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”