PrimaryKey- und Unique-Eigenschaften – Beispiel (VC++)

In diesem Beispiel werden die Eigenschaften PrimaryKey und Unique eines Index veranschaulicht. Der Code erstellt eine neue Tabelle mit zwei Spalten. Die Eigenschaften PrimaryKey und Unique werden verwendet, um eine Spalte zum Primärschlüssel zu machen, für den doppelte Werte nicht zulässig sind.

// BeginPrimaryKeyCpp.cpp  
// compile with: /EHsc  
#import "msado15.dll" rename("EOF", "EndOfFile")  
#import "msadox.dll" no_namespace  
  
#include "iostream"  
using namespace std;  
  
inline void TESTHR(HRESULT x) {if FAILED(x) _com_issue_error(x);};  
  
int main() {  
   if ( FAILED(::CoInitialize(NULL)) )  
      return -1;  
  
   HRESULT hr = S_OK;  
  
   // Define and initialize ADOX object pointers. These are in ADODB namespace.  
   _CatalogPtr m_pCatalog = NULL;  
   _TablePtr m_pTableNew = NULL;  
   _IndexPtr m_pIndexNew  = NULL;  
   _IndexPtr m_pIndex  = NULL;  
   _ColumnPtr m_pColumn = NULL;  
  
   // Define string variable  
   _bstr_t strcnn("Provider='Microsoft.JET.OLEDB.4.0';Data Source = 'c:\\Northwind.mdb';");  
  
   try {  
      TESTHR(hr = m_pCatalog.CreateInstance(__uuidof(Catalog)));  
      TESTHR(hr = m_pTableNew.CreateInstance(__uuidof(Table)));  
      TESTHR(hr = m_pIndexNew.CreateInstance(__uuidof(Index)));  
      TESTHR(hr = m_pIndex.CreateInstance(__uuidof(Index)));  
      TESTHR(hr = m_pColumn.CreateInstance(__uuidof(Column)));  
  
      // Connect the catalog  
      m_pCatalog->PutActiveConnection(strcnn);  
  
      // Name new table  
      m_pTableNew->Name = "NewTable";  
  
      // Append a numeric and a text field to new table.  
      m_pTableNew->Columns->Append("NumField", adInteger, 20);  
      m_pTableNew->Columns->Append("TextField", adVarWChar, 20);  
  
      // Append new Primary Key index on NumField column to new table  
      m_pIndexNew->Name = "NumIndex";  
      m_pIndexNew->Columns->Append("NumField", adInteger, 0);  
      // here "-1" is required instead of "true".  
      m_pIndexNew->PutPrimaryKey(-1);  
      m_pIndexNew->PutUnique(-1);  
      m_pTableNew->Indexes->Append(_variant_t ((IDispatch*)m_pIndexNew));  
  
      // Append an index on Textfield to new table.  Note the different technique: Specifying   
      // index and column name as parameters of the Append method  
      m_pTableNew->Indexes->Append("TextIndex", "TextField");  
  
      // Append the new table  
      m_pCatalog->Tables->Append(_variant_t ((IDispatch*)m_pTableNew));  
  
      cout << m_pTableNew->Indexes->Count << " Indexes in " << m_pTableNew->Name << " Table" << endl;  
      m_pCatalog->Tables->Refresh();  
  
      _variant_t vIndex;  
      // Enumerate Indexes collection.  
      for ( long lIndex = 0 ; lIndex < m_pTableNew->Indexes->Count ; lIndex++ ) {  
         vIndex = lIndex;  
         m_pIndex = m_pTableNew->Indexes->GetItem(vIndex);  
         cout << "Index " << m_pIndex->Name << endl;  
         cout << "   Primary key = " << (m_pIndex->GetPrimaryKey() ? "True" : "False") << endl;  
         cout << "   Unique = "  << (m_pIndex->GetUnique() ? "True" : "False") << endl;  
  
         // Enumerate Columns collection of each Index object.  
         cout << "    Columns" << endl;  
  
         for ( long lIndex = 0 ; lIndex < m_pIndex->Columns->Count ; lIndex++ ) {  
            vIndex = lIndex;  
            m_pColumn = m_pIndex->Columns->GetItem(vIndex);  
            cout << "       " << m_pColumn->Name << endl;  
         }  
      }  
  
      // Delete new table as this is a demonstration  
      m_pCatalog->Tables->Delete(m_pTableNew->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 occurred in PrimaryKeyX...." << endl;  
   }  
  
   m_pCatalog = NULL;  
   ::CoUninitialize();  
}