CODEWITHSUNDEEP
validationdelphidatasetdelphi-2007tfield
Fabrizio
Fabrizio

Reputation: 8043

How to check the previous value of a field from the OnValidate event handler?

I need to validate the new value of a TField based on the previos value of the field itself.

e.g: the field's value can only be changed to bigger values

procedure  TForm1.FldOnValidate(AField : TField);
begin
  if(???) then
    raise Exception.Create('The new value is not bigger than the previous one');
end;

procedure TForm1.FormCreate(Sender: TObject);
var
  Dst : TClientDataSet;
  Fld : TIntegerField;
begin
  //dataset
  Dst := TClientDataSet.Create(Self);
  Dst.FieldDefs.Add('TEST', ftInteger, 0);
  Dst.CreateDataSet();
  Dst.Active := True;
  Fld := Dst.Fields[0] as TIntegerField;
  Dst.Append();
  Fld.AsInteger := 5;
  Dst.Post();
  Fld.OnValidate := FldOnValidate;


  //this should be ok (from 5 to 6)
  Dst.Edit;
  Fld.AsInteger := 6;
  Dst.Post;

  //this should not pass the validation (from 6 to 5)
  Dst.Edit;
  Fld.AsInteger := 5;
end;

I've tried to check the OldValue, NewValue, AsVariant and Value properties but I always get the new value:

procedure  TForm1.FldOnValidate(AField : TField);
begin
  ShowMessage(
    'OldValue = ' + VarToStr(AField.OldValue) + sLineBreak +
    'NewValue = ' + VarToStr(AField.NewValue) + sLineBreak +
    'AsVariant = ' + VarToStr(AField.AsVariant) + sLineBreak +
    'Value = ' + VarToStr(AField.Value)
  );
end;

Hope someone could enlighten me about that

Upvotes: 0

Views: 1899

Answers (1)

Ilyes
Ilyes

Reputation: 14928

Use Unassigned

procedure  TForm1.FldOnValidate(AField : TField);
begin
    if Sender.OldValue <> Unassigned then
      if Sender.NewValue <= Sender.OldValue then
        raise Exception.Create('The new value is not bigger than the previous one');
end;

But the right place is OnChange event

procedure TForm1.ClientDataSet1ValChange(Sender: TField);

begin
    if Sender.OldValue <> Unassigned then
      if Sender.NewValue <= Sender.OldValue then
        raise Exception.Create('The new value is not bigger than the previous one');
end;

Upvotes: 0

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