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Posted to users@wicket.apache.org by Joseph Pachod <jp...@thomas-daily.de> on 2010/07/21 17:25:14 UTC
Why is Component.setDefaultModelObject() checking for equality before
setting ?
hi
I was surprised to see, in Component.setDefaultModelObject(), the
following code:
// Check whether this will result in an actual change
if (!getModelComparator().compare(this, object))
{
modelChanging();
model.setObject(object);
modelChanged();
}
getModelComparator() being down to, by default, a simple equals between
the present model object and the object to set.
This setDefaultModelObject is called from updateModel of FormComponent.
Why is that ?
AFAIK, it brings quite some disadvantages:
- adds quite some cost (equals test can be quite expensive, and are
always more than just assigning a reference)
- if equals isn't properly implemented, can be either meaningless
(default equals being different instances are never equals even if
logically equal) or not appropriate (in entities, my equals is based on
the id, which when editing obviously causes an issue here)
- IModel implementations don't behave like that (setObject for a
PropertyModel or a Model don't check for non equality)
Yet I don't see any added value...
In the end, I see potential for misbehavior or unexpected one and no
added value.
So, why it it this way ?
thanks in advance
++
--
Joseph Pachod
IT
THOMAS DAILY GmbH
Adlerstraße 19
79098 Freiburg
Deutschland
T + 49 761 3 85 59 506
F + 49 761 3 85 59 550
E joseph.pachod@thomas-daily.de
www.thomas-daily.de
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Re: Why is Component.setDefaultModelObject() checking for equality
before setting ?
Posted by Joseph Pachod <jp...@thomas-daily.de>.
Igor Vaynberg wrote:
> the added value is that if wicket detects that the set is a noop
> because the objects are the same it doesnt need to create a new
> version of the page.
>
ok, makes more sense :)
I was quite a surprised though, I had not heard of it at all even read
all these wicket books and using wicket for quite some time. Yet making
this corner stuff more visible is probably hard.
thanks for your answer anyway
++
joseph
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Re: Why is Component.setDefaultModelObject() checking for equality
before setting ?
Posted by Igor Vaynberg <ig...@gmail.com>.
the added value is that if wicket detects that the set is a noop
because the objects are the same it doesnt need to create a new
version of the page.
-igor
On Wed, Jul 21, 2010 at 8:25 AM, Joseph Pachod <jp...@thomas-daily.de> wrote:
> hi
>
> I was surprised to see, in Component.setDefaultModelObject(), the following
> code:
> // Check whether this will result in an actual change
> if (!getModelComparator().compare(this, object))
> {
> modelChanging();
> model.setObject(object);
> modelChanged();
> }
>
> getModelComparator() being down to, by default, a simple equals between the
> present model object and the object to set.
>
> This setDefaultModelObject is called from updateModel of FormComponent.
>
> Why is that ?
>
> AFAIK, it brings quite some disadvantages:
> - adds quite some cost (equals test can be quite expensive, and are always
> more than just assigning a reference)
> - if equals isn't properly implemented, can be either meaningless (default
> equals being different instances are never equals even if logically equal)
> or not appropriate (in entities, my equals is based on the id, which when
> editing obviously causes an issue here)
> - IModel implementations don't behave like that (setObject for a
> PropertyModel or a Model don't check for non equality)
>
> Yet I don't see any added value...
>
> In the end, I see potential for misbehavior or unexpected one and no added
> value.
>
> So, why it it this way ?
>
> thanks in advance
> ++
>
> --
> Joseph Pachod
> IT
>
> THOMAS DAILY GmbH
> Adlerstraße 19
> 79098 Freiburg
> Deutschland
> T + 49 761 3 85 59 506
> F + 49 761 3 85 59 550
> E joseph.pachod@thomas-daily.de
> www.thomas-daily.de
>
> Geschäftsführer/Managing Directors:
> Wendy Thomas, Susanne Larbig
> Handelsregister Freiburg i.Br., HRB 3947
>
> Registrieren Sie sich unter https://www.thomas-daily.de/user/sign-in für die
> TD Morning News, eine kostenlose Auswahl aktueller Themen aus TD Premium,
> morgens ab 9:15 in Ihrer Mailbox.
>
> Aktuelle Presseinformationen für die TD Morning News und TD Premium nimmt
> unsere Redaktion unter redaktion@thomas-daily.de entgegen.
> Redaktionsschluss für die TD Morning News ist täglich um 8:45.
>
> Register free of charge at https://www.thomas-daily.de/user/sign-in to have
> the TD Morning News, a selection of the latest topics from TD Premium,
> delivered to your mailbox from 9:15 every morning.
>
> Our editorial department receives the latest press releases for the TD
> Morning News and TD Premium at redaktion@thomas-daily.de. The editorial
> deadline for the TD Morning News is 8.45am daily.
>
> ---------------------------------------------------------------------
> To unsubscribe, e-mail: users-unsubscribe@wicket.apache.org
> For additional commands, e-mail: users-help@wicket.apache.org
>
>
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