Пример свойств Filter и RecordCount (Visual c++)Filter and RecordCount Properties Example (VC++)

В этом примере используется свойство Filter для открытия нового набора записей на основе указанного условия, примененного к существующему набору записей.This example uses the Filter property to open a new Recordset based on a specified condition applied to an existing Recordset. Для отображения числа записей в двух наборах записейиспользуется свойство RecordCount .It uses the RecordCount property to show the number of records in the two Recordsets. Для выполнения этой процедуры требуется функция Филтерфиелд.The FilterField function is required for this procedure to run.

ПримерExample

// BeginFilterCpp.cpp  
// compile with: /EHsc /c  
#import "msado15.dll" no_namespace rename("EOF", "EndOfFile")  
  
#include <stdio.h>  
#include <ole2.h>  
#include <conio.h>  
#include "icrsint.h"  
  
// Class extracts only Pub Name and Country Name.  
class CPublishers : public CADORecordBinding {  
   BEGIN_ADO_BINDING(CPublishers)  
  
   // Column Pub Name is the 2nd field in the recordset  
   ADO_VARIABLE_LENGTH_ENTRY2(2, adVarChar, m_szP_pubname, sizeof(m_szP_pubname),   
                              lP_pubnameStatus, TRUE)  
  
   // Column Country Name is the 5th field in the recordset  
   ADO_VARIABLE_LENGTH_ENTRY2(5, adVarChar, m_szP_country, sizeof(m_szP_country),   
                              lP_countryStatus, TRUE)  
  
   END_ADO_BINDING()  
  
public:  
   CHAR m_szP_pubname[50];  
   ULONG lP_pubnameStatus;  
   CHAR m_szP_country[50];  
   ULONG lP_countryStatus;  
};  
  
// Function declarations  
inline void TESTHR(HRESULT x) { if FAILED(x) _com_issue_error(x); };  
void FilterX();  
_RecordsetPtr FilterField(_RecordsetPtr rstTemp, _bstr_t strField, _bstr_t strFilter);  
void FilterX2();  
void PrintProviderError(_ConnectionPtr pCnn1);  
void PrintComError(_com_error &e);  
  
inline char* mygets(char* strDest, int n) {  
   char strExBuff[10];  
   char* pstrRet = fgets(strDest, n, stdin);  
  
   if (pstrRet == NULL)  
      return NULL;  
  
   if (!strrchr(strDest, '\n'))  
      // Exhaust the input buffer.  
      do {  
         fgets(strExBuff, sizeof(strExBuff), stdin);  
      } while (!strrchr(strExBuff, '\n'));  
   else  
      // Replace '\n' with '\0'  
      strDest[strrchr(strDest, '\n') - strDest] = '\0';  
  
   return pstrRet;  
}  
  
int main() {  
   HRESULT hr = S_OK;  
  
   if ( FAILED(::CoInitialize(NULL)) )  
      return -1;  
  
   FilterX();  
   FilterX2();  
  
   ::CoUninitialize();  
}  
  
void FilterX() {  
   // Define ADO object pointers, initialize pointers on define.  These are in the ADODB::  namespace.  
   _RecordsetPtr rstPublishers = NULL;  
   _RecordsetPtr rstPublishersCountry = NULL;  
  
   // Define Other Variables  
   HRESULT hr = S_OK;  
   _bstr_t strCnn("Provider='sqloledb'; Data Source='My_Data_Source'; Initial Catalog='pubs'; Integrated Security='SSPI';");  
   int intPublisherCount = 0;  
   long recCount = 0;  
   _bstr_t strCountry;   
   _bstr_t strMessage;  
   char *tempStr;  
   CHAR sz_CountryName[50];  
   bool boolFlag = TRUE;  
   char * token1;  
  
   try {  
      // Open recordset with data from Publishers table.  
      rstPublishers.CreateInstance(__uuidof(Recordset));  
      rstPublishersCountry.CreateInstance(__uuidof(Recordset));  
  
      rstPublishers->CursorType = adOpenStatic;  
  
      TESTHR(rstPublishers->Open("publishers", strCnn, adOpenStatic , adLockReadOnly, adCmdTable));  
  
      // Populate the Recordset.  
      intPublisherCount = rstPublishers->RecordCount;  
  
      // Get user input.  
      printf("Enter a country to filter on:");  
      mygets(sz_CountryName, 50);  
  
