How Do I Fetch Data?

After you open the data source, session, and rowset objects, you can fetch data. Depending upon the type of accessor you are using, you may need to bind columns. To fetch data, follow these steps:

1. Open the rowset using the appropriate Open command.
   
   
2. If you are using CManualAccessor, bind the output columns if you have not already done so. To bind the columns, call GetColumnInfo, then create an accessor with the bindings, as shown here:

   // From the DBViewer Sample CDBTreeView::OnQueryEdit
   // Get the column information
   ULONG ulColumns       = 0;
   DBCOLUMNINFO* pColumnInfo  = NULL;
   LPOLESTR pStrings      = NULL;
   if (rs.GetColumnInfo(&ulColumns, &pColumnInfo, &pStrings) != S_OK)
   AfxThrowOLEDBException(rs.m_pRowset, IID_IColumnsInfo);
   struct MYBIND* pBind = new MYBIND[ulColumns];
   rs.CreateAccessor(ulColumns, &pBind[0], sizeof(MYBIND)*ulColumns);
   for (ULONG l=0; l<ulColumns; l++)
   rs.AddBindEntry(l+1, DBTYPE_STR, sizeof(TCHAR)*40, &pBind[l].szValue, NULL, &pBind[l].dwStatus);
   rs.Bind();
   

3. Write a while loop to retrieve the data. In the loop, call MoveNext to advance the cursor and test the return value against S_OK, as shown in the following example:

   while (rs.MoveNext() == S_OK)
   {
      // Add code to fetch data here
      // If you are not using an auto accessor, call rs.GetData()
   }
   

4. Within the while loop, you can fetch the data according to your accessor type.
   • If you use the CAccessor class, you should have a user record that contains data members. You can access your data using those data members, as shown here:

     while (rs.MoveNext() == S_OK)
     {
        // Use the data members directly. In this case, m_nFooID
        // is declared in a user record that derives from
        // CAccessor
        wsprintf("%d", rs.m_nFooID); 
     }
     

   • If you use the CDynamicAccessor or CDynamicParameterAccessor class, you can fetch data by using the accessing functions GetValue and GetColumn, as shown in the following code. If you want to determine the type of data you are using, use GetType.

     while (rs.MoveNext() == S_OK)
     {
        // Use the dynamic accessor functions to retrieve your
        // data
     
        ULONG ulColumns = rs.GetColumnCount();
        for (ULONG i=0; i<ulColumns; i++)
        {
          rs.GetValue(i);
        }
     }
     

   • If you use CManualAccessor, you must specify your own data members, bind them yourself, and access them directly, as shown here:

     while (rs.MoveNext() == S_OK)
     {
        // Use the data members you specified in the calls to
        // AddBindEntry.
     
        wsprintf("%s", szFoo);
     }