Hi,

i am trying this:

type
 TMPVTable = class(TDBISAMTable)
 private
   { Private-Deklarationen }
 protected
   procedure DeleteError; override;
 public
   { Public-Deklarationen }
 published
 end;

procedure Register;

implementation

procedure Register;
begin
 RegisterComponents('DBISAM', [TMPVTable]);
end;

procedure TMPVTable.DeleteError(DataSet: TDataSet;
 E: EDatabaseError; var Action: TDataAction);
begin
    ...
end;

but in line

procedure DeleteError; override;

i get a compiler error that says that this methode is not included in base class.
After a long study of the online help for hirachie and the vcl sources i cant find the
mistake.

background: i want implement some code for the events PostError, EditError, DeleteError in
a new table component

In this case i am using DBISAM V2.12 std and D5#1

thanx for reading

Thomas,

<< i get a compiler error that says that this methode is not included in
base class. After a long study of the online help for hirachie and the vcl
sources i cant find the mistake. >>

The mistake is exactly as the compiler states - there is no DeleteError
method in the base TDataSet class.  There is an *event* called
OnDeleteError, but you can't override events.

Your best bet is to override the InternalDelete method like this:

protected
     procedure InternalDelete; override;
end;

procedure TMPVTable.InternalDelete;
begin
   try
       inherited InternalDelete;
   except
       // Do error handling here
   end;
end;

You can do the same thing for InternalEdit, InternalCancel, InternalPost,
etc.  Just be sure to always call the inherited functionality.

--
Tim Young
Elevate Software
www.elevatesoft.com

Dear Tim,

"Tim Young [Elevate Software]" <timyoung@elevatesoft.com> wrote:

<<The mistake is exactly as the compiler states - there is no DeleteError
method in the base TDataSet class.  There is an *event* called
OnDeleteError, but you can't override events.>>

first of all i am not experienced with component development.
now i am a little confused. i have a tutor book for delphi, it is a besteller her in germany.
there is a chapter about component development called "Overriding standard events". there
is said you can override events methods. it is follwed by a small example.

type
 TBeepEdit = class(TEdit)
 protected
   procedure Keypress(var key:char); override;
 end;

procedure TBeepEdit.Keypress(Key);
begin
  inherited KeyPress(key);
  beep;
end;

this example works. so what is the difference in this example and my approach to overide
the OnDeleteError Event?
What have i missed?

<<Your best bet is to override the InternalDelete method like this:

protected
     procedure InternalDelete; override;
end;

procedure TMPVTable.InternalDelete;
begin
   try
       inherited InternalDelete;
   except
       // Do error handling here
   end;
end;

You can do the same thing for InternalEdit, InternalCancel, InternalPost,
etc.  Just be sure to always call the inherited functionality.>>

i will try this. but it is mostly said not to use such internal procedures. what do you
say in general about your example good or bad approach?

thanx for reading and answering.

Thomas H. Grimm

Thomas H. Grimm wrote:

> this example works. so what is the difference in this example and my approach to overide
> the OnDeleteError Event?
> What have i missed?

There happens to be a KeyPress procedure that corresponds to the
OnKeyPress property while there is no DeleteError procedure
corresponding to the OnDeleteError property. The compiler does not infer
any relationship between "property OnKeyPress" and "procedure KeyPress"
based on the name - this is just a convention adopted by the programmer.

Other common conventions that have no meaning to the compiler include
starting all fields with the letter "F" and starting the procedures and
functions that implement properties with "Get" and "Set". Just because
there is a "property This" one cannot assume that "function GetThis",
"procedure SetThis" and "FThis" necessarily exist.


> i will try this. but it is mostly said not to use such internal procedures.

"Internal" is just another naming convention adopted by whoever wrote
the original code - it has no defined meaning. If something is not meant
to be overridden then it should be registered as "private" in the base
class. Anything registered as "protected" is specifically intended to be
overridden.

Eryk

hi Eryk,

<<"Internal" is just another naming convention adopted by whoever wrote
the original code - it has no defined meaning. If something is not meant
to be overridden then it should be registered as "private" in the base
class. Anything registered as "protected" is specifically intended to be
overridden.>>

i know that these are only conventions. but if one chooses such a name he will not do this
without any reason, i think. so i am unsure if, in some circumstances, the use of such
procedure isn't problematic. perhabs may fault.

But thank you for answer. The support always was and is a big point for elevate.

