Re: invoking a managed bean inside a loop for another managed bean's call

[simon <si...@chello.at>]

Hi,

JSF presentation layouts (jsp pages, facelets pages, etc) are not meant
to be programming languages. They are meant only to select specific
parts of a model for presentation to the user.

So asking a backing bean for the "customers model" is fine. And
iterating over list-typed properties of the "customers model" is fine. 

But EL isn't designed for invoking backing bean methods *passing* data
from the "customers model"; that is crossing the border from "selecting
data from the model" into a generic computing language.

So you might want to rethink your approach here. If you really cannot
present a static model for the EL to pull data from, then the return
object from #{customerBean.customers} could be your own smart wrapper
class, rather than the actual model object. Then it can offer methods
that can be called via #{customer.offices} rather than trying to do a
method call officebean.offices(customer). But pause before doing this:
the fact that it isn't easy is perhaps telling you that you haven't got
the model-view-controller separation right.

Regards,

Simon

On Fri, 2008-01-04 at 18:27 -0500, M Rather wrote:
> Hello,
> 
> A similar problem as discussed in this thread.
> 
> How is the following possible in JSF: (note, read the code below as 
> pseudo code..., a ui:repeat could be a t:dataTable)
> 
> <ui:repeat var="customer" value="#{customerBean.customers}" >
>    Customer: #{customer.id} - #{customer.name} -
>     <ui:repeat var="office" value="#{officeBean.offices}">
>         Office: #{office.id}
>     </ui:repeat>
> </ui:repeat>
> 
> where officeBean.offices should take #{customer.id} as a property. So 
> for each customer displayed, display that customers' offices.
> 
> When I define officeBean as managed bean with a property for customerId, 
> I see that for all customers the same id is sent (i.e. the first one). I 
> think it is similar to the issue discussed before in this thread, that 
> when the component is built with the values are bound at that time. The 
> resolution at that time was to use 'rendered' attribute for components, 
> but how can we resolve this issue where another managed-bean's method 
> needs to be invoked in a loop and the current value in the loop needs to 
> be provided as a porperty for inner invoked method?
> 
> I also tried to define the inner manged bean with scope of 'none', 
> assuming that for each invocation it will be created and it will pickup 
> the value at that instant.. but I get the following exception:
> 
> Property [propertyName] references object in a scope with shorter 
> lifetime than the target scope none
> 
> Thanks
> MRather
> 
> 
> M Rather wrote:
> > Thanks Andrew,
> >
> > I got the desired output using the rendered attribute. Though I will 
> > test out limitRendered tag as well, I am getting some compile errors 
> > on 1.1.7 sandbox snapshot (mvn dependencies).
> >
> > For those who might see this thread, below is the code that works..
> >
> > ==================== ui:repeat with rendered=================<br/>
> >        <ui:repeat var="customer" value="${customers}" >
> >            ${customer.id} - ${customer.name} -
> >            <ui:fragment rendered="#{customer.id eq 1}">
> >              YES
> >            </ui:fragment>
> >            <ui:fragment rendered="#{customer.id ne 1}">
> >              NO
> >            </ui:fragment>
> >            <br/>
> >        </ui:repeat>
> >        ==================== ui:repeat with 
> > rendered=================<br/><br/><br/>
> >
> > and this is the generated result, as desired
> >
> > ==================== ui:repeat with rendered=================
> > 1 - cust1- YES
> > 2 - cust2 - NO
> > 3 - cust3 - NO
> > 4 - cust4 - NO
> > 5 - cust5 - NO
> > 6 - cust6 - NO
> > 7 - cust7 - NO
> > 8 - cust8 - NO
> > 9 - cust9 - NO
> > ==================== ui:repeat with rendered=================
> >
> > -MRather
> >
> 

Re: invoking a managed bean inside a loop for another managed bean's call

[M Rather <mr...@definedlogic.com>]

Thanks Simon for your revised feedback.

I still feel that making a managed-bean call in an iterator still 
satisfies separation of view from model. I think its an issue of
how JSF builds components and how it uses a value derived in an 
iterator, or I have not understood that well yet.

In any case, I managed to resolve my issue a bit differently. Here is 
how, for those who may access this thread later on.

This was the original scenario, where the inner call to 
#{officeBean.offices} would not take iterated value #{customer.id} from 
#{customerBean.customers}

<ui:repeat var="customer" value="#{customerBean.customers}" >
  Customer: #{customer.id} - #{customer.name} -
   <ui:repeat var="office" value="#{officeBean.offices}">
       Office: #{office.id}
   </ui:repeat>
</ui:repeat>

So, on my 'customerBean' I added another method called 
#{customerBean.officesByCustomers} which loads all offices for the 
customers returned by #{customerBean.customers}, and returns a map, with 
key as customer and values as a list of offices.

And, in the pseudo-code repeater I used it like this:

<ui:repeat var="customer" value="#{customerBean.customers}" >
  Customer: #{customer.id} - #{customer.name} -
   <ui:repeat var="office" 
value="#{customerBean.officesByCustomers[customer.id]}">
       Office: #{office.id}
   </ui:repeat>
</ui:repeat>

Works as expected.
The drawback is that customerBean is pretty loaded up, but I guess that 
guarantees the complete separation of view from service.

NOTE: this message is getting rejected by myfaces email server.. so I'm 
not attaching any response form previous threads in this email ..

Thanks
MRather

Re: invoking a managed bean inside a loop for another managed bean's call

[simon <si...@chello.at>]

On Sat, 2008-01-05 at 00:43 +0100, simon wrote:
> JSF presentation layouts (jsp pages, facelets pages, etc) are not meant
> to be programming languages. They are meant only to select specific
> parts of a model for presentation to the user.
> 
> But EL isn't designed for invoking backing bean methods *passing* data
> from the "customers model"; that is crossing the border from "selecting
> data from the model" into a generic computing language.

In hindsight, I may have been a little too simplistic with my earlier
reply. It *is* a good idea to avoid logic in pages, and to restrict them
to just selecting data for display. But sometimes function calls with
parameters *are* useful.

You don't mention which version of JSF you are using.

There is a wiki page here about passing parameters when using JSF1.1:
  http://wiki.apache.org/myfaces/Parameters_In_EL_Functions

I believe it is *much* easier in JSF1.2 (which uses the new "unified
EL"). However I haven't used that myself, so someone else will have to
provide the details on that.

Regards,

Simon