does ADO has Record/Key deleted Error? - delphi

Question

i am working on Delphi 7+ SQL server.
i am converting my application from BDE to ADO.
and in some places they are handling Record/Key deleted error and the error code they are checking for is 8708.
do we have Record/Key deleted Error in ADO? and can any one please explain me in what scenario it will raise that error?

Answer 1

The following may help you exploring how to reconcile update conflicts in Sql Server tables
using TAdo* components. By way of preparation, create a table on your server with a definition like this
CREATE TABLE [dbo].[ATable](
[ID] [int] NOT NULL,
[name] [varchar](40) NOT NULL,
PRIMARY KEY CLUSTERED
(
[ID] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
and then populate it with a few rows.
Then, create a minimal Ado Delphi project with a TBGrid and TDNNavigator and the code below.
Update If you have read the original version of my answer to your q,
it talked in terms of doing batch updates on the dataset. However, since posting it, I've discovered what seems to be an anomaly in how
TAdoQuery.UpdateBatch works, so I've simplified the example code
to avoid using batched updates.
Now, compile and run the project, and open a second instance of it in a CMD window.
Change the [name] field in a row in the 2nd instance and save it, then try and make
a different change to the same row in the IDE instance. You should get an error
with words to the effect of
Record cannot be located for updating. Some values may have changed since was
last read.
How you deal with this condition is entirely up to you. You could, for example, save a local copy of the current user's version of the row's
fields, cancel the edit to the row and then fetch the new row version from the server and ask the user
whether his changes should be applied to it.
YOu should see that when the error occurs, the NativeError code is 32. Unfortunately, that is also the NativeError returned when the second
instance of the app deletes the record rather than changes it (which
makes sense in a way, because in either case, the original version
of the record no longer exists in the server table. If you want to be
able to distinguish between rows that have been changed and ones that
have been deleted, you could e.g. run a query against the table to
see if the row with the current row ID exists.
Code
type
TForm1 = class(TForm)
DataSource1: TDataSource;
DBGrid1: TDBGrid;
DBNavigator1: TDBNavigator;
ADOConnection1: TADOConnection;
ADOQuery1: TADOQuery;
Button1: TButton;
Memo1: TMemo;
procedure FormCreate(Sender: TObject);
private
procedure OnException(Sender: TObject; E: Exception);
public
end;
var
Form1: TForm1;
implementation
{$R *.dfm}
procedure TForm1.FormCreate(Sender: TObject);
begin
Application.OnException := OnException;
AdoQuery1.LockType := ltOptimistic;
AdoQuery1.CursorType := ctKeySet;
AdoQuery1.SQL.Text := 'select * from atable';
AdoQuery1.Open;
DBGrid1.Options := DBGrid1.Options + [dgEditing];
DBGrid1.Columns[0].ReadOnly := True;
end;
procedure TForm1.OnException(Sender: TObject; E: Exception);
var
AErrors : Errors;
AError : Error;
i : Integer;
S : String;
begin
Caption := 'Exception';
if E is EDatabaseError then begin
AErrors := AdoQuery1.Connection.Errors;
for i := 0 to AErrors.Count - 1 do begin
AError := AErrors.Item[i];
S := Format('Number: %d, NativeError: %d, source: %s, description: %s',
[AError.Number, AError.NativeError, AError.Source, AError.Description]);
Memo1.Lines.Add(S);
end;
end;
end;
end.