Hi!
The code for the create button in list.xhtml.ftl looks like this:

<s:div styleClass="actionButtons" rendered="${'#'}{empty from}">
        <s:button view="/${editPageName}.xhtml"
                    id="create"
           propagation="none"
                 value="Create ${componentName}">
<#assign idName = componentName + pojo.identifierProperty.name?cap_first>
<#if c2j.isComponent(pojo.identifierProperty)>
<#foreach componentProperty in pojo.identifierProperty.value.propertyIterator>
<#assign cidName = componentName + componentProperty.name?cap_first>
            <f:param name="${cidName}"/>
</#foreach>
<#else>
            <f:param name="${idName}"/>
</#if>
        </s:button>
    </s:div>

That generates a <f:param name="${idName}"/> for the primarykey(s). Why is that done? My best guess is that it is to clear the value
of the primary key for the new object that is going to be created.

But the <f:param name="${idName}"/> actually does nothing, because in seam it is impossible to set a parameter to null. This f:params are AFAIK expected to set the method generated in EntityHome.java.ftl:

public void set${idName}(${idType} id)
    {
        setId(id);
    }

But that set is never going to be called for <f:param name="${idName}"/> because the id value is null! And there is code to prevent set${idName}(${idType} id) from being called if the value for the id is going to be null in Pages.applyConvertedValidatedValuesToMode:

private void applyConvertedValidatedValuesToModel(FacesContext facesContext)
   {
      String viewId = getViewId(facesContext);
      for ( Page page: getPageStack(viewId) )
      {
         for ( Param pageParameter: page.getParameters() )
         {
            ValueExpression valueExpression = pageParameter.getValueExpression();
            if (valueExpression!=null)
            {
               Object object = Contexts.getEventContext().get( pageParameter.getName() );
               if (object!=null) //<--- HERE IS THE PROBLEM
               {
                  valueExpression.setValue(object);
               }
            }
         }
      }
   }

Of course, it gives the impression it works, but that is just because our EntityHome is recently created and the value for the Id is initially null. But if we place our EntityHome inside a LRC, and try to use after a previous creation set the value of the Id, we will see that the Id is not reset to null by the <f:param name="${idName}"/>

A workaround I use when the id is Integer is this the -1 value:

<f:param name="${idName}" value="-1"/>

public void set${idName}(${idType} id)
    {
        if(id<0){
             setId(null);
        }else{
            setId(id);
        }
    }

But that, as it was commented in another null related discussion, a really ugly way to deal with stuff we want to be "undefined". So what can be done to fix this in Seam/seam-gen? (And of course offer a solution that can be used as a "best practice" for dealing with this even in applications that do not use seam-gen).

I propose removing the if (object!=null) from applyConvertedValidatedValuesToModel (and maybe other methods in Pages that avoid dealing with nulls in the same limited way? like perhaps convertAndValidateStringValuesInPageContext? and getStringValuesFromModel? and storeRequestStringValuesInPageContext? and possibly others...).

Now, if ignoring null values for page parameters in this way is not a bug, but a feature, then I propose removing the foreach for the create button list.xhtml.ftl, because it just creates the false impression that <f:param name="${idName}"/> actually does something.

I already created a related JIRA a while ago (https://jira.jboss.org/jira/browse/JBSEAM-3693) but guess I was not able to correctly explain this problem, I hope to have better luck this time.

Regards,
Francisco Peredo

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