private static StaffInvExistsResult Check(StaffInvEntity staff, string message)
 {
     if (staff == null)
     {
         return new StaffInvExistsResult(false, message, null);
     }
     return new StaffInvExistsResult(true, null, staff);
 }
 public StaffInvExistsResult(bool isSucceed, String message, StaffInvEntity staffInv)
     : base(isSucceed, message)
 {
     this.StaffInv = staffInv;
 }