/// <summary> /// return the children that untreated /// </summary> /// <returns></returns> public IEnumerable <Child> UntreatedChilds(Func <Child, bool> predicate = null) { IEnumerable <Contract> conts = myIdal.GetAllContracts(); IEnumerable <Child> childs; childs = myIdal.GetAllChilds(predicate).Where(x => !conts.Any(y => y.ChildId == x.Id)); // the childs with no any contract return(childs); }