MDAC 2.5 SDK - ADO

MaxRecords Property Example (VC++)

See Also

This example uses the MaxRecords property to open a Recordset containing the 10 most expensive titles in the Titles table.

#import "C:\Program Files\Common Files\System\ADO\msado15.dll"\
    no_namespace rename("EOF","EndOfFile")

#include <ole2.h>
#include <stdio.h>
#include <conio.h>
#include "MaxRecordsX.h"

// Function Declarations
inline void TESTHR(HRESULT x) {if FAILED(x) _com_issue_error(x);};
void MaxRecordsX(void);
void PrintProviderError(_ConnectionPtr pConnection);
void PrintComError(_com_error &e);

//////////////////////////////////////////////////////////////
//                                                          //
//                        Main Function                     //
//                                                          //
//////////////////////////////////////////////////////////////

void main()
{
    if(FAILED(::CoInitialize(NULL)))
        return;

    MaxRecordsX();

    ::CoUninitialize();
}

//   MaxRecordsX()  Function
void  MaxRecordsX(void)
{
    // 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  
    CTitlesRs titlers;            // C++ Class Object
    HRESULT hr = S_OK;

    try
    {
        //Assign Connection String to Variable
        _bstr_t strCnn("Provider=sqloledb;Data Source=srv;"
                    "Initial Catalog=Pubs;User Id=sa;Password=;");
        
        // 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 an IADORecordBinding interface pointer which 
        // we will use 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\n",titlers.lau_TitleStatus == 
                adFldOK ? titlers.m_szau_Title : "<NULL>",
                    titlers.lau_PriceStatus == adFldOK ? 
                    titlers.m_szau_Price : 0.00);
            pRstTemp->MoveNext();
        }
        // Clean up objects before exit.
        pRstTemp->Close();
        if(picRs)
            picRs->Release();
    }
    catch(_com_error &e)
    {
       // Notify the user of errors if any.
       // Pass a 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 occured.");
                break;
        }
    }
};

//////////////////////////////////////////////////////////////
//                                                          //
//                  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,
                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);
}

MaxRecordsX.h:

// MaxRecordsX.h

#include "icrsint.h"

// This class extracts titles and type from the Titles table

class CTitlesRs : public CADORecordBinding
{
    BEGIN_ADO_BINDING(CTitlesRs)
        // 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;
};