Totally agree! See https://issues.apache.org/jira/browse/TAPESTRY-2138
Workaround is @Persist combined with nullifying the persisted object
in cleanupRender().
Geoff
http://files.doublenegative.com.au/jumpstart/
On 23/04/2008, at 6:54 AM, Christoph Jäger wrote:
Hi,
Sorry for this long post. I spent quite some time now to try to
figure out how to use forms to edit/update objects the "right" way
(you know, simple, stable, elegant, easy to read, easy add
things, ...). I use Tapestry 5.0.11. I am almost satisfied with what
I came up with now, but some improvements need to be done. Maybe
someone on this list can help with some ideas.
As an example, lets have a PersonEdit page, with a PersonDao
injected. You can create new Person entries or edit existing ones.
To edit an existing person, there is a PageLink on a PersonSearch
page, which has the Person's primary id as context. To create a new
Person, a PageLink with 0 as context is used. To make this work, we
have onActivate() and onPassivate() methods in PersonEdit:
void onActivate(int id)
{
_id = id;
if (id == 0)
{
_person = new Person();
}
else
{
_person=personDao.get(id);
}
}
int onPassivate()
{
return _id;
}
This way we can avoid using @Persist on the Person property
(because, for instance, we want a user to be able to open two
browser windows, viewing two different Person entries side by side
and edit and save both of them. I think this would be problematic if
we use @Persist, but please correct me if I am wrong).
Now, editing an existing user works like this:
- click the "edit user XYZ" PageLink on the PersonSearch page
- in onActivate(), the personDao is used to query the Person from
the database
- an HTML form is rendered to let the user edit the values
Up to here everything looks perfect.
- the user edits the Person's data and hits the "save" button
- onActivate() is called, a fresh Person is loaded from the database
- for each field in the HTML form, validation is done (if defined),
and a property in the fresh Person instance is set if the validation
was successful
- onValidateForm() is called if existing to allow for cross-field
validation
- if all validations were successful, onSuccess() is called. Here we
call _person=personDao.save(_person). This save method returns a new
Person instance, exactly as it was written to the database (primary
id may be generated by the database, time stamps or version numbers
updated, ...). We use this new Person's id : _id=_person.getId() to
make sure we have the correct if for the next onPassivate()
- onPassivate() is called
- result sent to browser, redirect
- onActivate() loads Person again
- new form is rendered
This is good, but I think it could be improved.
1. The Person is loaded from the database twice (using
personDao.get()), and saved once. The save() method of personDao
already gives us a new, fresh instance of Person, it seems like a
waste to load it again after the redirect.
2. During validation, we check if there is already a Person with the
same userid (in onValidateForm(), or in onValidateFromUserId()) and
warn the user if this is the case. But what happens if a new Person
with this userId is added just after onValidateForm() is called, but
before onSuccess() is called, where we want to save? To make our
program solid, we have to take this into account. In case save()
does not work, we do not want to see some exception page, but the
form, as it was filled, with a hint what might have gone wrong, so
the user can try again. To make this possible, we have to move the
save() to onValidateForm(), because there we can still record form
errors (I think there is a JIRA for an improvement to this situation).
3. We want to give the user feedback of what happened. After
clicking the save button, we want to show a message like
"Successfully saved new person information" above the form (at the
same place you would see error messages like: "The first name is
mandatory"). The only thing that comes to my mind is to use @Persist
to save the message from the onSuccess() or onValidateForm() through
the redirect to the next page render. But now I have problems to
make sure this @Persist'ed message is cleared and is only presented
to the user directly after the save button was clicked.
I think to find a nice solution for these issues (you know, easy
things should be easy to do, and a form like this does not sound
very complex to me, so there should be an easy solution), a
@Persist, which persists values just through the redirect would be
very helpful. The problem is, I have no idea how this could work.
But maybe an option like this already exists (I am sure I am not the
first to have problems like this), and I just didn't find it.
Any ideas are welcome,
Thanks,
Christoph Jäger
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