BDE vs ADO Database Error handling - delphi

Question

I am working on Delphi 7 + SQLserver
in BDE all database related related erros can be handled using EDatabaseError
try
//all database related operations
Except
on EDatabaseError do
begin
showmessage(e.message)
end;
End;
but in ADO i tried different examples and i am getting different errors like EOleError/EDatabaseError/...
I Tried below 2 points to raise errors in ADO and i got different errors
1) In sql server stored procedure i am raising error on first line. when i execute that procedure using TADOStoredProc in delphi i am getting EOleError.
2) In TADOQuery i have written a wrong sql statement so when i open TADOQUery i am getting EDatabaseError.
so now i am confused how to handle ADO errors. i don't want to check for all the errors(EOleError,EDatabaseError,EAdoError...) in each and every form so i have written 2 examples,
Please suggest me which one is good. if both are wrong please give me a good example.
Example 1:
Here i am showing only one form in example so Delphi Procedure HandleErrors and function GetErrorDescription may look stupid. i don't want to write same piece of
code in all the forms. When it comes to real scenario i am gonna keep Delphi Procedure HandleErrors and function GetErrorDescription on different unit and use that unit all over the application.
type
TForm1 = class(TForm)
ADOConnection1: TADOConnection;
Button1: TButton;
procedure Button1Click(Sender: TObject);
private
{ Private declarations }
Procedure HandleErrors(e: Exception );
function GetErrorDescription : WideString;
public
{ Public declarations }
end;
var
Form1: TForm1;
implementation
{$R *.dfm}
function TForm1.GetErrorDescription : WideString;
var
LastErrorIndex : Integer;
begin
LastErrorIndex :=ADOConnection1.Errors.Count-1;
Result:=ADOConnection1.Errors.Item[LastErrorIndex].Description;
//Code :=ADOConnection1.Errors.Item[LastErrorIndex].NativeError;
end;
procedure TForm1.HandleErrors(e: Exception);
var
Code: Integer;
ErrorDescription: WideString ;
begin
if e is EOleError then
ShowMessage(GetErrorDescription)
else
if e is EDatabaseError then
ShowMessage(GetErrorDescription)
else
if e is EADOError then
ShowMessage(GetErrorDescription)
else
ShowMessage(GetErrorDescription)
end;
procedure TForm1.Button1Click(Sender: TObject);
begin
try
// any database related operations
except
on E : Exception do
begin
HandleErrors(E);
end;
end;
end;
end.
Example 2:
unit Unit1;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs,ADODB, StdCtrls, DB,COMOBJ;
type
TForm1 = class(TForm)
ADOConnection1: TADOConnection;
Button1: TButton;
procedure Button1Click(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;
var
Form1: TForm1;
implementation
{$R *.dfm}
procedure TForm1.Button1Click(Sender: TObject);
var
LastErrorIndex : Integer;
begin
try
// any database related operations
except
on E : Exception do
begin
LastErrorIndex :=ADOConnection1.Errors.Count-1;
ShowMessage(ADOConnection1.Errors.Item[LastErrorIndex].Description);
end;
end;
end;
end.
which example is better. Can you please suggest a good one

Answer 1

As I said in a comment, you shouldn't scatter AdoConnections and datasets across multiple forms/ Instead you should put them in a datamodule then Use the datamodule's unit in your forms' units. That way, you will be able to connect TDataSources and db-aware components on the form to the datamodule's datasets.
The other thing you can do is to install an application-wide exception handler to centralize your exception handling, if that's what you want to do. Delphi's Application object has an OnException event which you can assign to your own exception handler using code like that shown below.
A downside of an application-wide exception handler is that it can be difficult in the OnException handler to identify which of your objects is actually responsible for causing the exception.
type
TMainForm = class(TForm)
[...]
procedure FormCreate(Sender: TObject);
private
procedure ApplicationException(Sender: TObject; E: Exception);
public
end;
procedure TMainForm.FormCreate(Sender: TObject);
begin
Application.OnException := ApplicationException;
end;
procedure TMainForm.ApplicationException(Sender: TObject; E: Exception);
var
AErrors : Errors;
AError : Error;
i : Integer;
S : String;
begin
Caption := 'Exception';
if E is EDatabaseError then begin
AErrors := DataModule1.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;