10:52 a.m.
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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