PrimaryKey and Unique Properties Example (VC++)

PrimaryKey and Unique Properties Example (VC++)

This example demonstrates the PrimaryKey and Unique properties of an Index. The code creates a new table with two columns. The PrimaryKey and Unique properties are used to make one column the primary key for which duplicate values are not allowed.

#import "c:\program files\common files\system\ado\msadox.dll" \
    no_namespace
#import "c:\program files\common files\system\ado\msado15.dll" 

#include "iostream.h"
#include "stdio.h"
#include "conio.h"

//Function Declarations
inline void TESTHR(HRESULT x) {if FAILED(x) _com_issue_error(x);};
void PrimaryKeyX(void);

//////////////////////////////////////////////////////////
//                                                      //
//    Main Function                                     //
//                                                      //
//////////////////////////////////////////////////////////
void main()
{
    if(FAILED(::CoInitialize(NULL)))
        return; 

    PrimaryKeyX();

    ::CoUninitialize();
}

//////////////////////////////////////////////////////////
//                                                      //
//        PrimaryKeyX Function                          //
//                                                      //
//////////////////////////////////////////////////////////
void PrimaryKeyX()
{
    HRESULT hr = S_OK;

    // Define ADOX object pointers.
    // Initialize pointers on define.
    // These are in the ADOX::  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:\\Program Files\\"
        "Microsoft Office\\Office\\Samples\\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);
        m_pCatalog = NULL;
    }

    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 include files...."<< endl;
    }
}