OLE DB Templates – A light and simple Data Access Method

I was amazed and delighted to see how simple database access has become
thanks to OLE DB. I’ve been reading the hype and so I went out and found
the Microsoft Book on OLE DB. It’s a great idea as it’s explained there
but still rather complex to code. I noticed that Visual C++ 6 has some new
templates for Data Consumers so I
started looking at the documentation. Wow! Is this simple stuff or what??

Here’s a sample, a CONSOLE application at that, using the NWind database
that comes with the DASDK. It’s only 99 lines of code including comments and
it compiles into a 60K executable.

//file: olsamp.cpp

//auth: dick warg

//date: 6/25/99

//func: minimal oledb program

#include <atldbcli.h>

#include <iostream>

using namespace std;
// define a class to hold the data from the table

class myNwCust

{

public:

    // data elements

    TCHAR m_CustomerID[6];

    TCHAR m_CompanyName[41];

    TCHAR m_ContactName[31];

    TCHAR m_Phone[25];
    // column binding  — I only want these 4 fields

    BEGIN_COLUMN_MAP(myNwCust)

        COLUMN_ENTRY(1, m_CustomerID)

        COLUMN_ENTRY(2, m_CompanyName)

        COLUMN_ENTRY(3, m_ContactName)

        COLUMN_ENTRY(4, m_Phone)

    END_COLUMN_MAP()

};
// declare the OLEDB objects

CDataSource ds;

CSession    session;

CCommand &ltCAccessor&ltmyNwCust&gt &gt cust;
int main()

{
try{

    // fire up COM

    HRESULT hr = CoInitialize(0);

    if(FAILED(hr))

    {

        cout << “Can’t start COM!? ” << endl;

        return -1;

    }
    // connect to the database

    hr = ds.Open(_T(“MSDASQL”), “OLE_DB_NWind_Jet”, “sa”, “”);

    if(FAILED(hr))

    {

        cout << “Can’t open Nwind” << endl;

        return -1;

    }
    // start the session

    hr = session.Open(ds);

    if(FAILED(hr))

    {

        cout << “Can’t open Nwind SESSION” << endl;

        ds.Close();

        return -1;

    }
    // construct the query string

    TCHAR mySQL[] = “SELECT CustomerID, CompanyName, ContactName,

    Phone FROM Customers”;
    // open the dataset

    hr = cust.Open(session, mySQL);

    if(FAILED(hr))

    {

        cout << “Can’t open Nwind TABLE” << endl;

        session.Close();

        ds.Close();

        return -1;

    }
    // read all the data

    while(cust.MoveNext() == S_OK)

    {

        cout << cust.m_CustomerID << “, ” << cust.m_CompanyName << “, “;
        cout << cust.m_ContactName << “, ” << cust.m_Phone << endl;

    }
    cust.Close();

    session.Close();

    ds.Close();
    cout &lt&lt “That’s All Folks” &lt&lt endl;
    return 1;

}

catch(…)

{

    cout &lt&lt “Unknown failure” &lt&lt endl;

    return -1;

}

}

The Microsoft documentation and samples are in the MSDN pages “Visual C++
Documentation References Microsoft Foundation Class Library and
TemplatesOLE DB Templates”