Hi,


<<procedure TMPVTable.InternalDelete;
begin
   try
       inherited InternalDelete;
   except
       // Do error handling here
   end;
end;>>

so far no problem, but my error handling code looks like this

    if (E is EDBISAMEngineError) and
       (EDBISAMEngineError(E).Errors[0].ErrorCode = DBISAM_RECLOCKFAILED) then
    begin
       if (MessageDlg('fmDeleteErrorLocked', mtWarning,[mbYes,mbNo],0)=mrYes) then
          Action:=daRetry
       else
       begin
            Action:=daAbort;
       end;
    end
    else  
    begin
       MessageDlg(E.Message,mtError,[mbOk],0);
       Action:=daAbort;
    end;

it is taken from my current OnDeleteError event i use in so much cases. in your solution,
where i get the Value of E from? And how to handle the Abort or Retry statements? i only
have the dbisam std, so no sources i can investigate.

tanhx for reading and answering.

Below you can see how you can get an ExceptionObject variable E. The Event
Variable "Action" isn't usable here in this methode. So you must do
something similar to the TDataset.CheckOpertation Methode like this:


procedure TMPVTable.InternalDelete;
var
 Done: Boolean;
begin
   Done := False;
   repeat
       try
           inherited InternalDelete;
           Done := True;
       except
           // Do error handling here
           on E: EDBISAMEngineError do
           begin
               if (EDBISAMEngineError(E).Errors[0].ErrorCode =
DBISAM_RECLOCKFAILED) then
               begin
                   if (MessageDlg('fmDeleteErrorLocked',
mtWarning,[mbYes,mbNo],0)<>mrYes) then
                      SysUtils.Abort;
               end
               else
                   raise;
           end
           on E: Exception do
           begin
              MessageDlg(E.Message,mtError,[mbOk],0);
              SysUtils.Abort
           end;
       end;
   until Done;
end;


"Thomas H. Grimm" <tgrim01@web.de> schrieb im Newsbeitrag
news:5C4BF6C9-7490-422C-BD55-783D09E78BF6@news.elevatesoft.com...
> Hi,
>
>
> <<procedure TMPVTable.InternalDelete;
> begin
>    try
>        inherited InternalDelete;
>    except
>        // Do error handling here
>    end;
> end;>>
>
> so far no problem, but my error handling code looks like this
>
>     if (E is EDBISAMEngineError) and
>        (EDBISAMEngineError(E).Errors[0].ErrorCode = DBISAM_RECLOCKFAILED)
> then
>     begin
>        if (MessageDlg('fmDeleteErrorLocked',
> mtWarning,[mbYes,mbNo],0)=mrYes) then
>           Action:=daRetry
>        else
>        begin
>             Action:=daAbort;
>        end;
>     end
>     else
>     begin
>        MessageDlg(E.Message,mtError,[mbOk],0);
>        Action:=daAbort;
>     end;
>
> it is taken from my current OnDeleteError event i use in so much cases. in
> your solution,
> where i get the Value of E from? And how to handle the Abort or Retry
> statements? i only
> have the dbisam std, so no sources i can investigate.
>
> tanhx for reading and answering.
>

thank you Rolf. works like expected

Are you from switzerland?
What means "Team Elevate"?

"Rolf Frei [Team Elevate]" <rolf@eicom.ch> wrote:

Below you can see how you can get an ExceptionObject variable E. The Event
Variable "Action" isn't usable here in this methode. So you must do
something similar to the TDataset.CheckOpertation Methode like this:

Thomas,

> i know that these are only conventions. but if one chooses such a name he will not do this
> without any reason, i think. so i am unsure if, in some circumstances, the use of such
> procedure isn't problematic. perhabs may fault.

If the developer didn't want you to override a method he would make it
"private" to prevent you doing so. This is why "private" exists. Making
a method "protected" specifically invites people to override the base
functionality.

Eryk

Yes I'm from Switzerland. I'm a Volunteer for Elevatesoft which helps to
answer questions about DBIISMA 2/3 here in this forum. All this Volunteers
have the addition of "[Team Elevate]" in the name.


"Thomas H. Grimm" <tgrim01@web.de> schrieb im Newsbeitrag
news:1ECCD67B-B253-4F34-B1DC-1DEC0C5809C7@news.elevatesoft.com...
> thank you Rolf. works like expected
>
> Are you from switzerland?
> What means "Team Elevate"?
>
> "Rolf Frei [Team Elevate]" <rolf@eicom.ch> wrote:
>
> Below you can see how you can get an ExceptionObject variable E. The Event
> Variable "Action" isn't usable here in this methode. So you must do
> something similar to the TDataset.CheckOpertation Methode like this:
>