primefaces Datatable / sorting / wrong item

Question

I have a simple Databean like this:

@Model
Class DataBean{
    private List<Elements> elements;

    @PostConstruct
    private void loadElements(){
        //fetch data from database.
    }
}

im using Primefaces datatable to display the data, like this:

<h:form>
<p:dataTable 
      value="#{dataBean.elements}"
      var="element" >

      <p:column sortBy="#{element.id}"
           sortFunction="#{sortingHelper.sortNumericCallback}">
           <f:facet name="header">ID</f:facet>
           <p:commandLink action="#{pageController.navigateToDetailView(element)}"
                 value="#{element.id}">
           </p:commandLink>
      </p:column>
 </p:datatable>
 </h:form>

pageController.navigateToDetailView(element) simple sets the selected element on the next page's databean, so the detailView has its data prepared, and then returns the detail-Navigation-Outcome.

Now: The Problem: If i click on one of the commandLinks without any sorting, all is fine. If i sort by id and click on the details-link, the following is happening:

• Request Started
• Databean loaded (postconstruct) (sorting gone)

Now - in the second request - the page is rebuild again (in order to fire the navigateToDetailView-Action) And the datatable "knows", that i clicked on row 5. But without sorting it again, row 5 is now a different entry, since the bean gets reconstructed.

Console Output for different Points.

First I click on the page showing the Datatable. the "."'s are one comparision of my custom sort function, just to indicate the collection is sorted.

13:47:56,046 INFO  [stdout] (http--0.0.0.0-8090-1) -- Started Request --
13:47:56,047 INFO  [stdout] (http--0.0.0.0-8090-1) ---- Started RESTORE_VIEW 1 ----
13:47:56,048 INFO  [stdout] (http--0.0.0.0-8090-1) ---- Started RENDER_RESPONSE 6 ----
13:47:56,087 INFO  [stdout] (http--0.0.0.0-8090-1) PostConstruct DataBean
13:47:56,566 INFO  [stdout] (http--0.0.0.0-8090-1) -- Finished Request --

That's fine. Now im sorting by clicking the id header

13:48:15,008 INFO  [stdout] (http--0.0.0.0-8090-2) -- Started Request --
13:48:15,009 INFO  [stdout] (http--0.0.0.0-8090-2) ---- Started RESTORE_VIEW 1 ----
13:48:15,051 INFO  [stdout] (http--0.0.0.0-8090-2) ---- Started APPLY_REQUEST_VALUES 2 ----
13:48:15,052 INFO  [stdout] (http--0.0.0.0-8090-2) PostConstruct DataBean
13:48:15,124 INFO  [stdout] (http--0.0.0.0-8090-2) ..............................................................
13:48:15,124 INFO  [stdout] (http--0.0.0.0-8090-2) ---- Started PROCESS_VALIDATIONS 3 ----
13:48:15,126 INFO  [stdout] (http--0.0.0.0-8090-2) ---- Started UPDATE_MODEL_VALUES 4 ----
13:48:15,127 INFO  [stdout] (http--0.0.0.0-8090-2) ---- Started INVOKE_APPLICATION 5 ----
13:48:15,127 INFO  [stdout] (http--0.0.0.0-8090-2) ---- Started RENDER_RESPONSE 6 ----
13:48:15,387 INFO  [stdout] (http--0.0.0.0-8090-2) -- Finished Request --

That's fine, too. The Table is now sorted as it should be. Now i'm clicking on the 10th row to pick the item with the id 53;

