How to enable ftAutoInc in TBufDataSet?
lazarus / 16-Databases

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tatamata · 2011-08-16 07:14

It seems that ftAutoInc can't be inserted or edited in TBufDataset.
How could it be enabled in a TBufDataset descendents?

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Lacak2 · 2011-08-17 05:48

IMO it is as expected.
Auto increment (generated) fields can not be set/modified by user they
are handled by underlaying database.
BTW which error message do you receive ?
"AutoInc Fields are read-only" ?

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tatamata · 2011-08-17 06:58

Well, I want to make autoincrement generator in ZMQueryDataset, that
is TBufDataSet descendent, and is meant not to be connected to any
external database, but to work as stand-alone database.
So, the question is how to override this read-only behavior and to
enable TZMQueryDataSet to have ftAutoInc fields with internal
autoincrement generator...

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BigChimp · 2011-08-17 07:45

Quote from: Lacak2 on August 17, 2011, 07:48:11 amIMO it is as
expected.
Auto increment (generated) fields can not be set/modified by user they
are handled by underlaying database.
BTW which error message do you receive ?
"AutoInc Fields are read-only" ?
In my tests with BufDataset, autoinc didn't get any values.
If you create an autoinc field, I'd expect the values to be filled
when adding records, but that didn't happen.

Also, see
http://bugs.freepascal.org/view.php?id=19930
where ftAutoInc support is proposed to be removed from bufdataset..

Lacak, if you have a solution for getting autoinc to work in
Bufdataset (yes, read only, but at least with some auto-incrementing
values), I'm all ears (and Tatamata too, probably

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Lacak2 · 2011-08-18 05:24

Your question is very correct.
IMO there is really missing such possibility ATM.

Read-only property of TAutoIncField is coded in fields.inc, so it has
no direct relation to TBufDataSet (or any other TDataSet descendant).
TBufDataSet only holds values in their local record buffers and
allocates proper size to hold value (in this aspect ftAutoInc is equal
to ftInteger field).

So it does not matter if your dataset is local or "connected" to any
SQL database.

IMO there must be any new internal dynamic (with possibility to
override) function (for example GetNextAutoIncValue()) which will be
called just after insert if in current row will be ftAutoInc field.
But implementing this will require change deep in DB units ;-)

May be, that we can look at Delphi if there is support for such
feature.

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BigChimp · 2011-08-21 06:06

Quote from: Lacak2 on June 02, 1970, 02:00:50 amIMO there must be any
new internal dynamic (with possibility to override) function (for
example GetNextAutoIncValue()) which will be called just after insert
if in current row will be ftAutoInc field.
But implementing this will require change deep in DB units ;-)

May be, that we can look at Delphi if there is support for such
feature.
It seems that the FPC dbase units (source\packages\fcl-db\src\dbase)
have support for ftAutoInc (eg files dbf.pas, db_dbffile - procedure
procedure TDbfFile.ApplyAutoIncToBuffer(DestBuf: PChar);
Of course, it's file based but some ideas might be useful...

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tatamata · 2014-01-19 11:11

Hello, guys,

I have just successfully implemented ftAutoInc in TZMQueryDataset.
1. I searched for any "ftInteger" string in ZMBufDataset and just
added ",ftAutoInc" wherever "ftInteger" is.
2. I overrided OnNewRecord this way:
Code: [Select]procedure TZMQueryDataSet.DoOnNewRecord;
var i:integer;
begin
  inherited DoOnNewRecord;
 {New behavior}
  //Increase value of autoincrement fields
  for i:=0 to self.Fields.Count-1 do begin
     if self.Fields[i].DataType=ftAutoInc then begin
       self.Fields[i].AsInteger:=self.RecordCount+1;
     end;
  end;
end;
So, the same or similar should be done in TBufDataset, in order to
implement ftAutoInc fields.

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BigChimp · 2014-01-19 13:32

Tatamata, could you please open a bug report for that so it won't be
forgotten? Thanks a lot!

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tatamata · 2014-01-20 22:37

BigChimp, no need for that, somebody already implemented ftAutoInc in
meantime (fpc 2.7.1 has working ftAutoInc in BufDataset)

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BigChimp · 2014-01-21 06:34

Probably revision r21757.
Strange that I missed that one...

Edit: updated docs:
http://wiki.lazarus.freepascal.org/FPC_New_Features_Trunk#Bufdataset_s
upports_ftAutoInc_fields

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tatamata · 2014-01-26 18:18

Hm, it seems that there is a problem:
When TBufDataset is created and opened first time, ftAutoInc field is
working correctly,
but, if daatset is closed and then reopened again, autoincrementing
stops working, the field value is null when appending new records.

I submitted a bug: http://bugs.freepascal.org/view.php?id=25628

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BigChimp · 2014-01-26 18:55

Please see bug report for info request. Thanks.

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LacaK · 2014-01-30 09:07

Patch was commited to trunk, can you test it please?