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 <CAccessor<myNwCust> > 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 << "That's All Folks" << endl;

    return 1;
}
catch(...)
{
    cout << "Unknown failure" << endl;
    return -1;
}
}

The Microsoft documentation and samples are in the MSDN pages "Visual C++ Documentation \ References \ Microsoft Foundation Class Library and Templates\OLE DB Templates"


Comments

Leave a Comment
  • Your email address will not be published. All fields are required.

Top White Papers and Webcasts

  • This paper introduces IBM Java on the IBM PowerLinux 7R2 server and describes IBM's implementation of the Java platform, which includes IBM's Java Virtual Machine and development toolkit.

  • As mobile devices have pushed their way into the enterprise, they have brought cloud apps along with them. This app explosion means account passwords are multiplying, which exposes corporate data and leads to help desk calls from frustrated users. This paper will discover how IT can improve user productivity, gain visibility and control over SaaS and mobile apps, and stop password sprawl. Download this white paper to learn: How you can leverage your existing AD to manage app access. Key capabilities to …

Most Popular Programming Stories

More for Developers

Latest Developer Headlines

RSS Feeds