Создание уникального поля

Procedure TableNewRecord(FieldName: String;
 Var DataSet: TDataSet);
Var
  NumRec: Integer;
  bm: TBookmark;
Begin
  with DataSet do
  begin
    NumRec := Succ(RecordCount);
    if State = dsInsert then
      Post;
    bm := GetBookMark;
    DisableControls;
    while Locate(FieldName, NumRec, []) and (NumRec >  0) do
      Dec(NumRec);
    if NumRec = 0 then
    begin
      NumRec := RecordCount;
      while Locate(FieldName, NumRec, []) do
        Inc(NumRec);
    end;
    GotoBookmark(bm);
    FreeBookmark(bm);
    Edit;
    FieldByName(FieldName).AsInteger := NumRec;
    Post;
    EnableControls;
  end;
End;