makes sense...
Just one more thing which i just noticed..not sure if it has got to with the
mounting of urls, but in certain instances i seet he jsession="[id]"
postfixed with the urls, but not for all pages, its just random..even at
times it appears for one and at a different time it doesn't. Any idea ?
igor.vaynberg wrote:
>
> On Jan 23, 2008 6:32 PM, mfs <[EMAIL PROTECTED]> wrote:
>>
>> Wouldn't the former approach have more overahead since it would first
>> load
>> the Contact (when the getmodelobject() is called) and than the deletion
>> operation..
>>
>> The later one atleast just does the deletion in one call though based on
>> its
>> primary key..
>
> well, that all depends. if you are using something like hibernate or
> something else that has a query cache then the chances of a query to
> load the object are significantly reduced. also, how often do users
> delete the object? so you are really optimizing a rare usecase...
>
> what you gain is that your UI code is not polluted with calls that
> require you to load things. you simply have an IModel to deal with.
>
> -igor
>
>
>>
>>
>>
>>
>> igor.vaynberg wrote:
>> >
>> > 1) when the page is opened the second time there will not be N
>> > selects, next time please confirm that it is indeed the case before
>> > posting to this list. it is not the case because when the page is
>> > opened the second time the items in dataview are discarded and
>> > recreated in the exact same manner as when the page was opened the
>> > first time...
>> >
>> > 2) why the detachable model is there:
>> > in order to identify an entity in the database you use its primary
>> > key. the contactdetachablemodel is like that primary key. lets assume
>> > in your dataview.populateitem() you do
>> >
>> > item.add(new link("delete", item.getmodel()) { onclick() {
>> > dao.delete(getmodelobject()); }});
>> >
>> > that link needs to be tied to the contact it needs to delete
>> > somehow...how do you do that. well you can use the model like i did
>> > above, or you can do
>> >
>> > populateitem(item item) {
>> > Contact c=item.getModelObject();
>> > item.add(new link("delete", new model(c.getid()) { onclick() {
>> > dao.deletebypk(getmodelobject()); }});
>> >
>> > but this breaks encapsulation because you need to know what contact's
>> > primary key is, it is much easier to deal with an imodel and not care.
>> > also if you need to pass this contact down to a panel, that panel can
>> > also just take an imodel and be able to retrieve that contact on
>> > subsequent requests without having to know how to do that via a
>> > primary key. makes sense?
>> >
>> > to sum up: the contactdetachablemodel is like an abstraction to a
>> > primary key and a way to retrieve the contact by its primary key.
>> >
>> > -igor
>> >
>> > On Jan 23, 2008 3:29 AM, beam <[EMAIL PROTECTED]> wrote:
>> >>
>> >> Hello everybody!
>> >> There is a page PagingPage in Wicket Examples(repeater folder)
>> >> And this page contain next code:
>> >> DataView dataView = new DataView("pageable", new
>> ContactDataProvider())
>> >>
>> >> ContactDataProvider implements method iterator:
>> >>
>> >> public Iterator iterator(int first, int count)
>> >> {
>> >> return getContactsDB().find(first, count, "firstName",
>> >> true).iterator();
>> >> }
>> >> It returns List of Contacts.
>> >>
>> >> And there is next code:
>> >> /**
>> >> * wraps retrieved contact pojo with a wicket model
>> >> *
>> >> * @see
>> >>
>> org.apache.wicket.markup.repeater.data.IDataProvider#model(java.lang.Object)
>> >> */
>> >> public IModel model(Object object)
>> >> {
>> >> return new DetachableContactModel((Contact)object);
>> >> }
>> >> So why we need to wrap every item of this List to
>> DetachableContactModel.
>> >> When page open in a first time there will be only on SELECT request
>> to
>> >> Database(iterator(int first, int count) -> SELECT * FROM Contacts
>> LIMIT
>> >> first, count)). But when page will open in a second time there will be
>> N
>> >> SELECTs (where N == count) for every Contact object in
>> >> DetachableContactModel because it calls method load().
>> >>
>> >> So I don't understand why wrap items(Contact in this example) to
>> >> DetachableContactModel? One select to retrieve all Contact on the page
>> >> better than N SELECTs, isn't it?
>> >>
>> >> P.S. Sorry for my bad english
>> >> --
>> >> View this message in context:
>> >>
>> http://www.nabble.com/Confused-with-IDataProvider-tp15039652p15039652.html
>> >> Sent from the Wicket - User mailing list archive at Nabble.com.
>> >>
>> >>
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>> >>
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>> >
>>
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>>
>> Sent from the Wicket - User mailing list archive at Nabble.com.
>>
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