Let me give you a short example to put the above said into a meanigfull
context:
Lets says I have a database table, which stores customers all of which I would
like to list row by row in a JSF table, which is contained inside a single JSP
page. Each row also contains action links which represent actions that can be
performed on a customer, like edit, delelete, display and "add another address".
For the JSP page I only need a reference to a DataModel.
The reference to the instance of the DataModel should be obtained from a
"context variable", which references an "instance" of a class, which implements
DataModel and is kept in one of the 5 seam contexts.
If I name the jsp page "displayCustomers.jsp" and call it via a GET request,
then I run into the fact, that the context variable is not accessible, because
no seam component get's referenced in a MVC pull fashion from the page.
That's what I meant by saying ".jsp pages, which do not contain any value or
method binding".
Because no calls to a seam component have been made from the jsp page, the no
context variable for the DataModel has not been set.
I could use a Page Action, to achievie this so that it calls some method on a
seam component that sets the context variable and loads the clients from the
database before the .jsp file gets rendered like this:
@DataModel @Out
@Factory("loadClientsFromDatabase")
List clients;
But I find that cumbersome, because I have so many pages which list entities
the same fashion.
And using "pull-MVC" defeats the purpose of the @DataModel, because the idea of
using it is not having to use "pull-MVC". I mean if I use something like:
<h:dataTable value="#{seamcomponent.loadClientsViaPullMVC}" var="c"
rendered="#{seamcomponent.loadClientsViaPullMVC.rowCount>0}">
Then I don't need a @DataModel inside "seamcomponent" anymore. I also noticed,
that it is not possible to use @DataModelSelection in a seam component, which
does not also contain the @DataModel annotation.
That I find also strange, because I can think of many use cases in which you
would want another seam component to retrieve the selected Customer to perform
some actions on him.
For example, if I had a "action link" add address, then in the AddAdressAction
I would want to place a @DataModelSelection to get the selected Customer from.
If I do this currently, then I won't be able to easily retrieve the customer. I
have to put "AddAddressAction.add()" method into the Seam Bean, which has the
DataModel, where it does not belong and increases component dependancy.
I hope in this light my last post makes more sense?!
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