public string SaveAllocation(AllocateClassroom aClassroom)
 {
     if (aClassRoomGateway.IsSameCourseRoomDayExist(aClassroom.FromTime, aClassroom.ToTime, aClassroom.DayId, aClassroom.RoomId) != null)
     {
         return("allocation not unique");
     }
     if (aClassRoomGateway.SaveAllocation(aClassroom) > 0)
     {
         return("yes");
     }
     else
     {
         return("no");
     }
 }