Delphi - TDataSet determine if it was modified when is in insert/edit state

Question

how can I find out if an data-aware component field has been modified when the dataset is already in Insert state? I want to know if a field was 'really' modified. (I don't care if the user has input something in a field and after that erase everything, this mean that a modification occured).

DataSet.Modified, DataSet.UpdateStatus or ChangeCount are not solving my problem.

LE: let me explain more in depth this. so, initial dataset looks like

-------------------------------------
|PK  | Field1| Field2| Field3|Field4|
-------------------------------------
| 1  |  a    | b     | c     | d    |  
-------------------------------------

after insert

-------------------------------------
|PK  | Field1| Field2| Field3|Field4|
-------------------------------------
| 2  |       |       |       |      |  
-------------------------------------
| 1  |  a    | b     | c     | d    |  
-------------------------------------

when the dataset is really modified

-------------------------------------
|PK  | Field1| Field2| Field3|Field4|
-------------------------------------
| 2  | avalue|       |       |      |  
-------------------------------------
| 1  |  a    | b     | c     | d    |  
-------------------------------------

Answer 1

You could hack the DataSet to change it's Modified property on AfterInsert/AfterEdit (and set initial/default values) and later test for DataSet.Modified (e.g. on before post).
To determine which specific fields were modified, I hold a copy of the initial record e.g.:

type
  TDataRecord = array of record
    FieldName: string;
    Value: Variant;
  end;

type
  TForm1 = class(TForm)
    ... 
  private
    FInitRecord, FPostRecord: TDataRecord;
  end;

function GetDataRecord(DataSet: TDataSet): TDataRecord;
var
  I: Integer;
begin
  Result := nil;
  if Assigned(DataSet) then begin
    SetLength(Result, DataSet.FieldCount);
    for I := 0 to DataSet.FieldCount - 1 do begin
      Result[I].FieldName := DataSet.Fields[I].FieldName;
      Result[I].Value := DataSet.Fields[I].Value;
    end;
  end;
end;

type
  TDataSetAccess = class(TDataSet);

procedure TForm1.ADODataSet1AfterInsert(DataSet: TDataSet);
begin
  // set initial values 
  ADODataSet1.FieldByName('PK').Value := GetMyPKValue;
  ADODataSet1.FieldByName('DateCreated').AsDateTime := Now(); 
  // un-modify
  TDataSetAccess(ADODataSet1).SetModified(False);
  // save initial record
  FInitRecord := GetDataRecord(ADODataSet1);
end;    

procedure TForm1.ADODataSet1BeforePost(DataSet: TDataSet);
var
  I: Integer;
begin
  if ADODataSet1.Modified then
  begin
    FPostRecord := GetDataRecord(ADODataSet1);
    Memo1.Lines.Clear;
    for I := 0 to Length(FPostRecord) - 1 do begin
      if FPostRecord[I].Value <> FInitRecord[I].Value then
        Memo1.Lines.Add(Format('Field %s was modified', [FPostRecord[I].FieldName]));
    end;
  end;
end;

Well, It's the abstract idea anyway. You could sub-class your TDataSet like I do, and implement this feature directly inside your TDataSet component.

Answer 2

When the state is dsInsert use:

VarCompareValue(Field.NewValue, Unassigned) = vrNotEqual;

dsEdit use:

OldValue <> Value;

Do not use this in dsInsert state as in numeric Fields 0 is equal Unassigned:

Field.NewValue <> Unassigned

Answer 3

Until now I found a solution, which seems to work. Solution consist in: - link a datasource to the tdataset descendant - a global boolean variable is set to false on the dataset OnAfterScroll event, and true on the datasources's OnDataChange event.

From the tests I performed on the application until now, it seems that this work-around is working. I need now to investigate all the events which occur and need special treatment for not altering the state of the global variable in the process.

Any other ideas are welcomed