[SOLVED] Changing default TDataSet.delete ?
lazarus / 16-Databases

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egsuh · 2020-02-26 12:07

Hi,
Can I change the default behavior of TDataSet.Delete?

When I try to delete a record from, e.g. TBufDataSet, it asks for
"delete record?".

I'd like to add another check between this message dialog and actual
deletion, like freeing a related object so that I can avoid deleting
the record if there happen any exception at freeing the object.

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howardpc · 2020-02-26 12:15

You can assign your own event to the BeforeDelete event property of
any TDataSet descendant, and do your custom checking there.

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egsuh · 2020-02-26 15:31

Pahahahahaha...   thank you. Life would have been much easier if I
didn't think too much.

But hope that there are documentation or explanation somewhere saying
that:

    TDataset.BeforeDelete is executed when the user CLICK YES TO
"Delete Record?" prompt.

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lucamar · 2020-02-26 16:55

Quote from: egsuh on February 26, 2020, 04:31:57 pmBut hope that there
are documentation or explanation somewhere saying that:

    TDataset.BeforeDelete is executed when the user CLICK YES TO
"Delete Record?" prompt.

From the documentation:
Quote from: Reference for unit 'db' (#fcl)Description

BeforeDelete is triggered at the start of the TDataset.Delete
operation, when the dataset is still in dsBrowse state. The event
handler can be used to abort the delete operation: if an exception is
raised during the event handler, then the delete operation stops. The
event is followed by a TDataset.BeforeScroll event. If the dataset was
in insert mode when the Delete method was called, then the event will
not be called, as TDataset.Cancel is called instead.
Nothing about users clicking here or there, AFAICT

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egsuh · 2020-02-27 02:47

Quote The event handler can be used to abort the delete operation: if
an exception is raised during the event handler,
But practically how can I abort deleting?  DataSet.Cancel does not
stop deleting. How can I raise exception within BeforeDelete event
handler?

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egsuh · 2020-02-27 02:57

Well I can abort deleting in the following way.


Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i type
EDelFail = Class(exception);  procedure
TSolicitorEditor.bdsSolicitorsBeforeDelete(DataSet: TDataSet);begin 
 if not DataAccess.DeleteSolicitor (pid, sid) then      Raise
EDelFail.Create ('You cannot delete this record for some
reason');end; 
But is this the right or only way? This displays warning message
asking for OK or Abort. Users should not "abort".

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Zoran · 2020-02-27 07:51

First, do not call delete in BeforeDelete handler -- the deletion
process has started by then already.
However, you can still prevent it there.

And, instead of raising exception, use Abort (which raises "silent
exception").
Try this:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
TSolicitorEditor.bdsSolicitorsBeforeDelete(DataSet: TDataSet);begin 
if MessageDlg('Are you sure you want to delete this record?',
mtConfirmation, [mbYes, mbNo], 0) <> mrYes  then    Abort;end;

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egsuh · 2020-02-27 08:21

@Zoran

Oh yes. That's what I was looking for. Thank you very much.

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kinlion · 2022-09-28 03:14

Quote from: egsuh on February 26, 2020, 04:31:57 pmPahahahahaha... 
 thank you. Life would have been much easier if I didn't think too
much.

But hope that there are documentation or explanation somewhere saying
that:

    TDataset.BeforeDelete is executed when the user CLICK YES TO
"Delete Record?" prompt.

I think you did deleting by click the DELETE button on the navigator.
The "Delete record" message is fired by the navigator, not by the
DataSet.
You can set the "ConfirmDelete" property of the navigator to False, to
avoid the message.