TDataRecord = array of record
    FieldName: string;
    FieldValue: Variant;
  end;
 
  TMyDataSource = class(TDataSource)
  private
    LastValues: TDataRecord;
    procedure MyDataSourceBeforePost(DataSet: TDataSet);
    procedure SetDataSet(const Value: TDataSet);
    function GetDataSet: TDataSet;
  public
    constructor Create(AOwner: TComponent); override;
    destructor Destroy; override;
    function GetLastValue(FieldName: string): Variant; 
    property MyDataSet: TDataSet read GetDataSet write SetDataSet;
  end;
 
{ TMyDataSource }
 
constructor TMyDataSource.Create(AOwner: TComponent);
begin
  inherited Create(AOwner);
end;
 
destructor TMyDataSource.Destroy;
begin
  SetLength(LastValues,0);
  inherited Destroy;
end;
 
function TMyDataSource.GetDataSet: TDataSet;
begin
  Result := DataSet;
end;
 
procedure TMyDataSource.SetDataSet(const Value: TDataSet);
begin
  DataSet := Value;
  DataSet.BeforePost := MyDataSourceBeforePost;
end;
 
procedure TMyDataSource.MyDataSourceBeforePost(DataSet: TDataSet);
var
  i: integer;
begin
  SetLength(LastValues,DataSet.FieldCount);
  for i:=0 to DataSet.FieldCount-1 do
  begin
    LastValues[i].FieldName := DataSet.Fields.Fields[i].FieldName;
    LastValues[i].FieldValue := DataSet.Fields.Fields[i].OldValue;
  end;
end;
 
function TMyDataSource.GetLastValue(FieldName: string): Variant;
var
  i: integer;
begin
  Result := Null;
  for i:=0 to Length(LastValues)-1 do
    if SameText(FieldName,LastValues[i].FieldName) then
    begin
      Result := LastValues[i].FieldValue;
      break;
    end;
end;

TForm1 = class(TForm)
  private
    MyDataSource: TMyDataSource;
  end;
 
procedure TForm1.FormCreate(Sender: TObject);
begin
  ADOQuery1.Active := true;
  MyDataSource := TMyDataSource.Create(Self);
  MyDataSource.MyDataSet := ADOQuery1;
  DBGrid1.DataSource := MyDataSource;
end;
 
procedure TForm1.FormDestroy(Sender: TObject);
begin
  MyDataSource.Free;
end;
 
procedure TForm1.ADOQuery1AfterPost(DataSet: TDataSet);
var
  AValue: Variant;
begin
  AValue := MyDataSource.GetLastValue('cname');
  if not VarIsNull(AValue) then;
end;