Esempio della proprietà MaxRecords (VC++)

In questo esempio viene usata la proprietà MaxRecords per aprire un Recordset contenente i 10 titoli più costosi nella tabella Titles.

Esempio

// MaxRecords_Property_Example.cpp  
// compile with: /EHsc  
#import "msado15.dll" no_namespace rename("EOF","EndOfFile")  
  
#include <ole2.h>  
#include <stdio.h>  
#include <conio.h>  
#include "icrsint.h"  
  
// This class extracts titles and type from the titles table  
class CTitleRs : public CADORecordBinding {  
   BEGIN_ADO_BINDING(CTitleRs)  
  
      // Column title is the 1st field in the Recordset  
      ADO_VARIABLE_LENGTH_ENTRY2(1, adVarChar,m_szau_Title,  
      sizeof(m_szau_Title), lau_TitleStatus, FALSE)  
  
      // Column price is the 2nd field in the Recordset  
      ADO_VARIABLE_LENGTH_ENTRY2(2, adDouble, m_szau_Price,  
      sizeof(m_szau_Price), lau_PriceStatus, FALSE)  
  
   END_ADO_BINDING()  
  
public:  
   CHAR m_szau_Title[81];  
   ULONG lau_TitleStatus;  
   DOUBLE m_szau_Price;  
   ULONG lau_PriceStatus;  
};  
  
// Function Declarations  
inline void TESTHR(HRESULT x) { if FAILED(x) _com_issue_error(x); };  
void MaxRecordsX();  
void PrintProviderError(_ConnectionPtr pConnection);  
void PrintComError(_com_error &e);  
  
int main() {  
   if ( FAILED(::CoInitialize(NULL)) )  
      return -1;  
  
   MaxRecordsX();  
   ::CoUninitialize();  
}  
  
void  MaxRecordsX() {  
   // Define ADO ObjectPointers.  Initialize Pointers on define  
   // These are in the ADODB :: namespace  
   _RecordsetPtr pRstTemp = NULL;  
  
   // Define Other Variables  
   IADORecordBinding *picRs = NULL;   // Interface Pointer Declared    
   CTitleRs titlers;   // C++ Class Object  
  
   try {  
      // Assign Connection String to Variable  
      _bstr_t strCnn("Provider='sqloledb'; Data Source='My_Data_Source'; Initial Catalog='pubs'; Integrated Security='SSPI';");  
  
      // Open Recordset containing the 10 most expensive titles in the Titles table.  
      TESTHR(pRstTemp.CreateInstance(__uuidof(Recordset)));  
  
      pRstTemp->MaxRecords = 10;  
  
      pRstTemp->Open("SELECT title,price FROM Titles ORDER BY Price DESC",  
         strCnn, adOpenForwardOnly, adLockReadOnly, adCmdText);  
  
      // Open IADORecordBinding interface pointer for binding Recordset to a class  
      TESTHR(pRstTemp->QueryInterface(__uuidof(IADORecordBinding), (LPVOID*)&picRs));  
  
      // Bind the Recordset to a C++ class here  
      TESTHR(picRs->BindToRecordset(&titlers));  
  
      // Display the contents of the Recordset  
      printf("Top Ten Titles by Price:\n\n");  
  
      while ( !(pRstTemp->EndOfFile) ) {  
         printf("%s ---  %6.2lf\n", titlers.lau_TitleStatus == adFldOK ?   
            titlers.m_szau_Title : "<NULL>", titlers.lau_PriceStatus == adFldOK ?   
            titlers.m_szau_Price : 0.00);  
         pRstTemp->MoveNext();  
      }  
   }  
   catch(_com_error &e) {  
      // Display errors, if any.  Pass connection pointer accessed from the Recordset.  
      _variant_t vtConnect = pRstTemp->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. Release the IADORecordset Interface here     
   if (picRs)  
      picRs->Release();  
  
   if (pRstTemp)  
      if (pRstTemp->State == adStateOpen)  
         pRstTemp->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);  
}  

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Vedere anche

Proprietà MaxRecords (ADO)
Oggetto Recordset (ADO)