private DataModel.EntityAttr countryAttr = null;
 
public MainForm()
{
    //
    // Required for Windows Form Designer support
    //
    InitializeComponent();
    .  .  .  .  .  .  .  
    //somewhere at the form start
    countryAttr = model.EntityRoot.FindAttribute(EntAttrProp.SqlName, "Customers.Country");
}
 
//each time user updates the condition with monitored attribute,
//we refresh all lists that depends on it
private void query_ConditionsChanged(object sender, ConditionsChangeEventArgs e) {
    if (e.Condition.BaseAttr != null && e.Condition.BaseAttr == countryAttr) {
        QPanel.RefreshList("RegionList");
    }
}
 
private void QPanel_ListRequest(object sender, ListRequestEventArgs e) {
    if (e.ListName == "RegionList") {
        e.ListItems.Clear();
        string country = query.GetOneValueForAttr(countryAttr);
 
        if (country == "Canada") { 
            e.ListItems.Add("British Columbia", "BC");
            e.ListItems.Add("Quebec", "Quebec");
        }
        else if (country == "USA") {
            e.ListItems.Add("California", "CA");
            e.ListItems.Add("Colorado", "CO");
            e.ListItems.Add("Oregon", "OR");
            e.ListItems.Add("Washington", "WA");
        }
}