Code First

 I have 2 class

 public class Task
    {
        public int TaskId { get; set; }
        public string Discription { get; set; }
        public SpentTime SpendTimeForTask { get; set; }
        public Task() { SpendTimeForTask = new SpentTime(); }

 public class SpentTime
    {
        public int SpentTimeId { get; set; }
        public DateTime AssumedStart { get; set; }    
        public Task Task { get; set; }

    }

I want. When delete Task cascade delete SpendTimes. I write this code.

 private void DBDeleteTask(Task task) {
            using (var db = new ApplicationDbContext()) {
                var query = (from q in db.Tasks where q.Discription==task.Discription select q).Single();
                var query2 = (from q in db.SpendTimes where q.Task.Discription == query.Discription select q).Single();
                db.Tasks.Remove(query);               
                db.SaveChanges();            
               }
        }

But Delete from dataBase only Task. SpendTimes not delete