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Re: [GNUe] Request for trigger recipes

From: Adrian Maier
Subject: Re: [GNUe] Request for trigger recipes
Date: Wed, 1 Nov 2006 12:21:45 +0200

On 10/31/06, James Thompson <address@hidden> wrote:
On Tuesday 31 October 2006 6:21, Adrian Maier wrote:

As you can see GNUe Forms is the section (starting about 16 pages in) is where
I've been experimenting.  I think I've got most my issues
figured out and was planning to do some part/chapter re-org next followed by
a more complex master/detail example.  Instead, I'd be happy to document
triggers and include some recipes.

I'd appreciate any suggestions on topics to cover or tasks you'd like to see
put into a recipe.


As I've promised yesterday on irc , here are a few trigger recipe ideas for
the gnue-forms chapter  :

1) displaying some information  (   form.showMessage  )
2) basic manipulation of the fields'  values :   set and get . This could also
   demonstrate how to access a certain field  via   block_name.field_name .
   Possible gotchas when manipulating a field's value based on the type
   of the trigger (i don't know whether there are such situations).
3) using parameters and options
4) read a specific row from the database and do something with the values .
   This might not be specific to the gnue-forms,  but it's definitely useful
   in triggers.
5) execute a query and iterate over the rows.   Compute the average value
    based on those rows.
6) populate some fields when a new record is added , in different ways :
    with constants,   from parameters,  from another fields,  with some
    mathematical formula ,  or from a table.
7)  computing the value of a field based on other fields of the same record ,
   for example value = quantity*price ,  inside a Post-Change trigger
of the field.
8) validation that a value of a field meet certain criteria , like :
  -  the value is in a certain interval
  -  field1+field2+field3+field4 must equal 100
  There are different actions to do when the validation fails:
    (a) display a warning message (showMessage),  or
    (b) revert the field to null or some default value, or
    (c) cancel the update .... is this possible at all ?
9) look-up dialogs.  The user would press a button,   the clients are displayed,
   the user selects one of the clients and finally some fields
(client_code and
   client_name in another block) are set according to the chosen client .
   I think this is made with <dialog> and some triggers.
10) manipulate the widgets from the triggers.  For example enable/disable
   buttons, fields.
11) debugging the triggers  by "print"-ing to the console.   (are
there other simpler ways?)
12) when a field value is being modified,  is it possible to access in the same
  trigger both the OLD and the NEW value of a field?  This only makes sense
  for certain triggers .  The use case for this is :  if the NEW value
  is greater than a certain threshold,  the trigger would revert to
the OLD value.

Also, it will be perfect to have a reference of the properties and methods that
are visible to the triggers.

I hope these ideas are useful.

Many thanks,
Adrian Maier

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