13:48:28,295 INFO  [stdout] (http--0.0.0.0-8090-4) -- Started Request --
13:48:28,296 INFO  [stdout] (http--0.0.0.0-8090-4) ---- Started RESTORE_VIEW 1 ----
13:48:28,361 INFO  [stdout] (http--0.0.0.0-8090-4) ---- Started APPLY_REQUEST_VALUES 2 ----
13:48:28,363 INFO  [stdout] (http--0.0.0.0-8090-4) PostConstruct DataBean
13:48:28,487 INFO  [stdout] (http--0.0.0.0-8090-4) ---- Started PROCESS_VALIDATIONS 3 ----
13:48:28,501 INFO  [stdout] (http--0.0.0.0-8090-4) ---- Started UPDATE_MODEL_VALUES 4 ----
13:48:28,514 INFO  [stdout] (http--0.0.0.0-8090-4) ---- Started INVOKE_APPLICATION 5 ----
13:48:28,514 INFO  [stdout] (http--0.0.0.0-8090-4) navigateToDetail() called 
13:48:28,516 INFO  [stdout] (http--0.0.0.0-8090-4) Constructing ElementEditDataBean
13:48:28,517 INFO  [stdout] (http--0.0.0.0-8090-4) Setting ActiveElement to 42
13:48:28,518 INFO  [stdout] (http--0.0.0.0-8090-4) ---- Started RENDER_RESPONSE 6 ----
13:48:28,748 INFO  [stdout] (http--0.0.0.0-8090-4) -- Finished Request --

Note, that AFTER PostConstruct DataBean no sorting is done. (I assume since i use a form in the table, the datatable is not aware, that the sorting might have changed.)

As a result, element with id 42 is passed. (Element 42 is in the 10th position for an unsorted case)

As a result, navigateToDetailView(element) is now fired with another elementthan expected...

The Problem is ofc. that the sorted collection gets reset by the postconstruct method. I also know, that it can be solved with Conversation scope.

But I wonder if there isnt a stateless way of doing this? (I don't want to launch conversations for every sorting / page2page navigation)

Any Ideas?

Edit 1: SortingHelper is a own class, just looking like this:

 @Named
 public class SortingHelper {

/**
 * Sorts two integers correctly.
 * @param o1 integer 1
 * @param o2 integer 2
 * @return negative value if o1 is less, 0 if equal, or positive value if greater
 */
public int sortNumericCallback(Object o1, Object o2) {
    System.out.print(".");
    int i1 = Integer.parseInt((String) o1);
    int i2 = Integer.parseInt((String) o2);
    return (i1 == i2) ? 0 : (i1 > i2) ? 1 : -1;
}
 }

(Primefaces Datatable fails on sorting integers, or lets say it sorts numbers lexicographic: 11 < 5 etc.)

But even if i do not mind about the sorting and using NO custom sort function the outcome is the same.

Answer 1

As of the comments, I now modified the Databean to start a conversation after loading.

@ConversationScoped
Class DataBean{
    private List<Elements> elements;

    @Inject
    private Conversation conversation;

    @PostConstruct
    private void loadElements(){
        if (this.conversation.isTransient()) 
             this.conversation.begin();

        //fetch data from database.
    }
}

in the navigation functions of my pageController i stop that conversation again :

public String navigateToDetailView(Element element) {
    //pass element to next databean.
    conversation.end();
    //...
    return "detailView";
}

This however caused the problem, that navigating back with the browser leads to invalid conversations (they are ended).

To solve this, i created a custom filter that basically disables the caching for the browsers, so they refresh the page on history.back() and therefore having a brandnew, valid conversation id.

The Filter looks like this:

public class NoCacheFilter implements Filter {

    @Override
    public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException {
        HttpServletResponse hsr = (HttpServletResponse) res;
        hsr.setHeader("Cache-Control", "no-cache, no-store, must-revalidate"); // HTTP 1.1.
        hsr.setHeader("Pragma", "no-cache"); // HTTP 1.0.
        hsr.setDateHeader("Expires", 0); // Proxies.
        chain.doFilter(req, res);
    }

    @Override
    public void destroy() {
        // TODO Auto-generated method stub  
    }

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        // TODO Auto-generated method stub
    }
}

with this part in web.xml:

<filter>
        <filter-name>noCacheFilter</filter-name>
        <filter-class>com.example.NoCacheFilter</filter-class>
    </filter>

    <filter-mapping>
        <filter-name>noCacheFilter</filter-name>
        <url-pattern>*.xhtml</url-pattern>
    </filter-mapping>

Now i just need to figure out, how to end conversations if the user chooses no navigate away from the side, instead of calling the showDetail()-Action.