Action argument is null when it shouldn't be null

[grettke_spdr]

Hi folks,

I'm running into something here where an argument to an action method is null, when I know that the value is actually not null. Here is the course of events:

A link gets displayed. The name of the link is the account number. When the link is clicked a call is made to a session scoped seam component. The argument is the account number.

<s:link id="viewDetail"
value="#{dto.accountNumber}" action="#{accountMaintenanceAction.selectAccount(dto.accountNumber)}"/>

That link gets rendered as

1024768

And when I click it the action gets run. After that the page is redirected to another page where we get the details for that account.

<page view-id="/inspectionSearch.xhtml">
 <navigation from-action="#{accountMaintenanceAction.selectAccount(dto.accountNumber)}">
 <redirect view-id="/accountMaintenance.xhtml"/>
 </navigation>
 </page>

The problem is that the argument that gets passed in to that method is null!

What am I doing wrong here?

[amitev]

Are you sure that when the action method is invoked the dto bean exists?

[grettke_spdr]

"amitev" wrote:
Are you sure that when the action method is invoked the dto bean exists?

That is a good question. The search results that carry the DTOs are inside of a session scoped component.

[fmars]

i have the same problem in a different way. The parameter passed to method is null.

i have a <s:link> in a dataTable :

<rich:dataTable value="#{genes}" var="gene" ....> ....
<s:link action="#{tableviewer.displayTargetSequences(gene)}"> ...</s:link>
.....</rich:dataTable>

tableviewer is stateless session bean for outjection the parameter and redirection.

@Stateless
@Name("tableviewer")
public class TableViewerAction implements ITableViewer{
@Out private Gene selectedGene;

public TableViewerAction() {}

public String displayTargetSequences(Gene gene) {
 selectedGene = gene;
 return "/targetSequenceViewer.xhtml";
 }
}

This bean is used only here and constructed probably right after the user clicked on it. Is this the problem?

[grettke_spdr]

"fmars" wrote:
i have the same problem in a different way. The parameter passed to method is null.
...
This bean is used only here and constructed probably right after the user clicked on it. Is this the problem?

I get the same problem if I just try passing in the dto itself, it evaluates to null.

I don't think it is a conversational problem because the dto is used to create the link tag itself (the account number), so I know exists somewhere.

Is this a lifecycle issue?

This is how the demo apps are written, but obviously I'm doing something wrong here ;)

[amitev]

I had that problem before and i solved it with long running conversation.

[amitev]

could you paste your source code?

[gayatri.ramamurthi]

1) something that skips the attention is the configuration settings which requires that the below code be added to the application config

<view-handler>org.jboss.seam.ui.facelet.SeamFaceletViewHandler</view-handler>

2) Secondly what i noticed while running a similar app is,

" #{accountMaintenanceAction.selectAccount(dto.accountNumber) } " this code generates a URL, with query string "actionMethod=example.xhtml:ccountMaintenanceAction.selectAccount(dto.accountNumber)"

whereas using #{accountMaintenanceAction.selectAccount('12345') } would generate the query string as "actionMethod=example.xhtml:ccountMaintenanceAction.selectAccount('12345')"

I think this proves that there is a problem either with the handler or any related config issue.

[fmars]

<view-handler>org.jboss.seam.ui.facelet.SeamFaceletViewHandler</view-handler>

I use Seam 2 and there is no more "SeamFaceletViewHandler".

methsearch.xhtml displays my table. The generated URL looks like this:

http://localhost:8080/methcancerdb2/methsearch.seam?
dataModelSelection=gene:genes[1]&cid=18&actionMethod=methsearch.xhtml:tableviewer.displayTargetSequences(gene)

dataModelSelection=gene:genes[1] : i've clicked link on the second row. so it is the second object in the list "genes". With gene:genes[1] is "gene" is set to genes[1]. what the rest of the url means, i don't know.

More Details:

I have this methsearch.xhtml for searching my database. there is a button "Show All", which displays all entries on the table with a <s:link> for more infos.

there is a statefull sb for this site, MethSearch.java. here is the relevant part of it:

@Stateful
@Name("methsearch")
public class MethSearch implements IMethSearch{
....
@Out(required=false)
private List<Gene> genes;

public void showAll(){
 genes = ((org.hibernate.Session)this.entityManager.getDelegate()).createCriteria(Gene.class).list();
 }
}

"genes" outjected as expected. the table displayed. only the var "gene" is not sent to method successfully. Any Idea?

[grettke_spdr]

This type of construct (passing in a dto via el) works fine in the Seam 1.2.1GA demo app: "booking".

That said, what does this article imply?

http://www.jboss.com/index.html?module=bb&op=viewtopic&t=104204

[grettke_spdr]

This code from the sample works just fine though:

<s:link id="viewHotel" value="View Hotel" action="#{hotelBooking.selectHotel(hot)}"/>

[michaelcourcy]

"grettke_spdr" wrote:
This code from the sample works just fine though:

<s:link id="viewHotel" value="View Hotel" action="#{hotelBooking.selectHotel(hot)}"/>

Yes I ran into this problem until I unserstand that a link is a link and a post is a post ;)

Wich means that using such expression

<s:link id="viewHotel" value="View Hotel" action="#{hotelBooking.selectHotel(hot)}"/>

make sens only if the #{hotelBookings} collection exist in one the available scope.

in you watch carefully the Scope of #{hotelBookings} in the seam-books example, it's a session scope.

It's really consistent, as you can engage many convesations inside a session. Session is the container of many conversations. Engaging many conversations without a session that reference them don't make sens.

When you use s:link with a one argument method you're passing a reference to an obect but you don't post this object.

But I agree on the fact that it would be more helpful if we could have an error message like : this object could not be found in any scopes (similar to struts) than having the method executed with a null argument.

I can't figure out in wich situation a developper would write

<s:link id="viewHotel" value="View Hotel" action="#{hotelBooking.selectHotel(hot)}"/>

and expecting "hot" to be null !

[grettke_spdr]

Comparing my code with the example code I found one very important difference, the collection that populates the sample is annotated with @DataModel. This is my error!

I had used a plain property of my component, that was the wrong way to do it.