Programmatically access external list associated column

Question

Hi I have 2 external lists 'A' and 'B'. with an associated column in A, that looks up for B. When i view/edit item in browser, it shows correct values as shown in picture below.

But when i try to access the list in code, i can access all column values, but associated column value comes null. The code look something like this :

items = listReports.GetItems();

                        System.Collections.Generic.List<ReportItem> reportItems = new List<ReportItem>();
                        foreach (SPListItem it in items)
                        {
                            if (it != null)
                            {

                                ReportItem item = new ReportItem();
            // extItem comes null
            var extItem = it["ExtCol"];
            // extItem comes null

              DateTime date;
                                if (DateTime.TryParse(it["GeneratedOn"].ToString(), out date))
                                {
                                    item.dateGenerated = date.Date;
                                }

                                DateTime time;
                                if (DateTime.TryParse(it["GeneratedOn"].ToString(), out time))
                                {
                                    item.timeGenerated = time.Date;
                                }

                                reportItems.Add(item);

                            }


                        }