I have three rules for directly referencing objects from pages
1) It's serializable
2) The valueis not going to change from the time I construct the page
to when I use the object
3) It doesn't matter if I get a copy of the object (because of deserialization).
2 & 3 can be summarized as the object being a value object
Thomas
On Mon, Jul 21, 2008 at 6:25 PM, Igor Vaynberg <[EMAIL PROTECTED]> wrote:
> the easiest thing to do is to pass the imodel<group> into the second
> page. i assume you already have a detachable group model that you are
> using to list users, so just pass it to the next page.
>
> in general keeping references to objects is safe for as long as the
> objects them selves are valid. the problem with hibernate objects is
> that although you have a reference that you can keep forever, the
> object's lifecycle is not tied to that reference. the object is tied
> to the session whose scope is usually a request, so the object itself
> is only valid during the request, which is why you have to use
> loadable detachable models.
>
> if you had an object that is not tied to any kind of lifecycle you
> could keep a reference indefinetely.
>
> once you start talking about objects that live across pages you run
> into another issue. wicket serializes each page individually. that
> means if you pass a reference to an object from page A to page B, page
> B will end up with a clone and change made to that object inside page
> B will not be visible to page A. something to keep in mind. this is
> not a problem for multiple references to an object within a page
> because serialization will properly keep track of multiple references
> to the same object.
>
> clears things up?
>
> -igor
>
> On Mon, Jul 21, 2008 at 9:10 AM, John <[EMAIL PROTECTED]> wrote:
>> hi, i am writing an application, but don't know how best to write it
>> in wicket. i can see lots of different ways to approach my problem
>> and would appreciate some direction as to which approach is the most
>> appropiate. i have read the documentation in the wiki regarding
>> models and understand the different page constructors but i am
>> confused about how long the objects are safe to hold on to and which
>> approach is best.
>>
>> here is some (pseudo)code for a page i need to write. my situation is
>> i have one page which shows the details about a "Group" (collection of
>> users), which has a link on it to create a new "User" and add it to
>> the Group. (the CreateUser page has text boxes to set name ect and
>> saves to the database on submit) my ViewGroupDetails page:
>>
>> // first decision = set the Group as a final variable before creating
>> the link so it is still there in the onClick?
>> final Group g = (Group)getModelObject();
>> new Link("adduser") {
>> public void onclick() {
>> // or get Group from the page's model only when link clicked?
>> Group g = (Group)ViewGroup.this.getModelObject();
>> // second decision = pass the whole Group into the new page constructor?
>> setResponsePage(new CreateUser(g));
>> // or make the new User object here and pass it in?
>> User u = new User();
>> u.setGroup(g);
>> setResponsePage(new CreateUser(u));
>> // or pass in just the group id number?
>> setResponsePage(new CreateUser(g.getId()));
>> }
>> }
>>
>> so the constructor of my CreateUser page will either take a Group and
>> will create the User (as above), or take a Group's id number and load
>> the Group from the database first, or take a User directly. an id
>> number could be passed in by PageParameters or directly as an integer.
>> an object could be passed bare or put inside a Model. i am not sure
>> i am making any sense! i suppose my questions are...
>>
>> - how 'safe' is it to pass the Group directly to the new page constructor?
>>
>> - is it safe to create a final reference to an object and rely on that
>> object being still there and intact by the time the link is clicked?
>>
>> - is it safe to getModelObject() to get the page's object at any time
>> in the future?
>>
>> - i understand that the following is bad: new Label(group.getId())...
>> better to use a model and load the id when needed... am i falling into
>> the same trap with the final variables in the code above?
>>
>> john
>>
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