Optimize, exemple de propriété (VC++)

Cet exemple illustre la propriété dynamique Optimize de l’objet Field. Le champ zip de la table Authors de la base de données Pubs n’est pas indexé. La définition de la propriété Optimize sur True dans le champ zip autorise ADO à créer un index qui améliore les performances de la méthode Find.

Exemple

// Optimize_Property_Sample.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 OptimizeX();  
void PrintProviderError(_ConnectionPtr pConnection);  
void PrintComError(_com_error &e);  
  
int main() {  
   if ( FAILED(::CoInitialize(NULL)) )  
      return -1;  
  
   OptimizeX();  
   ::CoUninitialize();  
}  
  
void OptimizeX() {  
   _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.  
   _RecordsetPtr pRst = NULL;  
  
   try {  
      TESTHR(pRst.CreateInstance(__uuidof(Recordset)));  
  
      // Enable Index creation.  
      pRst->CursorLocation = adUseClient;  
      pRst->Open ("SELECT * FROM authors", strCnn, adOpenStatic, adLockReadOnly, adCmdText);  
  
      // Create the index  
      pRst->Fields->GetItem("zip")->Properties->GetItem("Optimize")->PutValue("True");  
  
      // Find Akiko Yokomoto  
      pRst->Find("zip = '94595'", 1, adSearchForward);  
      printf("%s %s    %s %s %s",  
         (LPSTR) (_bstr_t) pRst->Fields->GetItem("au_fname")->Value,  
         (LPSTR) (_bstr_t) pRst->Fields->GetItem("au_lname")->Value,  
         (LPSTR) (_bstr_t) pRst->Fields->GetItem("address")->Value,  
         (LPSTR) (_bstr_t) pRst->Fields->GetItem("city")->Value,  
         (LPSTR) (_bstr_t) pRst->Fields->GetItem("state")->Value);  
  
      // Delete the index  
      pRst->Fields->GetItem("zip")->Properties->GetItem("Optimize")->PutValue("False");  
   }  
   catch (_com_error &e) {  
      // Display errors, if any.  Pass connection pointer accessed from the Recordset.  
      _variant_t vtConnect = pRst->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 occurred.");  
         break;  
      }  
   }  
  
   // Clean up objects before exit.  
   if (pRst)  
      if (pRst->State == adStateOpen)  
         pRst->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);  
}  

Akiko Yokomoto 3 Silver Ct. Walnut Creek CA

Voir aussi

Field, objet
Optimize, propriété dynamique (ADO)