On Tuesday 25 December 2007 9:01 am, Ed Leafe wrote:
> On Dec 24, 2007, at 6:23 PM, Adrian Klaver wrote:
> > First this based on using the full Dabo framework db-->bizobj-->ui
> > 1) Create bizobj.
> > Serves as 'template' for communicating with db and ui.
> > Also serves as local data store.
> > 2) Create ui form and controls.
> > Actually this could happen before 1).
> > Form elements can receive data from the bizobj as well as other
> > sources
> > 3) When requery() is called form afterInitAll the bizobj is
> > populated with data from
> > the DataSource i.e database table. The ui in turn uses this data to
> > fill the data controls.
> > At this point there are two versions of the data. One resident in
> > the database table,
> > the other resident in the form.
>
> Well, it's actually in the bizobj/cursor combo, but that's not an
> important distinction here.
So the data I am seeing in the form elements are an illusion?
If the data lived solely in the bizobj then form_element.update() would be
unnecessary as the element would always reflect the current state of the
bizobj.
>
> > For some time, albeit it possibly brief, they are the same.
> > 4) Changes are made to the form resident data. update() is used to
> > populate the form controls
> > when navigating in the form. At this point the form data is
> > different from the database data.
>
> As it should be, since the user just changed it.
>
> > 5) It is possible that changes have been made to the database table
> > outside of the scope of the
> > Dabo app. Again this means the db data and the form data have
> > diverged.
>
> That's true in any multi-user situation
>
> > 6) When save() is run the changes in the form are propagated back
> > to the database via the bizobj. requery() propagates changes in the
> > db to the bizobj and hence to the ui. This is where I run into a
> > problem.
> > Problem:
> > Open form with data. Make change in form field from Dabo app. Make
> > committed change in same record but different field from outside
> > app i.e. psql. From form do save(). Database has Dabo changed field
> > updated. Do requery() , db is queried but non-Dabo change is not
> > shown until an update() is done. Why?
>
> If the outside change was to a different field than the Dabo change,
> you will certainly see it if you run a requery(). Perhaps you're
> assuming that save() also runs a requery()? That wouldn't be possible
> to program, since form.save() calls either bizobj.save() or
> bizobj.saveAll(), depending on the setting of form.SaveAllRows, and
> requerying after saving just one row could possibly lose changes in
> other rows.
My sequence of operations is
bizobj.save()-->bizobj.requery(()-->self(form).update().
It is not not until I do the update() that I see the non-Dabo change.
As John pointed out it may be an artifact of using requery() from the bizobj
instead of the form. I have yet to test that theory.
>
> > Shouldn't the requery() pull in all the new data. If point 3 is
> > correct then the new form resident data should equal the db
> > resident data after the requery().
>
> Yes, that is correct, and I just verified it with MySQL. I grabbed a
> record, changed one field in Dabo, and before saving, changed a
> different column using phpMyAdmin. I then saved the change in Dabo,
> and saw only the Dabo version. I then requeried, and then saw the
> changed I had made in phpMyAdmin.
>
> The sort of thing you are describing is typical contention issues
> that are common in all multi-user situations; they are not unique to
> Dabo. Database backends each have different means available for
> dealing with contentions that vary from ignoring the issue ("last one
> wins") all the way to pessimistic transaction locking.
It is not a transaction issue as the data is committed and is viewable from
other clients immediately after the update. It is also seen by the Dabo ui
after doing a form.update().
>
> -- Ed Leafe
> -- http://leafe.com
> -- http://dabodev.com
>
>
>
>
[excessive quoting removed by server]
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