I'm pretty sure this one has been answered before but I can't figure out the correct search to get the answer.

If I write

if not table.Active then table.Open;

is the "if not table.Active then" a duplication of DBISAM's code?


Roy Lambert

Yes a Duplication, TDBISAMTable derives originally from TDataset..

By Calling Open.. In TDataset this just sets Active = TRUE which triggers
this code in TDataSet The key part being..

if Active <> Value then

So calling OPEN on a dataset thats already open does nothing...

Cheers
Clive.


procedure TDataSet.SetActive(Value: Boolean);
begin
 if (csReading in ComponentState) then
 begin
   FStreamedActive := Value;
 end
 else
   if Active <> Value then
   begin
     if Value then
     begin
       DoBeforeOpen;
       try
         OpenCursor;
       finally
         if State <> dsOpening then
           OpenCursorComplete;
       end;
     end else
     begin
       if not (csDestroying in ComponentState) then DoBeforeClose;
       SetState(dsInactive);
       CloseCursor;
       if not (csDestroying in ComponentState) then DoAfterClose;
     end;
   end;
end;






"Roy Lambert" <roy.lambert@skynet.co.uk> wrote in message
news:C8C7007E-131F-4F1C-949B-9D3C4DE878ED@news.elevatesoft.com...
> I'm pretty sure this one has been answered before but I can't figure out
> the correct search to get the answer.
>
> If I write
>
> if not table.Active then table.Open;
>
> is the "if not table.Active then" a duplication of DBISAM's code?
>
>
> Roy Lambert

IMO, you should instead do Table.Active := True which does the same
as your code below and not just for DBISAM, but for any other
database as well. Calling Open on an active dataset may cause
exception in some implementations.

Regards,
Michael

Roy Lambert wrote:
> I'm pretty sure this one has been answered before but I can't figure out the correct search to get the answer.
>
> If I write
>
> if not table.Active then table.Open;
>
> is the "if not table.Active then" a duplication of DBISAM's code?
>
>
> Roy Lambert

Michael Baytalsky <mike@contextsoft.com> wrote on Sat, 13 May 2006 20:58:27 -0400

>
>
>IMO, you should instead do Table.Active := True which does the same
>as your code below and not just for DBISAM, but for any other
>database as well. Calling Open on an active dataset may cause
>exception in some implementations.
>
>Regards,

And if I read the Help correctly, after an Open, the cursor is positioned to the first record - but I have never really known if Open on an Active dataset did the same thing , so I have always taken the bel and braces approach and done a First as well - is that necessary???????



Cheers

Jeff

--
Jeff Cook
Aspect Systems Ltd
Phone: +64-9-424 5388
Skype: jeffcooknz
www.aspect.co.nz

The answer we can found in db.pas source code, available you know where:

procedure TDataSet.Open;
begin
  Active := True;
end;

procedure TDataSet.SetActive(Value: Boolean);
begin
 ...
   if Active <> Value then
    begin
      if Value then
      begin
        DoBeforeOpen;
        try
          OpenCursor;
 ...
end;

OpenCursor -> DoInternalOpen;

procedure TDataSet.DoInternalOpen;
begin
  FDefaultFields := FieldCount = 0;
  InternalOpen;
  FInternalOpenComplete := True;
  UpdateBufferCount;
  FBOF := True; --- this line means that the cursor will be set
  (or at least expected to by Borland) to the beginning on the data set.
end;

Other then that, assigning Active or calling Open has same effect, i.e.:
1. Does nothing if the dataset is already open
2. Opens the dataset at first record if it is not

Regards,
Michael

Jeff Cook wrote:
> Michael Baytalsky <mike@contextsoft.com> wrote on Sat, 13 May 2006 20:58:27 -0400
>
>>
>> IMO, you should instead do Table.Active := True which does the same
>> as your code below and not just for DBISAM, but for any other
>> database as well. Calling Open on an active dataset may cause
>> exception in some implementations.
>>
>> Regards,
>
> And if I read the Help correctly, after an Open, the cursor is positioned to the first record - but I have never really known if Open on an Active dataset did the same thing , so I have always taken the bel and braces approach and done a First as well - is that necessary???????
>
>
>
> Cheers
>
> Jeff
>
> --
> Jeff Cook
> Aspect Systems Ltd
> Phone: +64-9-424 5388
> Skype: jeffcooknz
> www.aspect.co.nz
>  
>
>
>