[yunqa.de] Re: How to prevent "Key Violation" errors with ClientDataSet
- From: Delphi Inspiration <delphi@xxxxxxxx>
- To: yunqa@xxxxxxxxxxxxx
- Date: Mon, 22 Feb 2010 17:50:58 +0100
At 20:36 20.02.2010, Todd Cary wrote:
>I am using version 3.6.22 and the table definition is
>
> SQL_CREATE_NOTES =
> 'CREATE TABLE Notes (' + #13#10 +
> '"ID" INTEGER PRIMARY KEY,' + #13#10 +
> '"Note" TEXT' + #13#10 +
> ')';
>
>The field type for the ID field is changed to ftAutoInc, however I do get a
>Key Violation unless I use the the procedure described below. Is there some
>setting in DISQLite3UniDirQuery or DISQLClientDataSet that I may be missing?
TClientDataSet is still a surprising mistery to me. Ironically, I was able to
reproduce your findings on a newly created project straight away (D7 and
D2010), but not on the DISQLite3_World_ClientDataSet.dpr, so I thought. But
surprisingly, I did see exactly one key violation in
DISQLite3_World_ClientDataSet.dpr (D7 only) out of an estimated 100 or more
inserts during today's testing.
For what it is worth for, I am glad to report that the problem is not
DISQLite3. It occurs somewhere deep inside TClientDataSet and, presumably,
midas.dll far before any information is passed on to DISQLite3. I am not aware
of any CDS-related options or workarounds; a web search did not turn up
anything meaningful either.
To suppress the problem, I have added the following procedure to
DISQLite3_World_ClientDataSet_Form.pas. It targets all ftAutoInc fields in a
new CDS record and fills them with a unique negative value:
procedure TfrmWorld.ClientDataSet_NewRecord(DataSet: TDataSet);
var
b: Boolean;
i: Integer;
f: TField;
begin
for i := 0 to DataSet.Fields.Count - 1 do
begin
f := DataSet.Fields[i];
if f.DataType = ftAutoInc then
begin
{ Set ftAutoInc fields to unique negative values
to avoid CDS key violations. }
b := f.ReadOnly;
f.ReadOnly := False;
Dec(FIndex); // Integer field.
f.AsInteger := FIndex;
f.ReadOnly := b;
end;
end;
end;
It should do the job for your's and others' projects as well.
Ralf
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