Ejemplo de la propiedad Attributes (VC++)

Se aplica a: Access 2013, Office 2013

En este ejemplo, se muestra la propiedad Attributes de una columna. Si se establece en adColNullable, el usuario puede establecer el valor de un objeto Field de Recordset en una cadena vacía. En esta situación, el usuario puede distinguir entre un registro en el que no se conocen los datos y un registro en el que los datos no son aplicables.

 
// BeginAttributesCpp 
#import "c:\Program Files\Common Files\system\ado\msado15.dll" 
#import "c:\Program Files\Common Files\system\ado\msadox.dll" no_namespace 
 
#include "iostream.h" 
#include "stdio.h" 
#include "conio.h" 
#include "ADOXAttributesX.h" 
 
//Function declarations 
inline void TESTHR(HRESULT x) {if FAILED(x) _com_issue_error(x);}; 
void AttributesX(void); 
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; 
 
 AttributesX(); 
 
 ::CoUninitialize(); 
} 
 
////////////////////////////////////////////////////////// 
// // 
// AttributesX Function // 
// // 
////////////////////////////////////////////////////////// 
void AttributesX(void) 
{ 
 HRESULT hr = S_OK; 
 
 // Define ADOX object pointers. 
 // Initialize pointers on define. 
 // These are in the ADOX:: namespace. 
 _CatalogPtr m_pCatalog = NULL; 
 _ColumnPtr m_pColumn = NULL; 
 _TablePtr m_pTable = NULL; 
 
 // Define ADODB object pointers 
 ADODB::_ConnectionPtr m_pCnn = NULL; 
 ADODB::_RecordsetPtr m_pRstEmployees = NULL; 
 
 IADORecordBinding *picRs = NULL; // Interface Pointer Declared 
 CEmployeeRs emprs; // C++ Class Object 
 
 // Define string variables. 
 _bstr_t strcnn("Provider='Microsoft.JET.OLEDB.4.0';" 
 "Data Source= 'c:\\Program Files\\Microsoft Office\\" 
 "Office\\Samples\\Northwind.mdb';"); 
 
 try 
 { 
 // Connect the catalog. 
 TESTHR(hr = m_pCnn.CreateInstance(__uuidof (ADODB::Connection))); 
 TESTHR(hr = m_pCatalog.CreateInstance(__uuidof (Catalog))); 
 TESTHR(hr = m_pColumn.CreateInstance(__uuidof(Column))); 
 TESTHR(hr = m_pRstEmployees.CreateInstance(__uuidof(ADODB::Recordset))); 
 
 m_pCnn->Open(strcnn,"","",NULL); 
 m_pCatalog->PutActiveConnection( 
 _variant_t((IDispatch *) m_pCnn)); 
 m_pTable= m_pCatalog->Tables->GetItem("Employees"); 
 
 // Create a new Field object and append it to the Fields 
 // collection of the Employees table. 
 m_pColumn->Name = "FaxPhone"; 
 m_pColumn->Type = adVarWChar; 
 m_pColumn->DefinedSize = 24; 
 m_pColumn->Attributes = adColNullable; 
 
 m_pCatalog->Tables->GetItem("Employees")->Columns-> 
 Append(m_pColumn->Name, adVarWChar, 24); 
 //Append("FaxPhone",adVarWChar,24); 
 
 // Open the Employees table for updating as a Recordset. 
 m_pRstEmployees->Open("Employees", 
 _variant_t((IDispatch *) m_pCnn), 
 ADODB::adOpenKeyset,ADODB::adLockOptimistic, 
 ADODB::adCmdTable); 
 
 // Get user input. 
 printf("Enter fax number for : %s %s\n",(LPSTR) (_bstr_t) 
 m_pRstEmployees->Fields->GetItem("LastName")->Value, 
 (LPSTR) (_bstr_t) m_pRstEmployees->Fields-> 
 GetItem("FirstName")->Value); 
 printf("[? - unknown, X - has no fax] : \n"); 
 char strInput[10]; 
 mygets(strInput, 10); 
 char* strTemp = strtok(strInput," \t"); 
 _variant_t vNull; 
 vNull.vt = VT_BSTR; 
 vNull.bstrVal = NULL; 
 if(strTemp!=NULL) 
 { 
 if(strcmp(strTemp,"?") == 0) 
 { 
 m_pRstEmployees->Fields->GetItem("FaxPhone")-> 
 PutValue(vNull); 
 } 
 else if( (strcmp(strTemp,"X") == 0) | (strcmp(strTemp,"x") == 0) ) 
 { 
 m_pRstEmployees->Fields->GetItem("FaxPhone")-> 
 PutValue(""); 
 } 
 else 
 { 
 m_pRstEmployees->Fields->GetItem("FaxPhone")-> 
 PutValue(strTemp); 
 } 
 m_pRstEmployees->Update(); 
 
