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https://issues.apache.org/jira/browse/WICKET-6410?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16060967#comment-16060967
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Fabian T. commented on WICKET-6410:
-----------------------------------
Hello Martin,
Thx for your reply.
Indeed id is just null when null values are allowed in the choice. Sorry I
forgot to mention this.
Let me try to explain it with the screenshot and some code:
{code:java}
final IModel<List<ABC>> list = new AbstractReadOnlyModel<List<ABC>>() {
@Override
public List<ABC> getObject() {
List<ABC> list = some dao with to much SQL. Just used to fill
the dropdown with some initial data.
return list;
}
};
final DropDownChoice<ABC> choice = new DropDownChoice<ABC>(some wicket id,
someModel.<ABC>bind("abc"), list);
{code}
No magic here. The problem occurs after pressing submit (still no selected
element in this dropdown). Please have a look on the screenshot. As you can see
it’s just a simple submit, Wicket runs the validators and tries to bind the
selected value with the model object.
On the top, the breakpoint @ VeranstaltungenPage… line 1122: this is the
getObject method with the bigger sql.
3 lines deeper in the stacktracke, we are in the ChoiceRenderer class, line 161
(List<? extends T> _choices = choices.getObject();)
Since the user didn’t select anything in the dropdown (id = null), we’re going
the leave the ChoiceRenderer# getObject with null anyway. So the call on
IModel#getObject isn’t necessary here.
So my question, why do we need to call IModel#getObject of our dropdown?
Why not just check the id and if it’s null or empty just return null?
if (StringUtils.isBlank(id)) {
return null;
}
Since I’m not a very experience wicket dev, I’m maybe missing something
somewhere :-)
> ChoiceRenderer getObject always calls IModel#getObject when id is null
> ----------------------------------------------------------------------
>
> Key: WICKET-6410
> URL: https://issues.apache.org/jira/browse/WICKET-6410
> Project: Wicket
> Issue Type: Bug
> Components: wicket
> Affects Versions: 7.1.0
> Reporter: Fabian T.
> Priority: Trivial
> Attachments: debug_Screenshot.png
>
>
> {code:java}
> @Override
> public T getObject(String id, IModel<? extends List<? extends T>>
> choices)
> {
> List<? extends T> _choices = choices.getObject();
> for (int index = 0; index < _choices.size(); index++)
> {
> // Get next choice
> final T choice = _choices.get(index);
> if (getIdValue(choice, index).equals(id))
> {
> return choice;
> }
> }
> return null;
> }
> }
> {code}
> This Methode always calls „choices.getObject();”, even if the id is null or
> empty.
> In our project we got some bigger SQL Statements behind some getObject
> methods of different dropDownChoices. Avoiding to call getObject when the id
> is null or empty increases the performance.
> Feel free to correct me if I mess up something else with this fix.
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