Connection Close メソッド、Table Type プロパティの例 (VC++)

ActiveConnection プロパティを Nothing に設定すると、カタログが "閉じられます"。 関連付けられているコレクションは空になります。 カタログ内のスキーマ オブジェクトから作成されたオブジェクトは、すべて孤立します。 キャッシュされているそれらのオブジェクトのプロパティはすべて引き続き使用できますが、プロバイダーへの呼び出しを必要とするプロパティを読み取ろうとしても失敗します。

// BeginCloseConnectionCpp.cpp  
// compile with: /EHsc  
#import "msado15.dll" rename("EOF", "EndOfFile")  
#import "msadox.dll" no_namespace  
  
#include "iostream"  
using namespace std;  
  
// Function declarations  
inline void TESTHR(HRESULT x) {if FAILED(x) _com_issue_error(x);};  
void CloseConnectionByNothingX();  
void CloseConnectionX();  
  
int main() {  
   if ( FAILED(::CoInitialize(NULL) ) )  
      return -1;  
  
   CloseConnectionByNothingX();  
   CloseConnectionX();  
  
   ::CoUninitialize();  
}  
  
void CloseConnectionByNothingX() {  
   HRESULT hr = S_OK;  
  
   // Define and initialize ADOX object pointers, in ADODB namespace.  
   _CatalogPtr m_pCatalog = NULL;  
   _TablePtr m_pTable = NULL;  
  
   // Define ADODB object pointers  
   ADODB::_ConnectionPtr m_pCnn = NULL;  
  
   // Define other variables  
   _variant_t vIndex = (short) 0;  
  
   try {  
      TESTHR(hr = m_pCnn.CreateInstance(__uuidof(ADODB::Connection)));  
      TESTHR(hr = m_pCatalog.CreateInstance(__uuidof(Catalog)));  
  
      m_pCnn->Open("Provider='Microsoft.JET.OLEDB.4.0';Data Source= 'c:\\Northwind.mdb';", "", "", NULL);  
      m_pCatalog->PutActiveConnection(_variant_t((IDispatch *)m_pCnn));  
      m_pTable = m_pCatalog->Tables->GetItem(vIndex);  
  
      // Cache m_pTable.Type info  
      cout << m_pTable->Type << endl;  
  
      _variant_t vCnn;  
      vCnn.vt = VT_DISPATCH;  
      vCnn.pdispVal = NULL;  
      m_pCatalog->PutActiveConnection(vCnn);  
  
      // m_pTable is orphaned, will succeed if this was cached  
      cout << m_pTable->Type << endl;  
  
      cout << m_pTable->Columns->GetItem(vIndex)->DefinedSize << endl;  
      // Previous line will fail if this info has not been cached  
   }  
   catch(_com_error &e) {  
      // Notify the user of errors if any.  
      _bstr_t bstrSource(e.Source());  
      _bstr_t bstrDescription(e.Description());  
  
      printf("\nError\n\tSource :  %s \n\tdescription : %s \n", (LPCSTR)bstrSource, (LPCSTR)bstrDescription);  
   }  
   catch(...) {  
      cout << "Error occurred in CloseConnectionByNothingX...." << endl;  
   }  
}  
  
void CloseConnectionX() {  
   HRESULT hr = S_OK;  
  
   // Define ADOX object pointers, initialize pointers. These are in ADODB  namespace.  
  
   _CatalogPtr m_pCatalog = NULL;  
   _TablePtr m_pTable = NULL;  
  
   // Define ADODB object pointers  
   ADODB::_ConnectionPtr m_pCnn = NULL;  
  
   // Define other variables  
   _variant_t vIndex = (short) 0;  
   try {  
      TESTHR(hr = m_pCnn.CreateInstance(__uuidof(ADODB::Connection)));  
      m_pCnn->Open("Provider='Microsoft.JET.OLEDB.4.0';Data Source= 'c:\\Northwind.mdb';", "", "", NULL);  
  
      TESTHR(hr = m_pCatalog.CreateInstance(__uuidof(Catalog)));  
      m_pCatalog->PutActiveConnection(_variant_t((IDispatch *)m_pCnn));  
  
      m_pTable = m_pCatalog->Tables->GetItem(vIndex);  
  
      // Cache m_pTable.Type info  
      cout << m_pTable->Type << endl;  
  
      m_pCnn->Close();  
  
      // m_pTable is orphaned, will succeed if this was cached  
      cout << m_pTable->Type << endl;  
  
      cout << m_pTable->Columns->GetItem(vIndex)->DefinedSize << endl;  
      // Previous line will fail if this info has not been cached  
   }  
   catch(_com_error &e) {  
      // Notify the user of errors if any.  
      _bstr_t bstrSource(e.Source());  
      _bstr_t bstrDescription(e.Description());  
  
      printf("\nError\n\tSource :  %s \n\tdescription : %s \n", (LPCSTR)bstrSource, (LPCSTR)bstrDescription);  
   }  
   catch(...) {  
      cout << "Error occurred in CloseConnectionX...." << endl;  
   }  
}  

参照

ActiveConnection プロパティ (ADOX)