there is wicket-phonebook project in wicket-stuff that shows
wicket+spring+hibernate
your dropdownchoice should use a loadable detachable model, that way the
list is loaded once per request
add(new dropdownchoice("city", new loadabledetachablemodel() { load() {
return dao.listcities(); }}));
that answers question 1 and question 2 - the data will be reloaded in
onsubmit() since that is a new request, but that same data will be used for
rendering as well.
-igor
On 5/9/07, Dimitrio <[EMAIL PROTECTED]> wrote:
Hello All,
I am evaluating the possibility to use the Wicket / Spring / Hibernate
stack for my next project (Spring / Hibernate being used for the middle tier
+ OpenSessionInViewFilter).
Let me describe a simple test scenario that I am trying to implement - a
City Editor panel. The panel contains a text field with a city name and a
drop down choice with the available countries.
The domain model (mapped to the DB via Hibernate) is the following:
City
---------
Long id;
String name;
@Cascade(SAVE_UPDATE)
Country country;
Country
------------
Long id;
String isoCode;
String name;
Upon construction, the Country drop down choice for the panel is provided
with a LoadableDetachableModel that loads a list of all available countries
from a CountryDao. The form itself has a CompoundPropertyModel for the city
being edited.
The page renders just fine, the country list is correctly reloaded upon F5
- everything as expected.
However, when the user clicks Submit, the form component reloads the
country list again (so the list ends up in the new Hibernate session cache)
and when I try to save the city in onSubmit, I sometimes get a Hibernate
exception with the following message:
a different object with the same identifier value was already associated
with the session: [test.wicket.Country#6]; nested exception is
org.hibernate.NonUniqueObjectException: a different object with the same
identifier value was already associated with the session: [
test.wicket.Country#6]
This exception only occurs if the user does not change the city's country.
In that case the Country instance referenced by the city is different from
the corresponding instance in Hibernate session cache and the SAVE_UPDATE
cascading fails.
So, my first question is whether there is a way to avoid this exception?
The second thing is that I do not generally want all my reference data
being completely reloaded on every submit.
I really liked the way property editors were used in Spring to retrieve
and validate reference data for such scenarios. In Spring I would have a
CountryPropertyEditor that would retrieve the Country instance by an ISO
code or ID and assign it to the city.
So in Spring the submit would result in 2 statements like below:
select from country where id=...
update city where id=...
and avoid the duplicate instances problem altogether.
So, the second question is whether there is a way to not reload all the
reference data upon submit? How do you address such scenarios in your Wicket
applications?
Many thanks!
--Dimitrio
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