Ejemplo del método Seek y de la propiedad Index (VC++)

Se aplica a: Access 2013, Office 2013

En este ejemplo se usa el método Seek del objeto Recordset y la propiedad Index junto con un identificador de empleado determinado para buscar el nombre del empleado en la tabla Employees de la base de datos Nwind.mdb.

 
// BeginSeekCpp 
#import "C:\Program Files\Common Files\System\ADO\msado15.dll" no_namespace rename("EOF", "EndOfFile") 
 
#include <stdio.h> 
#include <ole2.h> 
#include <conio.h> 
#include <string.h> 
#include "SeekX.h" 
 
//Function declarations 
inline void TESTHR(HRESULT x) {if FAILED(x) _com_issue_error(x);}; 
void SeekX(void); 
void PrintProviderError(_ConnectionPtr pConnection); 
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; 
} 
 
////////////////////////////////////////////////////////// 
// // 
// Main Function // 
// // 
////////////////////////////////////////////////////////// 
void main() 
{ 
 if(FAILED(::CoInitialize(NULL))) 
 return; 
 
 SeekX(); 
 
 ::CoUninitialize(); 
} 
 
////////////////////////////////////////////////////////// 
// // 
// SeekX Function // 
// // 
////////////////////////////////////////////////////////// 
void SeekX() 
{ 
 HRESULT hr = S_OK; 
 
 // Define ADO object pointers. 
 // Initialize pointers on define. 
 // These are in the ADODB:: namespace. 
 
 _RecordsetPtr pRstEmp = NULL; 
 
 IADORecordBinding *picRs = NULL; // Interface Pointer declared 
 CEmployeeRs EmpRs; //C++ class object 
 
 //Definitions of other variables 
 _bstr_t strPrompt("Enter an EmployeeID (e.g., 1 to 9)"); 
 char strEmpId[2]; 
 
 try 
 { 
 TESTHR(pRstEmp.CreateInstance(__uuidof(Recordset))); 
 pRstEmp->CursorLocation = adUseServer; 
 pRstEmp->Open("employees", "Provider='Microsoft.Jet.OLEDB.4.0';" 
 "Data Source='C:\\Program Files\\Microsoft Office\\Office\\" 
 "Samples\\Northwind.mdb';", 
 adOpenKeyset,adLockReadOnly,adCmdTableDirect); 
 
 //Open an IADORecordBinding interface pointer which 
 //we'll use for binding Recordset to a Class 
 TESTHR(pRstEmp->QueryInterface( 
 __uuidof(IADORecordBinding), (LPVOID*)&picRs)); 
 
 //Bind the Recordset to a C++ Class 
 TESTHR(picRs->BindToRecordset(&EmpRs)); 
 
 //Does this provider support Seek and Index? 
 if (pRstEmp->Supports(adIndex) && pRstEmp->Supports(adSeek)) 
 { 
 pRstEmp->Index = "PrimaryKey"; 
 
 //Display all the employees. 
 pRstEmp->MoveFirst(); 
 while (!pRstEmp->EndOfFile) 
 { 
 printf("%d : %s %s\n", 
 EmpRs.le_empidStatus == adFldOK ? 
 EmpRs.m_ie_empid : 0, 
 EmpRs.le_fnameStatus == adFldOK ? 
 EmpRs.m_sze_fname : "<NULL>", 
 EmpRs.le_lnameStatus == adFldOK ? 
 EmpRs.m_sze_lname : "<NULL>"); 
 
 pRstEmp->MoveNext(); 
 } 
 //Prompt the user for an EmployeeID between 1 and 9. 
 do 
 { 
 pRstEmp->MoveFirst(); 
 printf("\n\n%s\t",(LPCSTR) strPrompt); 
 mygets(strEmpId, 2); 
 
 //Quit if strEmpID is a zero-length string 
 //(CANCEL, null, etc.) 
 char *strTemp = strtok(strEmpId," \t"); 
 if (strTemp == NULL) break; 
 if (strlen(strTemp) == 1 && atoi(strTemp) >= 1 && 
 atoi(strTemp) <= 9) 
 { 
 _variant_t strEmployeeId(strTemp); 
 pRstEmp->Seek(strEmployeeId, adSeekAfterEQ); 
 if (pRstEmp->EndOfFile) 
 { 
 printf("Employee not found.\n"); 
 } 
 else 
 { 
 printf("%d : Employee='%s %s'\n", 
 EmpRs.le_empidStatus == adFldOK ? 
 EmpRs.m_ie_empid : 0, 
 EmpRs.le_fnameStatus == adFldOK ? 
 EmpRs.m_sze_fname : "<NULL>", 
 EmpRs.le_lnameStatus == adFldOK ? 
 EmpRs.m_sze_lname : "<NULL>"); 
 } 
 } 
 } 
 while(true); 
 } 
 } 
 catch(_com_error &e) 
 { 
 // Notify the user of errors if any. 
 // Pass a connection pointer accessed from the Recordset. 
 _variant_t vtConnect = pRstEmp->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 (pRstEmp) 
 if (pRstEmp->State == adStateOpen) 
 pRstEmp->Close(); 
} 
 
/////////////////////////////////////////////////////////// 
// // 
// 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); 
} 
// EndSeekCpp 

SeekX.h

 
// BeginSeekH 
#include "icrsint.h" 
 
// This Class extracts only EmployeeId,FirstName and LastName 
// from employees table 
class CEmployeeRs : public CADORecordBinding 
{ 
BEGIN_ADO_BINDING(CEmployeeRs) 
 
 // Column hiredate is the 1st field in the table. 
 ADO_VARIABLE_LENGTH_ENTRY2(1, adInteger,m_ie_empid, 
 sizeof(m_ie_empid), le_empidStatus, FALSE) 
 
 // Column LastName is the 2nd field in the table. 
 ADO_VARIABLE_LENGTH_ENTRY2(2, adVarChar, m_sze_lname, 
 sizeof(m_sze_lname), le_lnameStatus, FALSE) 
 
 // Column FirstName is the 3rd field in the table. 
 ADO_VARIABLE_LENGTH_ENTRY2(2, adVarChar, m_sze_fname, 
 sizeof(m_sze_fname), le_fnameStatus, FALSE) 
END_ADO_BINDING() 
 
public: 
 INT m_ie_empid; 
 ULONG le_empidStatus; 
 CHAR m_sze_fname[11]; 
 ULONG le_fnameStatus; 
 CHAR m_sze_lname[21]; 
 ULONG le_lnameStatus; 
}; 
// EndSeekH