)
Raccolta Parameters (ADO)
Oggetto Recordset (ADO)