      // Trim the string  
      tempStr = strtok_s(sz_CountryName, "  \t", &token1);  
      strCountry = tempStr;  
      if (tempStr == NULL)  
         boolFlag = FALSE;  
  
      if (boolFlag) {  
         if (strcmp(sz_CountryName,"")) {  
            // Open a filtered Recordset object.  
            rstPublishersCountry = FilterField(rstPublishers, "Country", strCountry);  
            recCount = rstPublishersCountry->GetRecordCount();  
            if (recCount == 0)  
               printf("\nNo publishers from that country.\n");  
            else {  
               // Print number of records for the original recordset object and the   
               // filtered Recordset object.  
               printf("\nOrders in original recordset:\n%d", intPublisherCount);  
               printf("\nOrders in filtered recordset (Country = '%s'): \n%d\n\n",   
                      (LPCSTR)strCountry, rstPublishersCountry->RecordCount);  
            }  
         }  
      }  
   }  
   catch(_com_error &e) {  
      // Notify the user of errors if any.  
      _variant_t vtConnect = rstPublishers->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;  
      }  
   }  
  
   // Clean up objects before exit.  
   if (rstPublishers)  
      if (rstPublishers->State == adStateOpen)  
         rstPublishers->Close();  
   if (rstPublishersCountry)  
      if (rstPublishersCountry->State == adStateOpen)  
         rstPublishersCountry->Close();  
}  
  
_RecordsetPtr FilterField(_RecordsetPtr rstTemp,_bstr_t strField, _bstr_t strFilter) {  
   // Set a filter on the specified Recordset object and then open a new Recordset object.  
   rstTemp->Filter  = strField + " = '" + strFilter + "'";  
   return rstTemp;  
}  
  
void FilterX2() {  
   _RecordsetPtr rstPublishers;  
   CPublishers publishers;  
  
   // Define Other Variables  
   HRESULT hr = S_OK;  
   IADORecordBinding *picRs = NULL;   // Interface Pointer declared  
  
   _bstr_t strCnn("Provider='sqloledb'; Data Source='My_Data_Source'; Initial Catalog='pubs'; Integrated Security='SSPI';");  
   try {  
      // Open recordset with data from Publishers table.  
      rstPublishers.CreateInstance(__uuidof(Recordset));   
      rstPublishers->CursorType = adOpenStatic;  
  
      TESTHR(rstPublishers->Open("SELECT * FROM publishers WHERE "  
         "Country='USA'", strCnn, adOpenStatic, adLockReadOnly, adCmdText));  
  
      // Open an IADORecordBinding interface pointer   
      // which we'll use for Binding Recordset to a class  
      TESTHR(rstPublishers->QueryInterface(__uuidof(IADORecordBinding), (LPVOID*)&picRs));  
  
      // Bind the Recordset to a C++ Class here   
      TESTHR(picRs->BindToRecordset(&publishers));  
  
      // Print current data in recordset.  
      rstPublishers->MoveFirst();  
  
      while (!rstPublishers->EndOfFile) {  
         printf("%s, %s\n",   
            publishers.lP_pubnameStatus == adFldOK ?   
            publishers.m_szP_pubname: "<NULL>",  
            publishers.lP_countryStatus == adFldOK ?   
            publishers.m_szP_country: "<NULL>");  
  
         rstPublishers->MoveNext();  
      }  
   }  
   catch (_com_error &e) {  
      // Notify the user of errors if any.  
      _variant_t vtConnect = rstPublishers->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;  
      }  
   }  
  
   // Clean up objects before exit.  Release the IADORecordset Interface here     
   if (picRs)  
      picRs->Release();  
  
   if (rstPublishers)  
      if (rstPublishers->State == adStateOpen)  
         rstPublishers->Close();  
}  
  
void PrintProviderError(_ConnectionPtr pCnn1) {  
   // Print Provider Errors from Connection object.  
   // pErr is a record object in the Connection's Error collection.  
   ErrorPtr pErr  = NULL;  
  
   if ( (pCnn1->Errors->Count) > 0) {  
      long nCount = pCnn1->Errors->Count;  
      // Collection ranges from 0 to nCount -1.  
      for (long i = 0 ; i < nCount ; i++) {  
         pErr = pCnn1->Errors->GetItem(i);  
         printf("\t Error number: %x\t%s", pErr->Number, (LPCSTR) 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);  
}  

Пример вводаSample Input

USA  

Пример выходных данныхSample Output

Orders in original recordset:  
8  
Orders in filtered recordset (Country = 'USA'):  
6  
  
New Moon Books, USA  
Binnet & Hardley, USA  
Algodata Infosystems, USA  
Five Lakes Publishing, USA  
Ramona Publishers, USA  
Scootney Books, USA  

См. такжеSee Also

Свойство Filter Filter Property
Свойство RecordCount (ADO) RecordCount Property (ADO)
Объект Recordset (ADO)Recordset Object (ADO)