 // Open an IADORecordBinding interface pointer which 
 // we will use for binding Recordset to a class 
 TESTHR(hr = m_pRstEmployees->QueryInterface( 
 __uuidof(IADORecordBinding),(LPVOID*)&picRs)); 
 
 // Bind the Recordset to a C++ class here 
 TESTHR(hr = picRs->BindToRecordset(&emprs)); 
 
 // Print report. 
 printf("\nName - Fax number\n"); 
 printf("%s %s ",emprs.lemp_LastNameStatus == adFldOK ? 
 emprs.m_szemp_LastName : "<NULL>", 
 emprs.lemp_FirstNameStatus == adFldOK ? 
 emprs.m_szemp_FirstName : "<NULL>"); 
 
 if (emprs.lemp_FaxphoneStatus == adFldNull) 
 printf("- [Unknown]\n"); 
 else if (strcmp((LPSTR)emprs.m_szemp_Faxphone,"") == 0) 
 printf("- [Has no fax]\n"); 
 else 
 printf("- %s\n",emprs.m_szemp_Faxphone); 
 
 } 
 
 // Delete new field because this is a demonstration. 
 //m_pTable->Columns->Delete(m_pColumn->Name); 
 } 
 catch(_com_error &e) 
 { 
 // Notify the user of errors if any. 
 _bstr_t bstrSource(e.Source()); 
 _bstr_t bstrDescription(e.Description()); 
 
 printf("\n\tSource : %s \n\tdescription : %s \n ", 
 (LPCSTR)bstrSource,(LPCSTR)bstrDescription); 
 } 
 catch(...) 
 { 
 cout << "Error occured in AttributesX...."<< endl; 
 } 
 
 
 if (m_pRstEmployees) 
 if (m_pRstEmployees->State == 1) 
 m_pRstEmployees->Close(); 
 
 // Delete new field because this is a demonstration. 
 if (m_pTable != NULL) 
 m_pTable->Columns->Delete(m_pColumn->Name); 
 
 if (m_pCnn) 
 if (m_pCnn->State == 1) 
 m_pCnn->Close(); 
 
 // Release the IADORecordset Interface here 
 if(picRs) 
 picRs->Release(); 
 
} 
// EndAttributesCpp 

ADOXAttributesX.h

    // BeginAttributesH 
    #include "icrsint.h" 
     
    //This class extracts LastName, FirstName, FaxPhone from Employees table 
     
    class CEmployeeRs : public CADORecordBinding 
    { 
    BEGIN_ADO_BINDING(CEmployeeRs) 
     
     // Column LastName is the 2nd field in the table 
     ADO_VARIABLE_LENGTH_ENTRY2(2,adVarChar,m_szemp_LastName, 
     sizeof(m_szemp_LastName),lemp_LastNameStatus,TRUE) 
     
     // Column FirstName is the 17th field in the table 
     ADO_VARIABLE_LENGTH_ENTRY2(17,adVarChar,m_szemp_FirstName, 
     sizeof(m_szemp_FirstName),lemp_FirstNameStatus,TRUE) 
     
     // Column FaxPhone is the 18th field in the table 
     ADO_VARIABLE_LENGTH_ENTRY2(18,adVarChar,m_szemp_Faxphone, 
     sizeof(m_szemp_Faxphone),lemp_FaxphoneStatus,TRUE) 
     
    END_ADO_BINDING() 
     
    public: 
     CHAR m_szemp_LastName[21]; 
     ULONG lemp_LastNameStatus; 
     CHAR m_szemp_FirstName[11]; 
     ULONG lemp_FirstNameStatus; 
     CHAR m_szemp_Faxphone[25]; 
     ULONG lemp_FaxphoneStatus; 
    }; 
    // EndAttributesH