Filling a List Box from a Second Recordset (MFC Data Access)

By default, a record view is associated with a single recordset object, whose fields are mapped to the record view's controls. Sometimes you might want to put a list box or combo box control in your record view and fill it with values from a second recordset object. The user can use the list box to select a new category of information to display in the record view. This topic explains how and when to do that.

Tip

Be aware that filling a combo box or list box from a data source might be slow. Take precautions against trying to fill a control from a recordset with a large number of records.

The model for this topic consists of a primary recordset that fills the controls of your form, while a secondary recordset fills a list box or combo box. Selecting a string from the list box causes your program to requery the primary recordset based on what was selected. The following procedure uses a combo box but applies equally to a list box.

To fill a combo box or list box from a second recordset

1. Create the recordset object (CRecordset.

2. Obtain a pointer to the CComboBox object for the combo box control.

3. Empty the combo box of any previous contents.

4. Move through all records in the recordset, calling CComboBox::AddString for each string from the current record you want to add to the combo box.

5. Initialize the selection in the combo box.

void CSectionForm::OnInitialUpdate()
{
    // ...

    // Fill the combo box with all of the courses
    CENROLLDoc* pDoc = GetDocument();
    if (!pDoc->m_courseSet.Open())
        return;

    // ...

    m_ctlCourseList.ResetContent();
    if (pDoc->m_courseSet.IsOpen())
    {
        while (!pDoc->m_courseSet.IsEOF() )
        {
            m_ctlCourseList.AddString(
                pDoc->m_courseSet.m_CourseID);
            pDoc->m_courseSet.MoveNext();
        }
    }
    m_ctlCourseList.SetCurSel(0);
}

This function uses a second recordset, m_courseSet, which contains a record for each course offered, and a CComboBox control, m_ctlCourseList, which is stored in the record view class.

The function gets m_courseSet from the document and opens it. Then it empties m_ctlCourseList and scrolls through m_courseSet. For each record, the function calls the combo box's AddString member function to add the course ID value from the record. Finally, the code sets the combo box's selection.

See also

Record Views (MFC Data Access)
ODBC Driver List